Until Microsoft created Visual C++ 4, database programmers had some difficulty justifying Visual C++ as a mainstream database development platform. Visual C++'s sole support for database developers was ODBC. Visual C++ didn't support the more powerful (and useful) Microsoft Jet database engine. In fact, Visual C++ programmers often were told by Visual Basic programmers that they had a better database development platform. Today, with Visual C++ 4, Visual C++ programmers are no longer at such a disadvantage. They now have access to the Microsoft Jet database engine and DAO (Database Access Objects).
WARNING
The DAO database classes are meant for single-threaded operation only. Don't try to utilize these classes in more than one thread at one time.
With Visual C++ 4, the DAO database classes are considered distinct from the MFC ODBC database classes. All of the DAO database class names have a prefix of CDao. Usually the DAO classes are more powerful than the ODBC classes. DAO classes use the Microsoft Jet database engine to access data. In turn, the Microsoft Jet database engine uses ODBC drivers to access data that isn't supported directly. The DAO classes also support the Data Definition Language (DDL) operations—for example, operations for creating databases and adding tables and fields via the classes—all without having to call DAO directly.
This chapter documents the new MFC classes that support the DAO interface. These classes (seven main new classes and several more supporting classes and structures) are very similar to their ODBC database counterparts, such as CDatabase and CRecordset.
Generally, the majority of Visual C++ database applications will be written using AppWizard and will be expanded by the programmer to become complete, working database applications. It's possible to write a database application from scratch using the DAO database classes—and a few programmers do. However, neither Microsoft nor the authors recommend doing this. With this in mind, your database application will have a few of the classes included by AppWizard (these classes are described next). During the development cycle, you will probably add other classes.
The MFC classes for DAO are like all other MFC classes. They serve as wrappers, encapsulating DAO's basic functionality. For example:
This process continues through the other DAO MFC classes.
Not all of the DAO functionality is encapsulated in the DAO MFC classes. You'll find that the major DAO objects are supported, but some objects, such as fields, indexes, parameters, and relations, aren't directly supported by the DAO MFC objects.
NOTE
There are three technical papers (called Technical Notes) specific to DAO:
TN053 Writing Custom DFX Routines for DAO Database Classes TN054 Calling DAO Directly While Using MFC DAO Classes TN055 Migrating MFC ODBC Database Class Applications to MFC DAO Classes
NOTE
Technical Note 54 (in the Visual C++ Books Online, see Visual C++ Books, MFC 4.0, MFC Technical Notes) has an example of using nonencapsulated DAO functionality in an MFC application.
Table 13.1 shows a mapping of DAO objects to MFC classes. The Comments and Related ODBC Classes column lists the corresponding ODBC class when applicable.
| MFC Class | DAO Object | Comments and Related ODBC Classes |
| CDaoWorkspace | Workspace | Manages the transaction space. Provides the Microsoft Jet database engine access. |
| CDaoDatabase | Database | Represents a connection to a specific database. Similar to CDatabase. |
| CDaoTableDef | Tabledef | Determines and manipulates the structure of a given table. |
| CDaoQueryDef | Querydef | Saves queries in a database. |
| CDaoRecordset | Recordset | Manages the result set, a set of records based on a table or selected by a query. Similar to CRecordset. |
| CDaoException | Error | MFC responds to all DAO errors by throwing exceptions of this type. |
| CDaoFieldExchange | None | Manages the exchange of data between a record in the database and the field data members of a recordset. Similar to CFieldExchange. |
The following sections document the DAO MFC classes by showing significant member functions and giving examples of usage.
As I mentioned earlier, some of the DAO MFC classes have ODBC analogues. This makes it easier to convert ODBC applications to use the DAO MFC classes. Generally, if you're unsure whether you should use DAO or ODBC, you should choose DAO to base your application on if the underlying database structure is either Access or one of the database structures that DAO supports directly (such as FoxPro).
NOTE
All DAO functions require the DAO header. Use the statement #include <afxdao.h>. When you use AppWizard to create an application, the #include is added automatically.
NOTE
See the DAO MFC documentation for more information about each of the DAO MFC classes. Simply search for the class name in the Books Online in Visual C++.
The CDaoWorkspace object is the highest object in the DAO hierarchy. It represents the DAO Workspace object. The DAO workspace defines the session for the user. It contains open databases and support for simultaneous transactions.
The CDaoWorkspace object manages named database sessions (from initial logon to logoff) for a single user. This database may be password protected. Generally, an application will use a single workspace. With AppWizard applications, it's unnecessary to create an explicit Workspace object. If your application needs multiple sessions, you can create additional Workspace objects. For each Workspace object, there may be more than one open database object at any given time. Under MFC's implementation, the workspace is basically a manager of transactions.
The CDaoWorkspace class provides the following functionality:
The DAO MFC classes don't implement the security control Users and Groups collections. When security is a concern, you will need to provide the necessary interface using direct calls to the underlying DAO interface.
NOTE
For information on accessing the underlying DAO interface, go to Books Online and search for the topic Technical Note 54.
The CDaoWorkspace call may be used to do the following things:
In order to use CDaoWorkspace to create a new workspace that doesn't exist in the Workspaces collection, use the CDaoWorkspace.Create() member function. With CDaoWorkspace, workspace objects won't persist between Microsoft Jet database engine sessions. If your application links MFC statically (that is, you link the MFC code using a static library rather than a DLL), when the application ends, the Microsoft Jet database engine will still be initialized. However, if the application uses MFC using the MFC DLL, the Microsoft Jet database engine will be uninitialized when the MFC DLL is unloaded.
Use the Open() member function to open an existing workspace. Use the Close() member function to close a workspace session. When Close() is called, all databases that haven't already been closed will be closed. Also, all uncommitted transactions will be rolled back (discarded).
DAO is used to manage transactions at the workspace level. As such, any transactions to workspaces with more than one open database will be applied to all open databases. For example, if there are two databases with uncommitted updates, and there is a call to CommitTrans(), all of the updates are committed, regardless of which database the changes are being applied to. When it's necessary to limit your transactions to one of a number of open databases, you must create a separate workspace object for the database to which you wish to limit your transactions.
Your application will use the DAO default workspace implicitly when the following events occur:
The CDaoWorkspace class provides a host of other database operations, such as repairing corrupted databases or compacting databases. Table 13.2 lists the members of the CDaoWorkspace class.
| Member | Description |
| Data Members | |
| m_pDAOWorkspace | A pointer to the basic underlying DAO workspace object. |
| Construction | |
| CDaoWorkspace() | A constructor for the CDaoWorkspace object. After creating the CDaoWorkspace object, you must call either Create() or Open(). |
| Attributes | |
| GetIsolateODBCTrans() | Returns a value used to indicate whether multiple transactions that involve the same ODBC data source are isolated. |
| GetName() | Returns the user-defined name for the Workspace object. |
| GetUserName() | Returns the user name (workspace owner) specified when the workspace was created. |
| IsOpen() | Returns a nonzero value if the workspace is open. |
| SetIsolateODBCTrans() | Specifies whether multiple transactions that involve the same ODBC data source will be isolated. |
| Operations | |
| Append() | Appends a newly created workspace to the database engine's Workspaces collection. |
| BeginTrans() | Begins a new transaction. The new transaction will apply to all databases open in the workspace. |
| Close() | Closes the workspace and all of the objects it contains. If there are any pending transactions, they are rolled back (discarded). |
| CommitTrans() | Completes the current transaction and saves the specified changes. |
| CompactDatabase() | Compacts (or duplicate) the database. |
| Create() | Creates a new DAO Workspace object. |
| GetDatabaseCount() | Returns a value that indicates the number of DAO Database objects in the workspace's Databases collection. |
| GetDatabaseInfo() | Returns information about a specified DAO database defined in the workspace's Databases collection. |
| GetWorkspaceCount() | Returns the number of DAO Workspace objects in the database engine's Workspaces collection. |
| GetWorkspaceInfo() | Returns information about a specified DAO workspace defined in the database engine's Workspaces collection. |
| Open() | Explicitly opens a workspace object associated with DAO's default workspace. |
| RepairDatabase() | Attempts to repair a damaged database. |
| Rollback() | Ends the current transaction. Any changes won't be saved. |
| Idle() | Allows the database engine to perform background tasks. |
| Database Engine Properties | |
| GetVersion() | Returns a string that contains the version of the database engine associated with the workspace. |
| GetIniPath() | Returns the location of the Microsoft Jet database engine's initialization settings in the Windows registry. |
| GetLoginTimeout() | Returns the number of seconds before an error occurs when the user attempts to log in to an ODBC database. |
| SetDefaultPassword() | Sets the password that the database engine uses when a workspace object is created without a specific password. |
| SetDefaultUser() | Sets the user name that the database engine uses when a workspace object is created without a specific user name. |
| SetIniPath() | Sets the location of the Microsoft Jet database engine's initialization settings in the Windows registry. |
The CDaoDatabase object is used to represent the connection to a database (from the CDaoWorkspace object) through which you can operate on the database's data.
NOTE
For more information on which database formats are supported, refer to the CDaoWorkspace::GetName() member function in the Visual C++ Books Online.
