Workspace.BeginTrans method (DAO)
Applies to: Access 2013, Office 2013
Begins a new transaction. Read/write Database.
expression A variable that represents a Workspace object.
The transaction methods BeginTrans, CommitTrans, and Rollback manage transaction processing during a session defined by a Workspace object. You use these methods with a Workspace object when you want to treat a series of changes made to the databases in a session as one unit.
Typically, you use transactions to maintain the integrity of your data when you must both update records in two or more tables and ensure changes are completed (committed) in all tables or none at all (rolled back). For example, if you transfer money from one account to another, you might subtract an amount from one and add the amount to another. If either update fails, the accounts no longer balance. Use the BeginTrans method before updating the first record, and then, if any subsequent update fails, you can use the Rollback method to undo all of the updates. Use the CommitTrans method after you successfully update the last record.
Within one Workspace object, transactions are always global to the Workspace and aren't limited to only one Connection or Database object. If you perform operations on more than one connection or database within a Workspace transaction, resolving the transaction (that is, using the CommitTrans or Rollback method) affects all operations on all connections and databases within that workspace.
After you use CommitTrans, you can't undo changes made during that transaction unless the transaction is nested within another transaction that is itself rolled back. If you nest transactions, you must resolve the current transaction before you can resolve a transaction at a higher level of nesting.
If you want to have simultaneous transactions with overlapping, non-nested scopes, you can create additional Workspace objects to contain the concurrent transactions.
If you close a Workspace object without resolving any pending transactions, the transactions are automatically rolled back.
If you use the CommitTrans or Rollback method without first using the BeginTrans method, an error occurs.
Some ISAM databases used in a Microsoft Access workspace may not support transactions, in which case the Transactions property of the Database object or Recordset object is False. To make sure the database supports transactions, check the value of the Transactions property of the Database object before using the BeginTrans method. If you are using a Recordset object based on more than one database, check the Transactions property of the Recordset object.
If a Recordset is based entirely on Microsoft Access database engine tables, you can always use transactions. Recordset objects based on tables created by other database products, however, may not support transactions. For example, you can't use transactions in a Recordset based on a Paradox table. In this case, the Transactions property is False. If the Database or Recordset doesn't support transactions, the methods are ignored and no error occurs.
You can't nest transactions if you are accessing ODBC data sources through the Microsoft Access database engine.
In ODBC workspaces, when you use CommitTrans your cursor may no longer be valid. Use the Requery method to view the changes in the Recordset, or close and re-open the Recordset.
- You can often improve the performance of your application by breaking operations that require disk access into transaction blocks. This buffers your operations and may significantly reduce the number of times a disk is accessed.
- In a Microsoft Access workspace, transactions are logged in a file kept in the directory specified by the TEMP environment variable on the workstation. If the transaction log file exhausts the available storage on your TEMP drive, the database engine triggers a run-time error. At this point, if you use CommitTrans, an indeterminate number of operations are committed, but the remaining uncompleted operations are lost, and the operation has to be restarted. Using a Rollback method releases the transaction log and rolls back all operations in the transaction.
- Closing a clone Recordset within a pending transaction will cause an implicit Rollback operation.
The following example shows how to use a transaction in a Data Access Objects (DAO) workspace.
Sample code provided by the Microsoft Access 2010 Programmer’s Reference.
Public Sub TransferFunds() Dim wrk As DAO.Workspace Dim dbC As DAO.Database Dim dbX As DAO.Database Set wrk = DBEngine(0) Set dbC = CurrentDb Set dbX = wrk.OpenDatabase("e:\books\acc2007vba\myDB.accdb") On Error GoTo trans_Err 'Begin the transaction wrk.BeginTrans 'Withdraw funds from one account table dbC.Execute "INSERT INTO tblAccounts ( Amount, Txn, TxnDate ) SELECT -20, 'DEBIT', Date()", dbFailOnError 'Deposit funds into another account table dbX.Execute "INSERT INTO tblAccounts ( Amount, Txn, TxnDate ) SELECT 20, 'CREDIT', Date()", dbFailOnError 'Commit the transaction wrk.CommitTrans dbForceOSFlush trans_Exit: 'Clean up wrk.Close Set dbC = Nothing Set dbX = Nothing Set wrk = Nothing Exit Sub trans_Err: 'Roll back the transaction wrk.Rollback Resume trans_Exit End Sub