Starts a database transaction.
Assembly: System.Data (in System.Data.dll)
This command maps to the SQL Server implementation of BEGIN TRANSACTION.
You must explicitly commit or roll back the transaction using the Commit or Rollback method. To make sure that the .NET Framework Data Provider for SQL Server transaction management model performs correctly, avoid using other transaction management models, such as the one provided by SQL Server.
If you do not specify an isolation level, the default isolation level is used. To specify an isolation level with the BeginTransaction method, use the overload that takes the iso parameter (BeginTransaction). The isolation level set for a transaction persists after the transaction is completed and until the connection is closed or disposed. Setting the isolation level to Snapshot in a database where the snapshot isolation level is not enabled does not throw an exception. The transaction will complete using the default isolation level.
If a transaction is started and a level 16 or higher error occurs on the server, the transaction will not be rolled back until the Read method is invoked. No exception is thrown on ExecuteReader.
When your query returns a large amount of data and calls BeginTransaction, a SqlException is thrown because SQL Server does not allow parallel transactions when using MARS. To avoid this problem, always associate a transaction with the command, the connection, or both before any readers are open.
For more information on SQL Server transactions, see "Explicit Transactions" and "Coding Efficient Transactions" in SQL Server Books Online.