More than one CDaoDatabase object may be active at a given time in a given CDaoWorkspace object. The workspace maintains a collection of open database objects called the Databases collection. For more information, see the section "CDaoWorkspace."
You can create CDaoDatabase database objects implicitly when you create Recordset objects. You also can create a CDaoDatabase object explicitly. If you want to use an existing database explicitly with CDaoDatabase, you can do one of the following:
NOTE
It's possible to create a new Microsoft Access (.MDB) database. First, construct a CDaoDatabase object, and then call the CDaoDatabase object's Create() member function. It's not proper to call Open() after Create() in this situation.
When using CDaoDatabase, you may open an existing database by creating the CDaoDatabase object and then calling the Open() member function.
Each of these techniques will append a CDaoDatabase object to your CDaoWorkspace object and then open a connection to the database's data. You then will create CDaoRecordset, CDaoTableDef, or CDaoQueryDef objects to utilize the database. When CDaoRecordset, CDaoTableDef, or CDaoQueryDef objects are created, you pass to the constructors for these objects a pointer to your CDaoDatabase object. When the application has finished working with the connection, a call to the Close() member function closes the connection. You then must close any recordsets that you haven't already closed and destroy the CDaoDatabase object.
NOTE
If you already know ODBC, things might be starting to look familiar since ODBC and DAO share a common model. The following paragraphs discuss transaction processing—which, except for class names, works like ODBC's transaction processing.
DAO provides transaction processing at the workspace level. See the CDaoWorkspace::BeginTrans, CDaoWorkspace::CommitTrans, and CDaoWorkspace::Rollback functions in the Visual C++ Books Online. For additional information about transactions, search for the article "DAO Workspace: Managing Transactions" in the Programming with MFC title in Books Online.
As I mentioned earlier, DAO can interface with ODBC data sources. Microsoft recommends that you attach your ODBC data sources to a Microsoft Access (.MDB) database as external tables. For further information about this technique, see the article "DAO External: Working with External Data Sources" in the Programming with MFC title in Books Online.
With DAO, each database will maintain its own collections of Tabledef, Querydef, Recordset, and Relation objects. The DAO CDaoDatabase class will supply the necessary member functions to allow your application to manipulate these objects. These objects are stored in DAO itself, not in the DAO MFC class objects. There are also MFC classes for Tabledef, Querydef, and Recordset objects. There is no MFC class for Relation objects at this time.
Table 13.3 lists the members of the CDaoDatabase class.
| Member | Description |
| Data Members | |
| m_pWorkspace | A pointer to the CDaoWorkspace object that contains the database. |
| m_pDAODatabase | A pointer to the underlying DAO CDaoDatabase object. |
| Construction | |
| CDaoDatabase | Constructs the CDaoDatabase object. After construction, you call Open() to connect the object to a database. |
| Attributes | |
| CanTransact() | Returns a nonzero value if the database supports transactions. |
| CanUpdate() | Returns a nonzero value if the CDaoDatabase object may be updated. If the Database object is read-only, this function returns a zero value. |
| GetConnect() | Returns the connect string that was used to connect the CDaoDatabase object to a database. |
| GetName() | Returns the name of the database currently in use. |
| GetQueryTimeout() | Returns the time-out period (in seconds) after which database query operations will time out. |
| GetRecordsAffected() | Returns a count of the number of records that were affected by the last update, edit, add operation, or call to Execute(). |
| GetVersion() | Returns the version of the database engine associated with the database. |
| IsOpen() | Returns a nonzero value if the CDaoDatabase object is currently connected to a database. |
| SetQueryTimeout() | Sets in seconds the time-out period after which database query operations will fail. SetQueryTimeout() affects all subsequent open, add new, update, and delete operations. |
| Operations | |
| Close() | Closes the database connection. |
| Create() | Creates the underlying DAO database object and then initializes the CDaoDatabase object. |
| CreateRelation() | Defines a new relation among the tables in the database. |
| DeleteQueryDef() | Deletes a Querydef object saved in the database's QueryDefs collection. |
| DeleteRelation() | Deletes existing relations between tables in the database. |
| DeleteTableDef() | Deletes a table's definition in a database. When that table's definition is deleted, all the table's data is also deleted. |
| Execute() | Causes the action query to be executed. This query shouldn't return any results. If the executed query returns any results, an exception of type CDaoException is returned. |
| GetQueryDefCount() | Returns the number of queries defined for the database. |
| GetQueryDefInfo() | Returns information about a specified query defined in the database. |
| GetRelationCount() | Returns the number of relations defined between tables in the database. |
| GetRelationInfo() | Returns information about a specified relation defined between tables in the database. |
| GetTableDefCount() | Returns the number of tables defined in the database. |
| GetTableDefInfo() | Returns information about a specified table in the database. |
| Open() | Opens a database and establishes a connection to it. |
The DAO CDaoTableDef object is used to represent the stored definition of a base table or a table that is attached. Each DAO database object has a collection called TableDefs that contains all the saved DAO Tabledef objects.
You can manipulate a table definition with CDaoTableDef. Here are some things you can do using CDaoTableDef:
To work with an existing table or create a new table, you will use Tabledef objects. First, construct a CDaoTableDef object. Next, give CDaoTableDef a pointer to a CDaoDatabase object to which the table belongs. Then you have to do one of the following things. What you do depends on what you want to do in your application:
It's easy to create tables using Microsoft Access. Open the database in Access, create your tables, and save the database. Using Access for this type manipulation is easier than trying to have your Visual C++ application perform these tasks. Of course, if your application must perform this functionality, and you're reasonably sure that all users of your application won't have Access available, you'll have to perform this task using your Visual C++ application instead of Access.
You specify a name for the Tabledef with a dbOpenTable value in the nOpenType parameter when opening a CDaoRecordset.
When using a Tabledef object to create a CDaoRecordset object, you might follow the steps just mentioned. After creating the object, construct your Recordset object using a pointer to your Tabledef object when you call CDaoRecordset::Open(). When you pass a Tabledef, it must be open.
As with other objects, when you're finished using the Tabledef object, call its Close() member function. After closing the Tabledef object, destroy it.
Table 13.4 lists the members of the CDaoTableDef class.
| Member | Description |
| Data Members | |
| m_pDatabase | Contains a pointer to the source database for this table. |
| m_pDAOTableDef | Contains a pointer to the DAO interface underlying this Tabledef object. |
| Construction | |
| Append() | Adds a new table to the database. |
| CDaoTableDef() | Constructs a CDaoTableDef object. |
| Close() | Closes an open Tabledef. |
| Create() | Creates a table that can be added to the database using the Append() function. |
| Open() | Opens an existing Tabledef stored in the database's TableDefs collection. |
| Attributes | |
| CanUpdate() | Determines whether a table can be updated. If CanUpdate() returns a nonzero value, the table can be updated. |
| GetAttributes() | Determines the characteristics of a CDaoTableDef object. |
| GetConnect() | Gets information about the source of a table. |
| GetDateCreated() | Gets the creation date and time for the base table underlying a CDaoTableDef object. |
| GetDateLastUpdated() | Gets the date and time of the last change to the base table. |
| GetFieldCount() | Determines the number of fields in the table. |
| GetFieldInfo() | Obtains information about fields in the table. |
| GetIndexCount() | Determines the number of indexes to the table. |
| GetIndexInfo() | Obtains information about indexes to the table. |
| GetName() | Obtains the user-defined table name. |
| GetRecordCount() | Determines the number of records in the table. |
| GetSourceTableName() | Obtains the name of the attached table in the source database. |
| GetValidationRule() | Obtains the validation rule that is used to validate the data in a field as it is changed or added to a table. |
| GetValidationText() | Obtains a value that specifies the text of the message that your application displays if the value of a Field object doesn't satisfy the specified validation rule. |
| IsOpen() | Determines whether a table is open or not. Returns a zero value if the table isn't open. |
| SetAttributes() | Sets the value that is used to change one or more characteristics of a CDaoTableDef object. |
| SetConnect() | Sets values that are used in the connection to the table. |
| SetName() | Sets the name of the table. |
| SetSourceTableName() | Sets the source table's name. |
| SetValidationRule() | Sets a validation rule. The validation rule is used every time data in a field is changed (or added) to a table. |
| SetValidationText() | Sets the message that is to be displayed whenever data doesn't meet the specifications described by the validation rule. |
| Operations | |
| CreateField() | Creates a field for a table. |
| CreateIndex() | Creates an index for a table. |
| DeleteField() | Deletes a field from a table. |
| DeleteIndex() | Deletes an index from a table. |
| RefreshLink() | Updates the connection information for an attached table. |
A Querydef is a query definition that is usually (but doesn't have to be) stored or saved in a database. Access databases often have query definitions stored in them. Querydefs consist of SQL statements that describe a query, the query's properties (such as the date it was created), and the time-out value. Since Querydefs don't need to be stored in a database, they can also be temporary objects. It isn't unusual for a Visual C++ front-end application to create a temporary Querydef object.
NOTE
Querydefs are always more efficient if they're stored in the database. Any Querydef that is to be executed frequently should always be saved in the database.
The CDaoDatabase object will maintain a collection, the QueryDefs collection, containing the object's saved Querydefs.
