Transaction: How Transactions Affect Updates (ODBC)
Updates to the data source are managed during transactions through the use of an edit buffer (the same method used outside of transactions). The field data members of a recordset collectively serve as an edit buffer that contains the current record, which the recordset backs up temporarily during an AddNew or Edit. During a Delete operation, the current record is not backed up within a transaction. For more information about the edit buffer and how updates store the current record, see Recordset: How Recordsets Update Records (ODBC).
Note
If you have implemented bulk row fetching, you cannot call AddNew, Edit, or Delete. You must instead write your own functions to perform updates to the data source. For more information about bulk row fetching, see Recordset: Fetching Records in Bulk (ODBC).
During transactions, AddNew, Edit, and Delete operations can be committed or rolled back. The effects of CommitTrans and Rollback might cause the current record to not be restored to the edit buffer. To make sure that the current record is properly restored, it is important to understand how the CommitTrans and Rollback member functions of CDatabase work with the update functions of CRecordset.
How CommitTrans Affects Updates
The following table explains the effects of CommitTrans on transactions.
How CommitTrans Affects Updates
| Operation | Status of data source |
|---|---|
AddNew and Update, and then CommitTrans |
New record are added to data source. |
AddNew (without Update), and then CommitTrans |
New record is lost. Record not added to data source. |
Edit and Update, and then CommitTrans |
Edits committed to data source. |
Edit (without Update), and then CommitTrans |
Edits to the record are lost. Record remains unchanged on the data source. |
Delete then CommitTrans |
Records deleted from data source. |
How Rollback Affects Transactions
The following table explains the effects of Rollback on transactions.
How Rollback Affects Transactions
| Operation | Status of current record | You must also | Status of data source |
|---|---|---|---|
AddNew and Update, then Rollback |
Content of the current record is stored temporarily to make room for new record. New record is entered into edit buffer. After Update is called, the current record is restored to the edit buffer. |
Addition to data source made by Update is reversed. |
|
AddNew (without Update), then Rollback |
Content of the current record is stored temporarily to make room for new record. Edit buffer contains new record. | Call AddNew again to restore the edit buffer to an empty, new record. Or call Move(0) to restore the old values to the edit buffer. |
Because Update was not called, there were no changes made to the data source. |
Edit and Update, then Rollback |
An unedited version of the current record is stored temporarily. Edits are made to the content of the edit buffer. After Update is called, the unedited version of the record is still temporarily stored. |
Dynaset: Scroll off the current record then back to restore the unedited version of the record to the edit buffer. Snapshot: Call Requery to refresh the recordset from the data source. |
Changes to data source made by Update are reversed. |
Edit (without Update), then Rollback |
An unedited version of the current record is stored temporarily. Edits are made to the content of the edit buffer. | Call Edit again to restore the unedited version of the record to the edit buffer. |
Because Update was not called, there were no changes made to the data source. |
Delete then Rollback |
Content of the current record is deleted. | Call Requery to restore the content of the current record from the data source. |
Deletion of data from data source is reversed. |
See also
Transaction (ODBC)
Transaction: Performing a Transaction in a Recordset (ODBC)
CDatabase Class
CRecordset Class