CDaoRecordset::Edit
Call this member function to allow changes to the current record.
virtual void Edit( );
Remarks
Once you call the Edit member function, changes made to the current record's fields are copied to the copy buffer. After you make the desired changes to the record, call Update to save your changes. Edit saves the values of the recordset's data members. If you call Edit, make changes, then call Edit again, the record's values are restored to what they were before the first Edit call.
警告
If you edit a record and then perform any operation that moves to another record without first calling Update, your changes are lost without warning. In addition, if you close the recordset or the parent database, your edited record is discarded without warning.
In some cases, you may want to update a column by making it Null (containing no data). To do so, call SetFieldNull with a parameter of TRUE to mark the field Null; this also causes the column to be updated. If you want a field to be written to the data source even though its value has not changed, call SetFieldDirty with a parameter of TRUE. This works even if the field had the value Null.
The framework marks changed field data members to ensure they will be written to the record on the data source by the DAO record field exchange (DFX) mechanism. Changing the value of a field generally sets the field dirty automatically, so you will seldom need to call SetFieldDirty yourself, but you might sometimes want to ensure that columns will be explicitly updated or inserted regardless of what value is in the field data member. The DFX mechanism also employs the use of PSEUDO NULL. For more information, see CDaoFieldExchange::m_nOperation.
If the double-buffering mechanism is not being used, then changing the value of the field does not automatically set the field as dirty. In this case, it will be necessary to explicitly set the field dirty. The flag contained in m_bCheckCacheForDirtyFields controls this automatic field checking.
When the recordset object is pessimistically locked in a multiuser environment, the record remains locked from the time Edit is used until the updating is complete. If the recordset is optimistically locked, the record is locked and compared with the pre-edited record just before it is updated in the database. If the record has changed since you called Edit, the Update operation fails and MFC throws an exception. You can change the locking mode with SetLockingMode.
注意
Optimistic locking is always used on external database formats, such as ODBC and installable ISAM.
The current record remains current after you call Edit. To call Edit, there must be a current record. If there is no current record or if the recordset does not refer to an open table-type or dynaset-type recordset object, an exception occurs. Calling Edit causes a CDaoException to be thrown under the following conditions:
There is no current record.
The database or recordset is read-only.
No fields in the record are updatable.
The database or recordset was opened for exclusive use by another user.
Another user has locked the page containing your record.
If the data source supports transactions, you can make the Edit call part of a transaction. Note that you should call CDaoWorkspace::BeginTrans before calling Edit and after the recordset has been opened. Also note that calling CDaoWorkspace::CommitTrans is not a substitute for calling Update to complete the Edit operation. For more information about transactions, see class CDaoWorkspace.
For related information, see the topics "AddNew Method", "Edit Method", "Delete Method", "Update Method", and "Updatable Property" in DAO Help.
Requirements
Header: afxdao.h