You can use CDaoQueryDef to work with saved queries and to create a new saved or temporary query. You would use CDaoQueryDef in the following way. First, you would create and construct your CDaoQueryDef object. This object would be supplied with the pointer to your CDaoDatabase object to which the query will belong. Next, you must do one of the following:
After you've finished using the Querydef object, call the Close() member function to close it. As soon as the Querydef is closed, destroy the CDaoQueryDef object.
You can easily create Querydef objects using Microsoft Access. Open the database, design your query, and save it. Your Visual C++ database application can then use the query.
A Querydef object is used for either of the following:
All types of queries can be used as Querydef objects. For example, queries can take the form of select, action, crosstab, delete, update, append, make-table, data definition, SQL pass-through, union, or bulk queries. The SQL statement that makes up the query determines the type of query.
See the Execute() and GetType() member functions in the Visual C++ Books Online for more information about queries. A query that would return a set of rows (as a recordset) is usually in the form of SELECT rows FROM table types of SQL statements.
When you use a Querydef to create a CDaoRecordset object, you create (or open) a Querydef. Then a CDaoRecordset object would be created and passed a pointer to your Querydef object. This pointer would be passed in the call to CDaoRecordset::Open(). The Querydef you pass must itself be open. If the Querydef isn't open, it can't be used to create a recordset.
You would use a Querydef object to gain access to the native SQL dialect for an external (non-Access) database. If you needed to create a Transact SQL query (Transact is the version of SQL used by Microsoft SQL Server), you would create the query and store it as a Querydef object.
Table 13.5 lists the members of the CDaoQueryDef class.
| Member | Description |
| Data Members | |
| m_pDatabase | Contains a pointer to the CDaoDatabase object to which the Querydef is associated, whether the Querydef is saved or not. |
| m_pDAOQueryDef | Contains a pointer to the OLE interface for the underlying DAO Querydef object. |
| Construction | |
| CDaoQueryDef() | Constructs the CDaoQueryDef object. After the CDaoQueryDef object is created, you must call either Open() or Create(). |
| Create() | Creates the underlying DAO Querydef object. The query can be either temporary or saved using a call to the Append() member function. |
| Append() | Appends the Querydef to the database's QueryDefs collection. This will make the Querydef a saved (not temporary) object. |
| Open() | Opens an existing Querydef stored in the database's QueryDefs collection. |
| Close() | Closes the Querydef object. |
| Attributes | |
| CanUpdate() | Returns a zero result if the database can't be updated. |
| GetConnect() | Obtains the connect string associated with the Querydef. |
| GetDateCreated() | Obtains the query's creation date. |
| GetDateLastUpdated() | Obtains the query's last update date. |
| GetName() | Returns the name of the Querydef. |
| GetODBCTimeout() | Obtains the ODBC timeout value. |
| GetRecordsAffected() | Determines the count of how many records have been affected by an action query. |
| GetReturnsRecords() | Returns zero if the query doesn't return any records. |
| GetSQL() | Returns the SQL string that specifies the query defined by the Querydef. |
| GetType() | Determines what the query type is. The query type could be delete, update, append, make-table, and so on. |
| IsOpen() | Returns zero if the Querydef isn't open or can't be executed. |
| SetConnect() | Sets the connect string for an SQL pass-through query on an ODBC data source. |
| SetName() | Sets the name of the saved query. This new name replaces the name that was in use when the Querydef was created. |
| SetODBCTimeout() | Sets the timeout period to be used by ODBC. |
| SetReturnsRecords() | Specifies that the Querydef will return records. |
| SetSQL() | Sets the SQL string that specifies the query defined by the Querydef. |
| Operations | |
| Execute() | Executes the query defined by the Querydef object. |
| GetFieldCount() | Determines the number of fields that this Querydef has defined. |
| GetFieldInfo() | Determines information about a field that is specified in the query. |
| GetParameterCount() | Determines the number of parameters defined for the query. |
| GetParameterInfo() | Obtains information about the specified parameter in the query. |
| GetParamValue() | Gets the value of a specified parameter to the query. |
| SetParamValue() | Sets the value of a specified parameter to the query. |
The DAO class CDaoRecordset is used to represent a set of records that have been selected from a datasource. CDaoRecordset corresponds directly to the CRecordset object that is used with ODBC.
The main difference between the DAO recordset and the ODBC recordset is that CDaoRecordset class objects access data through DAO, which is based on OLE, while the CRecordset classes access the database using ODBC.
A CDaoRecordset object is known as a recordset. A CDaoRecordset object can take one of three forms: a table-type recordset, a dynaset-type recordset, or a snapshot-type recordset:
The records contained in the recordset are fixed at the time the recordset is opened. Both the table-type recordset and dynaset-type recordset will reflect any changes made to data after the recordset was opened (by either the current process or perhaps by other users). In contrast, the snapshot recordset is static and isn't updated. Many applications use CDaoRecordset directly (usually using classes created using AppWizard). However, you can derive a class from CDaoRecordset if you wish. When you have a recordset object, you can do the following:
To use the CDaoRecordset object, first you must open a database and construct your CDaoRecordset object. A pointer to your CDaoDatabase object must be passed to the constructor. Alternatively, it's possible to create a CDaoRecordset object and have MFC create a temporary CDaoDatabase object.
After you've created the CDaoRecordset, you must call the Open() member function. It takes a parameter that specifies whether the object is to be a table-type recordset, a dynaset-type recordset, or a snapshot-type recordset. Calling Open() selects data from the database and retrieves the first record.
After you've created your recordset object, you then can use the object's member functions and data members to scroll through the records and perform operations on them.
The CDaoRecordset class uses DAO record field exchange (DFX) to support the reading and updating of record fields through type-safe C++ members of your CDaoRecordset or CDaoRecordset-derived class. See the CDaoFieldExchange object in the Visual C++ Books Online for more information.
Table 13.6 lists the members of the CDaoRecordset class.
| Member | Description |
| Data Members | |
| m_bCheckCacheForDirtyFields | Contains a flag indicating whether fields are automatically marked as changed or not. |
| m_pDAORecordset | A pointer to the DAO interface underlying the recordset object. |
| m_nParams | Has the number of parameter data members that will be found in the CDaoRecordset class. |
| m_pDatabase | Contains a pointer to the source database that the result set was created from. The pointer is of type CDaoDatabase. |
| m_strFilter | Contains a string that is used to construct an SQL WHERE statement. |
| m_strSort | Contains a string used to construct an SQL ORDER BY statement. |
| Construction | |
| CDaoRecordset() | Constructs a CDaoRecordset object. |
| Close() | Closes a CDaoRecordset object. |
| Open() | Creates a new table, dynaset, or snapshot recordset. |
| Attributes | |
| CanAppend() | Determines if new records may be added to a recordset using the AddNew() member function. This function returns zero if new records can't be added to the recordset. |
| CanBookmark() | If the recordset support bookmarks, this function returns a nonzero value. |
| CanRestart() | If Requery() can be called to run the query again, this function returns a nonzero value. |
| CanScroll() | If you can scroll through the records, this function returns a nonzero value. |
| CanTransact() | If the datasource supports transactions, this function returns a nonzero value. |
| CanUpdate() | If the datasource supports updates, this member function returns a nonzero value. |
| GetCurrentIndex() | Used to obtain a CString that will contain the name of the index that was most recently used. |
| GetDateCreated() | Obtains the date and time that the base table underlying the CDaoRecordset object was created. |
| GetDateLastUpdated() | Obtains the date and time of the most recent change made to the design of a base table underlying a CDaoRecordset object. |
| GetEditMode() | Returns a value that will indicate the editing state for the current record. |
| GetLastModifiedBookmark() | Determines the most recently added or updated record. |
| GetName() | Returns the name of the recordset as a CString. |
| GetParamValue() | Retrieves the current value of the specified parameter stored in the underlying DAOParameter object. |
