CDaoRecordset Class

Статья
10/16/2008

Represents a set of records selected from a data source.

class CDaoRecordset : public CObject

Заметки

Known as "recordsets," CDaoRecordset objects are available in the following three forms:

Table-type recordsets represent a base table that you can use to examine, add, change, or delete records from a single database table.
Dynaset-type recordsets are the result of a query that can have updateable records. These recordsets are a set of records that you can use to examine, add, change, or delete records from an underlying database table or tables. Dynaset-type recordsets can contain fields from one or more tables in a database.
Snapshot-type recordsets are a static copy of a set of records that you can use to find data or generate reports. These recordsets can contain fields from one or more tables in a database but cannot be updated.

Each form of recordset represents a set of records fixed at the time the recordset is opened. When you scroll to a record in a table-type recordset or a dynaset-type recordset, it reflects changes made to the record after the recordset is opened, either by other users or by other recordsets in your application. (A snapshot-type recordset cannot be updated.) You can use CDaoRecordset directly or derive an application-specific recordset class from CDaoRecordset. You can then:

Scroll through the records.
Set an index and quickly look for records using Seek (table-type recordsets only).
Find records based on a string comparison: "<", "<=", "=", ">=", or ">" (dynaset-type and snapshot-type recordsets).
Update the records and specify a locking mode (except snapshot-type recordsets).
Filter the recordset to constrain which records it selects from those available on the data source.
Sort the recordset.
Parameterize the recordset to customize its selection with information not known until run time.

Class CDaoRecordset supplies an interface similar to that of class CRecordset. The main difference is that class CDaoRecordset accesses data through a Data Access Object (DAO) based on OLE. Class CRecordset accesses the DBMS through Open Database Connectivity (ODBC) and an ODBC driver for that DBMS.

Примечание.
The DAO database classes are distinct from the MFC database classes based on Open Database Connectivity (ODBC). All DAO database class names have the "CDao" prefix. You can still access ODBC data sources with the DAO classes; the DAO classes generally offer superior capabilities because they are specific to the Microsoft Jet database engine.

You can either use CDaoRecordset directly or derive a class from CDaoRecordset. To use a recordset class in either case, open a database and construct a recordset object, passing the constructor a pointer to your CDaoDatabase object. You can also construct a CDaoRecordset object and let MFC create a temporary CDaoDatabase object for you. Then call the recordset's Open member function, specifying whether the object is 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.

Use the object's member functions and data members to scroll through the records and operate on them. The operations available depend on whether the object is a table-type recordset, a dynaset-type recordset, or a snapshot-type recordset, and whether it is updateable or read-only — this depends on the capability of the database or Open Database Connectivity (ODBC) data source. To refresh records that may have been changed or added since the Open call, call the object's Requery member function. Call the object's Close member function and destroy the object when you finish with it.

CDaoRecordset uses DAO record field exchange (DFX) to support reading and updating of record fields through type-safe C++ members of your CDaoRecordset or CDaoRecordset-derived class. You can also implement dynamic binding of columns in a database without using the DFX mechanism using GetFieldValue and SetFieldValue.

For related information, see the topic "Recordset Object" in DAO Help.