Disable AutoCommit using C# Mysql Connector after an unhandled exception

Question

I'm currently developing a C# application with MySql as backend database.

Unfortunately I found a wired behaviour I can't explain.

I wanted to use transactions, to "combine" multiple queries to make sure only all commands or none are executed.

However, because of a coding error by me, an unhandled exception occured during the transaction.

My understanding of a transaction is, that in such a case, the transaction is rolled back.

Nevertheless I found out that Mysql seems to enable AutoCommit by default and commits after the disconnect because of the crash resulting from the unhandled exception.

So I tried to disable it by executing SET autocommit = 0

But this doesn't work.

EDIT: I created the transaction using following code:

_transaction = _mysqlConnection.BeginTransaction();
MySqlCommand cmd = new MySqlCommand();
cmd.Connection = _mysqlConnection;
cmd.Transaction = _transaction

Other people mentioned, that the usage of BEGIN should solve this issue, but this isn't the case. In the Mysql log the following querys are executed:

239 Connect   user@localhost on gssm
239 Query     SHOW VARIABLES
239 Query     SHOW COLLATION
239 Query     SET character_set_results=NULL
239 Init DB   db
239 Query     SET autocommit = 0
239 Query     SET SESSION TRANSACTION ISOLATION LEVEL REPEATABLE READ
239 Query     BEGIN
239 Query     INSERT INTO TestTable (KeyField, Value) VALUES ('foo', 'bar')

Of course I should fix my code, so that no unhandled exception occurs, but is there a way to prevent Mysql from doing this?

Thanks!

Chris

Answer 1

It is a good idea, to use a MySql Engine that actually supports Transactions... MyISAM does not, which was the problem. So if want to use transactions make sure, that you use the right engine (InnoDB for example).

Sorry for your waste and time and thank you for your suggestions.

Chris

Answer 2

have you tried manually starting the session

START TRANSACTION;

after

SET autocommit =0;

Good Luck!

Answer 3

Did you manually rollback the transaction on your exception handler?

catch(Exception ex)
{
    try
    {
        trans.Rollback();
    }
    catch(MySqlException mse)
    {
        log.error(mse);
    }
}

Answer 4

You aren't actually creating a transaction in that log, see the MySQL transaction docs for more info how that would look. BEGIN just starts a compound set of statements.

If you're using ADO.NET, the simplest way to accomplish this is just create a new DbTransaction with the correct commit/rollback semantics.