| GetRecordCount() | Obtains the number of records accessed in a Recordset object. |
| GetSQL() | Gets the SQL string used to select records for the recordset. |
| GetType() | Determines the recordset's type: table, dynaset, or snapshot. |
| GetValidationRule() | Retrieves the validation rule for a field. |
| GetValidationText() | Retrieves the message text that is to be displayed when a validation rule isn't satisfied. |
| IsBOF() | Returns a nonzero value if the recordset has been positioned before the first record. There is no current record. |
| IsDeleted() | Returns a nonzero value if the recordset is currently positioned on a deleted record. |
| IsEOF() | Returns a nonzero value if the recordset has been positioned after the last record. There is no current record. |
| IsFieldDirty() | Returns a nonzero value if the specified field in the current record has been changed. |
| IsFieldNull() | Returns a nonzero value if the specified field in the current record is null. Remember that null is different from NULL. |
| IsFieldNullable() | Returns a nonzero value if the specified field in the current record can be set to null. |
| IsOpen() | Returns a nonzero value if Open() has been called previously. |
| SetCurrentIndex() | Sets an index on a table-type recordset. |
| SetParamValue() | Sets the current value of the specified parameter stored in the underlying DAOParameter object. |
| SetParamValueNull() | Sets the current value of the specified parameter to null. |
| Recordset Update Operations | |
| AddNew() | Sets up for adding new records. After the new records are prepared, a call to Update() will complete the record-adding process. |
| CancelUpdate() | Called when it's necessary to abort or cancel pending updates due to an Edit() or an AddNew() operation. |
| Delete() | Deletes the current record from the recordset. After the current record is deleted, it's necessary to explicitly scroll to another record. |
| Edit() | Prepares for edits in the current record. After completing the edits, you must call Update() to update the record or call CancelUpdate() to cancel the changes. |
| Update() | Completes an AddNew() or Edit() operation by saving the new or edited data on the data source. |
| Recordset Navigation Operations | |
| Find() | Finds the first, next, previous, or last location of a specified string in a recordset. The recordset must be a dynaset type that satisfies the specified criteria and makes that record the current record. |
| FindFirst() | Finds the first location of a specified string in a recordset. The recordset must be a dynaset type that satisfies the specified criteria and makes that record the current record. |
| FindLast() | Finds the last location of a specified string in a recordset. The recordset must be a dynaset type that satisfies the specified criteria and makes that record the current record. |
| FindNext() | Finds the next location of a specified string in a recordset. The recordset must be a dynaset type that satisfies the specified criteria and makes that record the current record. |
| FindPrev() | Finds the previous location of a specified string in a recordset. The recordset must be a dynaset type that satisfies the specified criteria and makes that record the current record. |
| GetAbsolutePosition() | Returns the record number of a recordset object's current record. |
| GetBookmark() | Returns a value that represents the bookmark on a record. |
| GetPercentPosition() | Returns the position of the current record as a percentage of the total number of records. |
| Move() | Repositions the recordset to a specified number of records relative to the current record. The move may be either forward or backward. |
| MoveFirst() | Positions the current record to the first record in the recordset. |
| MoveLast() | Positions the current record to the last record in the recordset. |
| MoveNext() | Positions the current record to the next record in the recordset. |
| MovePrev() | Positions the current record to the previous record in the recordset. |
| Seek() | Finds a record and makes that record the current record. |
| SetAbsolutePosition() | Sets the record number of a recordset object's current record. |
| SetBookmark() | Positions the recordset to a record that contains the specified bookmark. |
| SetPercentPosition() | Sets the position of the current record to a location that corresponds to a given percentage based on the total number of records in a recordset. |
| Other Recordset Operations | |
| FillCache() | Fills all (or a part) of the local cache for a recordset object. |
| GetCacheSize() | Returns the number of records in a dynaset-type recordset to be locally cached. |
| GetCacheStart() | Returns the bookmark value of the first record in the recordset to be cached. |
| GetFieldCount() | Returns the number of fields in the recordset. |
| GetFieldInfo() | Returns specific kinds of information about the fields in the recordset. |
| GetFieldValue() | Returns a field's value. |
| GetIndexCount() | Retrieves the number of indexes in a table. |
| GetIndexInfo() | Returns information on an index. |
| GetLockingMode() | Determines the type of locking that is in effect. |
| Requery() | Reruns the recordset's query to refresh the selected records. |
| SetCacheSize() | Sets the cache size. |
| SetCacheStart() | Sets the bookmark of the first record in the recordset to be cached. |
| SetFieldDirty() | Marks the specified field in the current record as changed. |
| SetFieldNull() | Specifies that the field is null. |
| SetFieldValue() | Specifies the value of a field in a recordset. |
| SetFieldValueNull() | Sets the value of a field to null. |
| SetLockingMode() | Sets the type of locking to put into effect during editing. |
| Overridables | |
| DoFieldExchange() | Performs the exchange of data between the field data members and the record set's current record. |
The CDaoException object is used when handling exceptions when using the DAO MFC classes. The CDaoException class includes several public data members that may be used to analyze the error and assist you in determining the cause of the exception. CDaoException objects are constructed and thrown by member functions of the DAO database classes.
You can access exception objects within the scope of a CATCH expression. Your application also can throw a CDaoException object by using an AfxThrowDaoException() global function.
NOTE
The Microsoft documentation mentions the file DAOERR.H. This file is actually called DBDAOERR.H.
Table 13.7 lists error codes from DBDAOERR.H.
| Error Code | Description |
| E_DAO_InternalError | A reserved error, because there is no message for this error. |
| E_DAO_InvalidParameter | Invalid argument. |
| E_DAO_CantBegin | Couldn't start the session. |
| E_DAO_TransTooDeep | Couldn't start the transaction. Too many transactions were already nested. |
| E_DAO_DatabaseNotFound | Couldn't find the database. |
| E_DAO_DatabaseInvalidName | Name specified isn't a valid database name. |
| E_DAO_DatabaseLocked | Database is exclusively locked. |
| E_DAO_DatabaseOpenError | Can't open the library database. |
| E_DAO_TableLocked | Table is exclusively locked. |
| E_DAO_TableInUse | Couldn't lock table because it's currently in use. |
| E_DAO_TableDuplicate | Table already exists. |
| E_DAO_ObjectNotFound | Couldn't find object. |
| E_DAO_ObjectDuplicate | Object already exists. |
| E_DAO_CannotRename | Couldn't rename installable ISAM file. |
| E_DAO_TooManyOpenTables | Can't open any more tables. |
| E_DAO_IndexNotFound | The index specified isn't an index in this table. |
| E_DAO_ColumnDoesNotFit | Field won't fit in record. |
| E_DAO_ColumnTooBig | The size of a field is too long. |
| E_DAO_ColumnNotFound | Couldn't find the field. |
| E_DAO_NoCurrentIndex | Operation invalid without a current index. |
| E_DAO_RecordNoCopy | Update or CancelUpdate without AddNew() or Edit(). |
| E_DAO_NoCurrentRecord | No current record. |
| E_DAO_KeyDuplicate | Duplicate value in index, primary key, or relationship. Changes were unsuccessful. |
| E_DAO_AlreadyPrepared | AddNew() or Edit() already used. |
| E_DAO_FileNotFound | Couldn't find file. |
| E_DAO_TooManyOpenFiles | Can't open any more files. |
| E_DAO_DiskFull | Not enough space on the disk. |
| E_DAO_PermissionDenied | Can't update because the database or object is read-only. |
| E_DAO_CannotOpenSystemDb | Can't start the application. The system database is missing or opened exclusively by another user. |
| E_DAO_InvalidLogon | Not a valid account name or password. |
| E_DAO_InvalidAccountName | Not a valid account name. |
| E_DAO_InvalidPassword | Not a valid password. |
| E_DAO_InvalidOperation | Can't perform this operation. |
| E_DAO_AccessDenied | No permission for the operation has been granted. |
| E_DAO_NotInTransaction | Commit or Rollback without BeginTrans. |
| E_DAO_OutOfMemory | There is insufficient memory for the task. |
| E_DAO_CantAllocatePage | Database has reached maximum size. |
| E_DAO_NoMoreCursors | Can't open any more tables or queries. |
| E_DAO_OutOfBuffers | There are not enough buffers for the task. |
| E_DAO_TooManyIndexes | Couldn't create an index. Too many indexes are already defined. |
