Transaction and concurrency

When ORM methods are invoked without any transaction, all the data is committed to the database when the ORM session is flushed. ORM session is flushed whenORMFlush()is called or if autoflush is enabled when the request ends.

This works fine when there is not much concurrency, however in most practical scenarios you would need to use transaction in your application so that the data in your database is always in a consistent state.

With ColdFusion ORM, you can manage transactions in the following two ways:

• Using Hibernate transaction: User has full control and ColdFusion does not intervene. The application has to flush/close the session and commit/rollback the transaction.

  For more information on transactions, go to the following URL:

  http://community.jboss.org/wiki/sessionsandtransactions

• Using CFTransaction: ColdFusion manages the transaction. Since a transaction cannot be distributed (across different data sources), application must ensure that the changes made in the transaction affect only one Hibernate session. That is, only one data source.

  ColdFusion allows reading of data from other sessions (data source) in a transaction but changes must be made in only one session. Multiple dirty sessions at any time in the transaction can result in exceptions and the transaction is rolled back. Before transaction begins, all existing sessions in the request are flushed. The previous session (if any) is reused.

  When the transaction is committed, the dirty session is automatically flushed (before committing the transaction). When the transaction is rolled back, the changed session cannot be used any longer because it can cause rolled back data to get committed later. Therefore, the session participating in the transaction is cleared when transaction is rolled back.

A description of transaction is beyond the scope of this document. For more information on transactions, see the hibernate documentation.

To run the ORM methods inside a transaction, they must be inside<cftransaction>. A simple example snippet of using ORM with<cftransaction>is as follows:

Because we have not called commit on the<cftransaction>specifically, it is automatically committed when the<cftransaction>ends.

All<cftransaction>semantics including savepoint, multiple rollbacks, multiple commits, and nested transactions work with ORM. You can also have both queries and ORM in the same<cftransaction>.

When<cftransaction>begins, any existing ORM session is flushed and closed, and a new ORM session is created. The<cftransaction>can be committed or rolled back using appropriate ColdFusion tags in<cftransaction>. When the transaction ends and has not been committed or rolled back explicitly, it is automatically committed and the ORM session is closed. If there is any error inside the transaction, without any exception handling, the transaction is rolled back.

For more details on<cftransaction>, see the CFML Reference Guide.