Control over BeginTransaction in AdoTransaction

[greenlight2k]

It should be possible to control how the DbTransaction is created for generic Database Drivers.

Firebird for example implements its own DbConnection: FbConnection.
In this class, there is a Firebird specific overload for the BeginTransaction Method that lets you use specific Firebird FbTransactionOptions.

Of course, there is no way for NHibernate to consider such generic implementations.

I have a suggestion for giving the User an optional control over this matter:

Inside AdoTransaction on the Method Begin(IsolationLevel isolationLevel) there is the following code where the DbTransaction is created:

if (isolationLevel == IsolationLevel.Unspecified)
{
  trans = session.Connection.BeginTransaction();
}
else
{
  trans = session.Connection.BeginTransaction(isolationLevel);
}

How about moving that code to a protected virtual Method like this:

protected virtual DbTransaction BeginTransaction(IsolationLevel isolationLevel, ISessionImplementor sessionImplementor)
{
    if (isolationLevel == IsolationLevel.Unspecified)
    {
        return sessionImplementor.Connection.BeginTransaction();
    }
    else
    {
        return sessionImplementor.Connection.BeginTransaction(isolationLevel);
    }
}

And changing the mentioned code above using that Method:

trans = BeginTransaction(isolationLevel, session);

This way, i can derive from AdoTransaction and override my own specific implementation.
For example with the specific Firebird Wait Option:

public class FirebirdAdoTransaction : AdoTransaction
{
    public FirebirdAdoTransaction(ISessionImplementor session) : base(session)
    {
    }

    protected override DbTransaction BeginTransaction(IsolationLevel isolationLevel, ISessionImplementor sessionImplementor)
    {
        if (sessionImplementor.Connection is FbConnection firebird)
        {
            var transactionOptions = new FbTransactionOptions
            {
                TransactionBehavior = FbTransactionBehavior.Wait
            };

            if (isolationLevel == IsolationLevel.ReadCommitted)
            {
                transactionOptions.TransactionBehavior |= FbTransactionBehavior.ReadCommitted;
            }

            return firebird.BeginTransaction(transactionOptions);
        }
        else
        {
            return base.BeginTransaction(isolationLevel, sessionImplementor);
        }
    }
}

Then, i only have to create my own TransactionFactory, using the FirebirdAdoTransaction and change my NHibernate Settings "transaction.factory_class" to this Factory:

public class FirebirdTransactionFactory : AdoNetWithSystemTransactionFactory
{
    public override ITransaction CreateTransaction(ISessionImplementor session)
    {
        return new FirebirdAdoTransaction(session);
    }
}

I think this is a good addition in general, since you never know what generic implementation of DbConnection is used by the Database driver and this protected virtual method gives the user full control over driver related transaction options.

Also: No breaking change.

EDIT:
Changed the name of the protected virtual method to BeginTransaction like suggested by hazzik

[hazzik]

Sounds good.

[hazzik]

Let's name this protected virtual method as BeginTransaction to be consistent with the ADO.

[fredericDelaporte]

@greenlight2k, would you contribute this BeginTransaction with a PR? It is likely it could then be merged soon.

[fredericDelaporte]

The overridable method has been put in the DriverBase class. It will be added to the IDriver interface in NHibernate 6.0.

So in NHibernate v5.2, the feature is available when using a driver deriving from DriverBase. Override the DriverBase.BeginTransaction method.

Drivers are meant to handle the data provider specificities, and so they are the right place to handle the need as expressed here. (Maybe the Firebird example here is even something that should be put in current NHibernate Firebird driver.)