| E_DAO_ReadVerifyFailure | Disk I/O error during read. |
| E_DAO_FilesysVersion | Can't open a database created with a previous version of the application. |
| E_DAO_NoMoreFiles | Out of MS-DOS file handles. |
| E_DAO_DiskError | Disk or network error. |
| E_DAO_InvalidPath | The path name specified isn't a valid path. |
| E_DAO_FileShareViolation | Couldn't use the specified database; file already in use. |
| E_DAO_FileLockViolation | Couldn't save the database; currently locked by another user. |
| E_DAO_RecordTooBig | Record is too large. |
| E_DAO_TooManyOpenDatabases | Can't open any more databases. |
| E_DAO_InvalidDatabase | Can't open the database. Your application might not recognize it, or the file might be corrupt. |
| E_DAO_FileLockingUnavailable | Couldn't lock file. |
| E_DAO_FileAccessDenied | Couldn't open file. |
| E_DAO_SharingBufferExceeded | MS-DOS file sharing lock count exceeded. You need to increase the number of locks installed with SHARE.EXE. |
| E_DAO_TaskLimitExceeded | Too many client tasks. |
| E_DAO_TooManyLongColumns | Too many Memo or OLE object fields. |
| E_DAO_InvalidFilename | Not a valid filename. |
| E_DAO_AbortSalvage | Couldn't repair this database. |
| E_DAO_LinkNotSupported | Operation isn't supported on attached (linked) tables. |
| E_DAO_NullKeyDisallowed | Index or primary key can't contain a null value. |
| E_DAO_OperationCanceled | The user canceled the operation. |
| E_DAO_QueryParmTypeMismatch | Wrong data type for the parameter. |
| E_DAO_QueryMissingParmsM | Too few parameters. Expected |. |
| E_DAO_QueryDuplicateAliasM | Duplicate output alias. |
| E_DAO_QueryDuplicateOutputM | Duplicate output destination. |
| E_DAO_QueryIsBulkOp | Can't open action query. |
| E_DAO_QueryIsNotBulkOp | Can't execute a nonaction query. |
| E_DAO_QueryNoOutputsM | Query or table must contain at least one output field. |
| E_DAO_QueryNoInputTablesM | Query input must contain at least one table or query. |
| E_DAO_QueryInvalidAlias | Not a valid alias name. |
| E_DAO_QueryInvalidBulkInputM | The action query can't be used as a row source. |
| E_DAO_QueryUnboundRef | Can't bind the name. |
| E_DAO_QueryExprEvaluation | Can't evaluate the expression. |
| E_DAO_EvalEBESErr | Error in the evaluation of the expression. |
| E_DAO_QueryNotUpdatable | Operation must use an updatable query. |
| E_DAO_TableRepeatInFromList | Can't repeat a table name in a FROM clause. |
| E_DAO_QueryExprSyntax | Syntax error in the expression. |
| E_DAO_QbeExprSyntax | Error in criteria expression. |
| E_DAO_FindExprSyntax | Find expression has a syntax error in the expression. |
| E_DAO_InputTableNotFound | Couldn't find the input table or query. |
| E_DAO_QueryAmbigRefM | Ambiguous field reference. |
| E_DAO_JoinTableNotInput | Joined table not listed in FROM clause. |
| E_DAO_UnaliasedSelfJoin | Can't join more than one table with the same name. |
| E_DAO_ColumnNotInJoinTable | JOIN operation refers to a nonjoined table. |
| E_DAO_QueryIsMGB | Can't use an internal report query. |
| E_DAO_QueryInsIntoBulkMGB | Can't insert data with an action query. |
| E_DAO_ExprUnknownFunctionM | Undefined function in the expression. |
| E_DAO_QueryCannotDelete | Couldn't delete from specified tables. |
| E_DAO_QueryTooManyGroupExprs | Too many expressions in a GROUP BY clause. |
| E_DAO_QueryTooManyOrderExprs | Too many expressions in an ORDER BY clause. |
| E_DAO_QueryTooManyDistExprs | Too many expressions in a DISTINCT output. |
| E_DAO_Column2ndSysMaint | Resultant table isn't allowed to have more than one Counter or Autonumber field. |
| E_DAO_HavingWOGrouping | HAVING clause without grouping or aggregation. |
| E_DAO_HavingOnTransform | Can't use the HAVING clause in a TRANSFORM statement. |
| E_DAO_OrderVsDistinct | ORDER BY clause conflicts with DISTINCT. |
| E_DAO_OrderVsGroup | ORDER BY clause conflicts with a GROUP BY clause. |
| E_DAO_AggregateInArgument | Can't have an aggregate function in the expression. |
| E_DAO_AggregateInWhere | Can't have an aggregate function in a WHERE clause. |
| E_DAO_AggregateInOrderBy | Can't have an aggregate function in an ORDER BY clause. |
| E_DAO_AggregateInGroupBy | Can't have an aggregate function in a GROUP BY clause. |
| E_DAO_AggregateInJoin | Can't have an aggregate function in a JOIN operation. |
| E_DAO_NullInJoinKey | Can't set a field in a join key to null. |
| E_DAO_ValueBreaksJoin | There is no record in the table with key matching field(s). |
| E_DAO_QueryTreeCycle | Circular reference caused by the parameter supplied. |
| E_DAO_OutputAliasCycle | Circular reference caused by an alias in the query definition's SELECT list. |
| E_DAO_QryDuplicatedFixedSetM | Can't specify a fixed column heading in a crosstab query more than once. |
| E_DAO_NoSelectIntoColumnName | Missing a destination field name in a SELECT INTO statement. |
| E_DAO_NoUpdateColumnName | Missing a destination field name in an UPDATE statement. |
| E_DAO_QueryNoInsertPerm | Record(s) can't be added; no insert data permission is on. |
| E_DAO_QueryNoReplacePerm | Record(s) can't be edited; no update data permission is on. |
| E_DAO_QueryNoDeletePerm | Record(s) can't be deleted; no delete data permission is on. |
| E_DAO_QueryNoReadDefPerm | Couldn't read definitions; there's no read design permission for the table or query. |
| E_DAO_QueryNoTblCrtPerm | Couldn't create; there's no create permission for the table or query. |
| E_DAO_QueryNoReadPerm | Record(s) can't be read; no read data permission is on. |
| E_DAO_QueryColNotUpd | Can't update; the field isn't updatable. |
| E_DAO_QueryLVInDistinct | Can't include a Memo or OLE object when you select unique values. |
| E_DAO_QueryLVInAggregate | Can't have a Memo or OLE object in an aggregate argument. |
| E_DAO_QueryLVInHaving | Can't have a Memo or OLE object in a criteria for an aggregate function. |
| E_DAO_QueryLVInOrderBy | Can't sort on a Memo or OLE object. |
| E_DAO_QueryLVInJoin | Can't join on a Memo or OLE object. |
| E_DAO_QueryLVInGroupBy | Can't group on a Memo or OLE object. |
| E_DAO_DotStarWithGrouping | Can't group on fields selected with *. |
| E_DAO_StarWithGrouping | Can't group on fields selected with *. |
| E_DAO_IllegalDetailRef | Argument isn't part of the aggregate function or grouping. |
| E_DAO_StarNotAtLevel0 | Can't use * in a crosstab query. |
| E_DAO_QueryInvalidMGBInput | Can't input from an internal report query. |
| E_DAO_InvalidName | Name supplied isn't a valid name. |
| E_DAO_QueryBadBracketing | Invalid bracketing of the name. |
| E_DAO_InsertIntoUnknownCol | INSERT INTO statement contains an unknown field name. |
| E_DAO_QueryNoDeleteTables | Must specify tables to delete from. |
| E_DAO_SQLSyntax | Invalid SQL statement; expected DELETE, INSERT, PROCEDURE, SELECT, or UPDATE. |
| E_DAO_SQLDeleteSyntax | Syntax error in a DELETE statement. |
| E_DAO_SQLFromSyntax | Syntax error in a FROM clause. |
| E_DAO_SQLGroupBySyntax | Syntax error in a GROUP BY clause. |
| E_DAO_SQLHavingSyntax | Syntax error in a HAVING clause. |
| E_DAO_SQLInsertSyntax | Syntax error in an INSERT statement. |
| E_DAO_SQLJoinSyntax | Syntax error in a JOIN operation. |
| E_DAO_SQLLevelSyntax | Syntax error in a LEVEL clause. |
| E_DAO_SQLMissingSemicolon | Missing semicolon (;) at end of an SQL statement. |
| E_DAO_SQLOrderBySyntax | Syntax error in an ORDER BY clause. |
| E_DAO_SQLParameterSyntax | Syntax error in a PARAMETER clause. |
| E_DAO_SQLProcedureSyntax | Syntax error in a PROCEDURE clause. |
| E_DAO_SQLSelectSyntax | Syntax error in a SELECT statement. |
| E_DAO_SQLTooManyTokens | Characters found after the end of an SQL statement. |
| E_DAO_SQLTransformSyntax | Syntax error in a TRANSFORM statement. |
| E_DAO_SQLUpdateSyntax | Syntax error in an UPDATE statement. |
| E_DAO_SQLWhereSyntax | Syntax error in a WHERE clause. |
| E_DAO_RmtSQLCError | ODBC: Call failed. |
| E_DAO_RmtDataOverflow | Not documented by Microsoft. |
| E_DAO_RmtConnectFailed | Not documented by Microsoft. |
| E_DAO_RmtIncorrectSqlcDll | Not documented by Microsoft. |
| E_DAO_RmtMissingSqlcDll | Not documented by Microsoft. |
| E_DAO_RmtConnectFailedM | ODBC: Connection to the datasource failed. |
| E_DAO_RmtDrvrVer | Not documented by Microsoft. |
| E_DAO_RmtSrvrVer | Not documented by Microsoft. |
| E_DAO_RmtMissingOdbcDll | ODBC: Couldn't find the DLL. |
| E_DAO_RmtInsertFailedM | ODBC: Insert failed on an attached (linked) table. |
| E_DAO_RmtDeleteFailedM | ODBC: Delete failed on an attached (linked) table. |
| E_DAO_RmtUpdateFailedM | ODBC: Update failed on an attached (linked) table. |
| E_DAO_RecordLocked | Couldn't save record; currently locked by another user. |
| E_DAO_InvalidBookmark | Not a valid bookmark. |
| E_DAO_TableNotOpen | Table isn't open. |
| E_DAO_DecryptFail | Couldn't decrypt the file. |
| E_DAO_NullInvalid | Null is invalid. |
| E_DAO_InvalidBufferSize | Couldn't perform the operation; the data is too long for the field. |
| E_DAO_ColumnNotUpdatable | Field can't be updated. |
| E_DAO_CantMakeINFFile | Couldn't open the .INF file. |
| E_DAO_MissingMemoFile | Missing memo file. |
| E_DAO_RecordDeleted | Record is deleted. |
| E_DAO_INFFileError | Invalid .INF file. |
| E_DAO_ExprIllegalType | Illegal type in the expression. |
| E_DAO_InstalIsamNotFound | Couldn't find the installable ISAM. |
| E_DAO_NoConfigParameters | Couldn't find the net path or user name. |
| E_DAO_CantAccessPdoxNetDir | Couldn't open PARADOX.NET. |
| E_DAO_NoMSysAccounts | Couldn't open the table MSysAccounts in the system database file. |
| E_DAO_NoMSysGroups | Couldn't open the table MSysGroups in the system database file. |
| E_DAO_DateOutOfRange | Date is out of range or is in an invalid format. |
| E_DAO_ImexCantOpenFile | Couldn't open the file. |
| E_DAO_ImexBadTableName | Not a valid table name. |
| E_DAO_ImexOutOfMemory | Not documented by Microsoft. |
| E_DAO_ImexEndofFile | Encountered an unexpected end of file. |
| E_DAO_ImexCantWriteToFile | Couldn't write to the file. |
| E_DAO_ImexBadRange | Invalid range. |
| E_DAO_ImexBogusFile | Invalid file format. |
| E_DAO_TempDiskFull | Not enough space on the temporary disk. |
| E_DAO_RmtLinkNotFound | Couldn't execute the query; couldn't find the attached (linked) table. |
| E_DAO_RmtTooManyColumns | SELECT INTO remote database tried to produce too many fields. |
| E_DAO_ReadConflictM | Couldn't save; currently locked by another user on a different machine. |
| E_DAO_CommitConflictM | Couldn't read; currently locked by another user on a different machine. |
| E_DAO_SessionWriteConflict | Couldn't update; currently locked by another session on this machine. |
| E_DAO_JetSpecialTableLocked | Table is exclusively locked by another user. |
| E_DAO_TooManyColumns | Too many fields are defined. |
| E_DAO_ColumnDuplicate | Can't define a field more than once. |
| E_DAO_OutputTableNotFound | Couldn't find the output table. |
| E_DAO_JetNoUserName | The user name is unknown. |
| E_DAO_JetNoMachineName | The machine name is unknown. |
| E_DAO_JetNoColumnName | The column name is unknown. |
| E_DAO_DatabaseInUse | Couldn't use the database; already in use. |
| E_DAO_DataHasChanged | Data has changed; operation was stopped. |
| E_DAO_TooManySessions | Couldn't start the session. Too many sessions are already active. |
| E_DAO_ReferenceNotFound | Couldn't find the reference. |
| E_DAO_IntegrityViolMasterM | Can't delete or change the record. Since related records exist in the table, referential integrity rules would be violated. |
| E_DAO_IntegrityViolSlaveM | Can't add or change the record. Referential integrity rules require a related record in the table. |
| E_DAO_ReadConflict | Couldn't save the database; currently locked by another user. |
| E_DAO_AggregatingHigherLevel | Can't specify a subquery in the expression. |
| E_DAO_DatabaseDuplicate | Database already exists. |
| E_DAO_QueryTooManyXvtColumn | Too many crosstab column headers. |
| E_DAO_SelfReference | Can't create a relationship between a field and itself. |
| E_DAO_CantUseUnkeyedTable | Operation isn't supported on a Paradox table with no primary key. |
| E_DAO_IllegalDeletedOption | Invalid deleted entry in the xBase section of the initialization setting. |
| E_DAO_IllegalStatsOption | Invalid stats entry in the xBase section of the initialization setting. |
| E_DAO_ConnStrTooLong | Connection string is too long. |
| E_DAO_TableInUseQM | Couldn't lock the table; currently in use. |
| E_DAO_JetSpecialTableInUse | Couldn't lock the specified table; currently in use by another user on a different machine. |
| E_DAO_IllegalDateOption | Invalid date entry in the xBase section of the initialization setting. |
| E_DAO_IllegalMarkOption | Invalid mark entry in the xBase section of the initialization setting. |
| E_DAO_BtrieveTooManyTasks | Too many Btrieve tasks. |
| E_DAO_QueryParmNotTableid | Parameter specified where a table name is required. |
| E_DAO_QueryParmNotDatabase | Parameter specified where a database name is required. |
| E_DAO_WriteConflict | Couldn't update; currently locked. |
| E_DAO_IllegalOperation | Invalid operation. |
| E_DAO_WrongCollatingSequence | Incorrect collating sequence. |
| E_DAO_BadConfigParameters | Invalid entries in the Btrieve section of the initialization setting. |
| E_DAO_QueryContainsDbParm | Query can't contain a database parameter. |
| E_DAO_QueryInvalidParmM | The parameter isn't a valid parameter name. |
| E_DAO_BtrieveDDCorrupted | Can't read the Btrieve data dictionary. |
| E_DAO_BtrieveDeadlock | Encountered record locking deadlock while performing a Btrieve operation. |
| E_DAO_BtrieveFailure | Errors encountered while using the Btrieve DLL. |
| E_DAO_IllegalCenturyOption | Invalid century entry in the xBase section of the initialization setting. |
| E_DAO_IllegalCollatingSeq | Invalid collating sequence. |
| E_DAO_NonModifiableKey | Btrieve: Can't change field. |
| E_DAO_ObsoleteLockFile | Out-of-date Paradox lock file. |
| E_DAO_RmtColDataTruncated | ODBC: Field would be too long; data truncated. |
| E_DAO_RmtCreateTableFailed | ODBC: Couldn't create the table. |
| E_DAO_RmtOdbcVer | Not documented by Microsoft. |
| E_DAO_RmtQueryTimeout | ODBC: Remote query time-out expired. |
| E_DAO_RmtTypeIncompat | ODBC: Data type isn't supported on the server. |
| E_DAO_RmtUnexpectedNull | Not documented by Microsoft. |
| E_DAO_RmtUnexpectedType | Not documented by Microsoft. |
| E_DAO_RmtValueOutOfRange | ODBC: Data is out of range. |
| E_DAO_TooManyActiveUsers | Too many active users. |
| E_DAO_CantStartBtrieve | Btrieve: Missing the Btrieve engine. |
| E_DAO_OutOfBVResources | Btrieve: Out of resources. |
| E_DAO_QueryBadUpwardRefedM | Invalid reference in the SELECT statement. |
| E_DAO_ImexNoMatchingColumns | None of the import field names match fields in the appended table. |
| E_DAO_ImexPasswordProtected | Can't import a password-protected spreadsheet. |
| E_DAO_ImexUnparsableRecord | Couldn't parse field names from the first row of the import table. |
| E_DAO_InTransaction | Operation isn't supported in transactions. |
| E_DAO_RmtLinkOutOfSync | ODBC: Linked table definition has changed. |
| E_DAO_IllegalNetworkOption | Invalid NetworkAccess entry in the initialization setting. |
| E_DAO_IllegalTimeoutOption | Invalid PageTimeout entry in the initialization setting. |
| E_DAO_CantBuildKey | Couldn't build the key. |
| E_DAO_FeatureNotAvailable | Operation isn't supported for this type of object. |
| E_DAO_IllegalReentrancy | Can't open a form whose underlying query contains a user-defined function that attempts to set or get the form's RecordsetClone property. |
| E_DAO_UNUSED | Not documented by Microsoft. |
| E_DAO_RmtDenyWriteIsInvalid | ODBC: Can't lock all records. |
| E_DAO_ODBCParmsChanged | Not documented by Microsoft. |
| E_DAO_INFIndexNotFound | Index file isn't found. |
| E_DAO_SQLOwnerAccessSyntax | Syntax error in the WITH OWNERACCESS OPTION declaration. |
| E_DAO_QueryAmbiguousJoins | Query contains ambiguous outer joins. |
| E_DAO_InvalidColumnType | Invalid field data type. |
| E_DAO_WriteConflictM | Couldn't update; currently locked by another user on a different machine. |
| E_DAO_TableLockedM | Not documented by Microsoft. |
| E_DAO_TableInUseMUQM | Not documented by Microsoft. |
| E_DAO_InvalidTableId | Invalid database object. |
| E_DAO_VtoNoFields | No fields defined. Can't append Tabledef or Index. |
| E_DAO_VtoNameNotFound | Item isn't found in this collection. |
| E_DAO_VtoFieldInCollection | Can't append. The field is part of a TableDefs collection. |
| E_DAO_VtoNotARecordset | Property can be set only when the field is part of a Recordset object's Fields collection. |
| E_DAO_VtoNoSetObjInDb | Can't set this property once the object is part of a collection. |
| E_DAO_VtoIndexInCollection | Can't append. The index is part of a TableDefs collection. |
| E_DAO_VtoPropNotFound | Property isn't found. |
| E_DAO_VtoIllegalValue | Invalid property value. |
| E_DAO_VtoNotArray | Object isn't a collection. |
| E_DAO_VtoNoSuchMethod | Method isn't applicable for this object. |
| E_DAO_NotExternalFormat | External table isn't in the expected format. |
| E_DAO_UnexpectedEngineReturn | Unexpected error from the external database driver. |
| E_DAO_InvalidDatabaseId | Invalid database ID. |
| E_DAO_TooManyKeys | Can't have more than 10 fields in an index. |
| E_DAO_NotInitialized | Database engine hasn't been initialized. |
| E_DAO_AlreadyInitialized | Database engine has already been initialized. |
| E_DAO_ColumnInUse | Can't delete a field that is part of an index or is needed by the system. |
| E_DAO_IndexInUse | Can't delete this index. It's either the current index or is used in a relationship. |
| E_DAO_TableNotEmpty | Can't create the field or index in a table that is already defined. |
| E_DAO_IndexHasPrimary | Primary key already exists. |
| E_DAO_IndexDuplicate | Index already exists. |
| E_DAO_IndexInvalidDef | Invalid index definition. |
| E_DAO_WrongMemoFileType | Format of the memo file doesn't match the specified external database format. |
| E_DAO_ColumnCannotIndex | Can't create an index on the given field. |
| E_DAO_IndexHasNoPrimary | Paradox index isn't primary. |
| E_DAO_DDLConstraintSyntax | Syntax error in a CONSTRAINT clause. |
| E_DAO_DDLCreateTableSyntax | Syntax error in a CREATE TABLE statement. |
| E_DAO_DDLCreateIndexSyntax | Syntax error in a CREATE INDEX statement. |
| E_DAO_DDLColumnDefSyntax | Syntax error in field definition. |
| E_DAO_DDLAlterTableSyntax | Syntax error in an ALTER TABLE statement. |
| E_DAO_DDLDropIndexSyntax | Syntax error in a DROP INDEX statement. |
| E_DAO_DDLDropSyntax | Syntax error in a DROP TABLE or DROP INDEX. |
| E_DAO_V11NotSupported | Join expression isn't supported. |
| E_DAO_ImexNothingToImport | Couldn't import the table or query. No records were found, or all records contain errors. |
| E_DAO_RmtTableAmbiguous | There are several tables with this name. Specify owner in the format owner.table. |
| E_DAO_JetODBCConformanceError | ODBC specification conformance error. This error should be reported to the ODBC driver vendor. |
| E_DAO_IllegalRelationship | Can't create a relationship. |
| E_DAO_DBVerFeatureNotAvailable | Can't perform this operation. Features in this version aren't available in databases with older formats. |
| E_DAO_RulesLoaded | Can't change a rule while the rules for this table are in use. |
| E_DAO_ColumnInRelationship | Can't delete this field. It's part of one or more relationships. |
| E_DAO_InvalidPin | You must enter a personal identifier (PID) consisting of at least four and no more than 20 characters and digits. |
| E_DAO_RmtBogusConnStr | Invalid connection string in pass-through query. |
| E_DAO_SingleColumnExpected | At most, one field can be returned from a subquery that doesn't use the EXISTS keyword. |
| E_DAO_ColumnCountMismatch | The number of columns in the two selected tables or queries of a union query don't match. |
| E_DAO_InvalidTopArgumentM | Invalid TOP argument in a select query. |
| E_DAO_PropertyTooLarge | Property setting can't be larger than 2K. |
| E_DAO_JPMInvalidForV1x | This property isn't supported for external data sources or for databases created in a previous version. |
| E_DAO_PropertyExists | Property specified already exists. |
| E_DAO_TLVNativeUserTablesOnly | Validation rules and default values can't be placed on system or attached (linked) tables. |
| E_DAO_TLVInvalidColumn | Can't place this validation expression on this field. |
| E_DAO_TLVNoNullM | Field can't contain a null value. |
| E_DAO_TLVNoBlankM | Field can't be a zero-length string. |
| E_DAO_TLVRuleViolationM | Not documented by Microsoft. |
| E_DAO_TLVRuleVioNoMessage | One or more values entered is prohibited by the validation rule set for the field. |
| E_DAO_QueryTopNotAllowedM | Top not allowed in delete queries. |
| E_DAO_SQLUnionSyntax | Syntax error in a union query. |
| E_DAO_TLVExprSyntaxM | Syntax error in a table-level validation expression. |
| E_DAO_NoDbInConnStr | No database is specified in the connection string or IN clause. |
| E_DAO_QueryBadValueListM | Crosstab query contains one or more invalid fixed column headings. |
| E_DAO_QueryIsNotRowReturning | Query can't be used as a row source. |
| E_DAO_QueryIsDDL | Query is a DDL query and can't be used as a row source. |
| E_DAO_SPTReturnedNoRecords | Pass-through query with ReturnsRecords property set to TRUE didn't return any records. |
| E_DAO_QueryIsSnapshot | Recordset isn't updatable. |
| E_DAO_QueryExprOutput | Field is based on an expression and can't be edited. |
| E_DAO_QueryTableRO | Table is read-only. |
| E_DAO_QueryRowDeleted | Record in table was deleted by another user. |
| E_DAO_QueryRowLocked | Record in table is locked by another user. |
| E_DAO_QueryFixupChanged | To make changes to this field, first save the record. |
| E_DAO_QueryCantFillIn | Can't enter a value into a blank field on the "one" side of an outer join. |
| E_DAO_QueryWouldOrphan | Records in the table would have no record on the "one" side. |
| E_DAO_V10Format | Can be present only in version 1.0 format. |
| E_DAO_InvalidDelete | DeleteOnly called with a nonzero cbData. |
| E_DAO_IllegalIndexDDFOption | Btrieve: Invalid IndexDDF option in the initialization setting. |
| E_DAO_IllegalDataCodePage | Invalid DataCodePage option in the initialization setting. |
| E_DAO_XtrieveEnvironmentError | Btrieve: Xtrieve options aren't correct in the initialization setting. |
| E_DAO_IllegalIndexNumberOption | Btrieve: Invalid IndexDeleteRenumber option in the initialization setting. |
| E_DAO_QueryIsCorruptM | Query is corrupt. |
| E_DAO_IncorrectJoinKeyM | Current field must match the join key on the "one" side of the outer join because it has been updated. |
| E_DAO_QueryLVInSubqueryM | Invalid Memo or OLE object in the subquery. |
| E_DAO_InvalidDatabaseM | Unrecognized database format. |
| E_DAO_TLVCouldNotBindRef | Unknown or invalid reference in the validation expression or a default value in the table. |
| E_DAO_CouldNotBindRef | Unknown or invalid field reference. |
| E_DAO_QueryWrongNumDestCol | Number of query values and destination fields aren't the same. |
| E_DAO_QueryPKeyNotOutput | Can't add record(s); the primary key for the table isn't in the recordset. |
| E_DAO_QueryJKeyNotOutput | Can't add record(s); the join key of the table isn't in the recordset. |
| E_DAO_NumericFieldOverflow | Numeric field overflow. |
| E_DAO_InvalidObject | Object is invalid for the operation. |
| E_DAO_OrderVsUnion | ORDER BY expression uses nonoutput fields. |
| E_DAO_NoInsertColumnNameM | No destination field name in an INSERT INTO statement. |
| E_DAO_MissingDDFFile | Btrieve: Can't find the file FIELD.DDF. |
| E_DAO_SingleRecordExpected | At most, one record can be returned by this subquery. |
| E_DAO_DefaultExprSyntax | Syntax error in default value. |
| E_DAO_ExclusiveDBConflict | Database is opened by the user specified on the specified machine. |
| E_DAO_QueryIsNotDDL | Query isn't a properly formed data-definition query. |
| E_DAO_SysDatabaseOpenError | Can't open the Microsoft Jet engine system database. |
| E_DAO_SQLInvalidSPT | Pass-through query must contain at least one character. |
| E_DAO_QueryTooComplex | Query is too complex. |
| E_DAO_SetOpInvalidInSubquery | Unions aren't allowed in a subquery. |
| E_DAO_RmtMultiRowUpdate | Single-row update/delete affected more than one row of an attached (linked) table. The unique index contains duplicate values. |
| E_DAO_QueryNoJoinedRecord | Record(s) can't be added; there's no corresponding record on the "one" side. |
| E_DAO_QueryLVInSetOp | Can't use a Memo or OLE object field in a SELECT clause of a union query. |
| E_DAO_VtoInvalidOnRemote | Property value isn't valid for REMOTE objects. |
| E_DAO_VtoNoFieldsRel | Can't append a relation with no fields defined. |
| E_DAO_VtoObjectInCollection | Can't append. The object is already in the collection. |
| E_DAO_DDLDiffNumRelCols | Relationship must be on the same number of fields with the same data types. |
| E_DAO_DDLIndexColNotFound | Can't find the field in the index definition. |
| E_DAO_DDLPermissionDenied | Can't modify the table's design. It's in a read-only database. |
| E_DAO_DDLObjectNotFound | Can't find the table or constraint. |
| E_DAO_DDLIndexNotFound | No such index on the table. |
| E_DAO_DDLNoPkeyOnRefdTable | Can't create the relationship. The referenced table doesn't have a primary key. |
| E_DAO_DDLColumnsNotUnique | Specified fields aren't uniquely indexed in the table. |
| E_DAO_DDLIndexDuplicate | Table already has an index with the same name. |
| E_DAO_DDLTableNotFound | Table doesn't exist. |
| E_DAO_DDLRelNotFound | No such relationship in the table. |
| E_DAO_DDLRelDuplicate | There is already a relationship named in the current database. |
| E_DAO_DDLIntegrityViolation | Can't create relationships to enforce referential integrity. Existing data in the table violates referential integrity rules with a related table. |
| E_DAO_DDLColumnDuplicate | Field already exists in the table. |
| E_DAO_DDLColumnNotFound | No field is named in the table. |
| E_DAO_DDLColumnTooBig | The size of the field is too long. |
| E_DAO_DDLColumnInRel | Can't delete the field. It's part of one or more relationships. |
| E_DAO_VtoCantDeleteBuiltIn | Can't delete a built-in property. |
| E_DAO_VtoUDPsDontSupportNull | User-defined properties don't support a Null value. |
| E_DAO_VtoMissingRequiredParm | Property must be set before using this method. |
| E_DAO_JetJetInitInvalidPath | Can't find the TEMP directory. |
| E_DAO_TLVExprUnknownFunctionM | Unknown function in the validation expression or default value. |
| E_DAO_QueryNotSupported | Query support unavailable. |
| E_DAO_AccountDuplicate | Account name already exists. |
| E_DAO_JetwrnPropCouldNotSave | An error has occurred. Properties weren't saved. |
| E_DAO_RelNoPrimaryIndexM | There is no primary key in the table. |
| E_DAO_QueryKeyTooBig | Can't perform a join, group, sort, or indexed restriction. A value being searched or sorted on is too long. |
| E_DAO_PropMustBeDDL | Can't save the property because it's a schema property. |
| E_DAO_IllegalRIConstraint | Invalid referential integrity constraint. |
| E_DAO_RIViolationMasterCM | Can't perform a cascading operation. Since related records exist in the table, referential integrity rules would be violated. |
| E_DAO_RIViolationSlaveCM | Can't perform a cascading operation. There must be a related record in the table. |
| E_DAO_RIKeyNullDisallowedCM | Can't perform a cascading operation. It would result in a null key in the table. |
| E_DAO_RIKeyDuplicateCM | Can't perform a cascading operation. It would result in a duplicate key in the table. |
| E_DAO_RIUpdateTwiceCM | Can't perform a cascading operation. It would result in two updates on fields in the table. |
| E_DAO_RITLVNoNullCM | Can't perform a cascading operation. It would cause a field to become null, which isn't allowed. |
| E_DAO_RITLVNoBlankCM | Can't perform a cascading operation. It would cause a field to become a zero-length string, which isn't allowed. |
| E_DAO_RITLVRuleViolationCM | Can't perform a cascading operation. Caused by the fact that there are related records in another table, and referential integrity rules would be violated. |
| E_DAO_RITLVRuleVioCNoMessage | Can't perform a cascading operation. The value entered is prohibited by the validation rule set. |
| E_DAO_TLVRuleEvalEBESErr | Error in the validation rule. |
| E_DAO_TLVDefaultEvalEBESErr | Error in the default value. |
| E_DAO_BadMSysConf | The server's MSysConf table exists, but it's in an incorrect format. Contact your system administrator. |
| E_DAO_TooManyFindSessions | Too many FastFind sessions were invoked. |
| E_DAO_InvalidColumnM | Invalid field name in the definition of the index or relationship. |
| E_DAO_REPReadOnly | Not documented by Microsoft. |
| E_DAO_RIInvalidBufferSizeCM | Invalid entry. Can't perform the cascading operation specified in the table because the value entered is too big for the field. |
| E_DAO_RIWriteConflictCM | Not documented by Microsoft. |
| E_DAO_JetSpecialRIWriteConflictCM | Can't perform a cascading update on the table because it's currently in use by another user on a different machine. |
| E_DAO_RISessWriteConflictCM | Can't perform a cascading update on the table because it's currently in use. |
| E_DAO_NoBlank | Zero-length string is valid only in a text or Memo field. |
| E_DAO_FutureError | Not documented by Microsoft. |
| E_DAO_QueryInvalidBulkInput | An action query can't be used as a row source. |
| E_DAO_NetCtrlMismatch | Can't open the specified table. Another user has the table open using a different network control file or locking style. |
| E_DAO_4xTableWith3xLocking | Can't open this Paradox 4.x or 5.x table because ParadoxNetStyle is set to 3.x in the initialization setting. |
| E_DAO_VtoObjectNotSet | Object is invalid or not set. |
| E_DAO_VtoDataConvError | Data type conversion error. |
All the error codes that appear in Table 13.8 are from DBDAOERR.H. You can edit this file and create an intelligent error handler if you want by creating a large select/case selection block. Of course, you can elect not to handle the errors that aren't applicable to your application to keep your error handler's size within reason.
Table 13.8 lists the members of the CDaoException class.
| Member | Description |
| Data Members | |
| m_scode | The SCODE value associated with the error. See Table 13.7 for a list of the valid SCODE values. |
| m_nAfxDaoError | Contains the extended error code for errors that occur in the MFC DAO classes. |
| m_pErrorInfo | Contains a pointer to the CDaoErrorInfo object that will contain information about one DAO error object. |
| Construction | |
| CDaoException() | Constructs the CDaoException object. |
| Operations | |
| GetErrorCount() | Returns a count of how many errors are in the Microsoft Jet database engine's errors collection. |
| GetErrorInfo() | Returns error information about a particular error object, specified by the nIndex parameter, from the errors collection. |
The CDaoFieldExchange class is used to transfer data from fields in a result set to the CDaoRecordset member variables. You need to use this class only if you're going to write data exchange routines for custom data types. If you're only using standard data types, you won't need to use the CDaoFieldExchange object. This process, called DFX, manages the exchange in both directions from the result set and to the result set.
NOTE
Technical Note 53 (in Visual C++ Books Online, see Visual C++ Books, MFC 4.0, MFC Technical Notes) has an example of how to write DFX routines.
Like other features of DAO, the design and usage of the DAO record field exchange (DFX) is based on the same model as ODBC's record field exchange (RFX). If you're comfortable with ODBC's RFX, you'll find it easy to use DAO's DFX.
The CDaoFieldExchange object is used to provide the context information that DAO needs for the record field exchange. The CDaoFieldExchange object supports a number of operations, including binding parameters and field data members and setting various flags (null, dirty, and so on) on fields in the current record. The DFX operations are performed on CDaoRecordset data members defined by the enum FieldType in CDaoFieldExchange. Possible FieldType values are
You use the IsValidOperation() member when you're going to write your own (custom) DFX functions. You do this by using the SetFieldType() member function, which is often done in your CDaoRecordset::DoFieldExchange functions.
Table 13.9 lists the members of the CDaoFieldExchange class.
| Member | Description |
| Data Members | |
| m_nOperation | Holds the current DFX operation being performed. |
| m_prs | Holds a pointer to the current CDaoRecordset on which the DFX operation is being performed. |
| Member Functions | |
| IsValidOperation() | Returns a zero if the current operation isn't appropriate for the type of field being updated. |
| SetFieldType() | Sets the type of CDaoRecordset data member that is to be represented until the next call to SetFieldType(). |
The CDaoRecordView class is used to display database records using a dialog box template. This class, derived from CFormView (which is in turn derived from CScrollView, and so on), is virtually identical to ODBC's CRecordView.
The view presented by CDaoRecordView is connected directly to a CDaoRecordset object. As with CRecordView, you create a dialog box (usually with AppWizard) and locate appropriate dialog controls to display fields from the datasource. The CDaoRecordView object uses standard dialog data exchange (DDX) and DAO record field exchange (DFX) to actually move the record's data to and from the CDaoRecordView dialog box's controls. CDaoRecordView will also supply the default implementation for record navigation so that you can easily implement moves to the first, next, previous, or last record in the data source. CDaoRecordView also provides the interface for updating the record currently in view.
Most programmers (at least the nonmasochistic ones) will use AppWizard to create the shell for their DAO database application. If you don't use AppWizard, you'll find it rather difficult to create MFC Windows applications. The most common way to create your record view is with AppWizard. AppWizard creates both the record view class and its associated recordset class as part of your skeleton starter application.
You can use ClassWizard to add a CDaoRecordView later in the development process if necessary. However, before starting your application, you should decide what the application's user interface will look like.
When you use AppWizard to create your application's shell, you will be provided with toolbar buttons that the user will be able to use for record navigation. These AppWizard-supplied buttons let the user make the next, previous, first, or last record the current record.
The CDaoRecordView class maintains the current record's position in the recordset. The buttons for record navigation are enabled and disabled to prevent the user from making incorrect choices, such as attempting to select the previous record when the first record in the recordset is the current record.
Table 13.10 lists the members of the CDaoRecordView class.
| Member | Description |
| Construction | |
| CDaoRecordView | Constructs the CDaoRecordView object. |
| Attributes | |
| OnGetRecordset() | Provides a pointer to an object derived from CDaoRecordset. When you're using ClassWizard, this function is automatically overridden, and a CDaoRecordset object is created automatically for you if necessary. |
| IsOnLastRecord() | Returns zero if the current record isn't the last record in the associated recordset. |
| IsOnFirstRecord() | Returns zero if the current record isn't the first record in the associated recordset. |
| Operations | |
| OnMove() | Moves to the specified record, first updating the current record with any changes that have been made. The specified record may be next, previous, first, or last. |
DAO is new to Visual C++ programmers. Although Visual Basic has offered DAO support for some time, Visual C++ programmers have had to work with ODBC, which doesn't offer the same capabilities as DAO. Visual Basic programmers have had a substantial advantage when working with Access database files.
DAO is managed using a set of MFC classes. These classes are similar to the MFC ODBC classes, but there are some differences. The MFC DAO classes can either directly or indirectly access all of the functionality of the Microsoft DAO/Access Jet Database Engine. The MFC DAO database classes presented in this chapter include
CDaoDatabase
CDaoException
CDaoFieldExchange
CDaoQueryDef
CDaoRecordset
CDaoRecordView
CDaoTableDef
CDaoWorkspace
Each class was discussed, and the members of each class were described. This chapter also listed the errors that CDaoException handles.
