Unable to initiate lock

[IT]

I have a forward only model mapped entirely using Fluent, and I'm trying to lock a collection without success.

There aren't many examples out there, and few posts in the forum.

Here's an example of how I'm setting up:-

BackendConfiguration backendConfiguration = new BackendConfiguration();
backendConfiguration.Backend = "mssql";
Meta2.Context context = new Meta2.Context(connectionString, backendConfiguration);

Then I'm trying something like this:-

context.Scope.TransactionProperties.Concurrency = TransactionMode.PESSIMISTIC_EXPLICIT;
context.Scope.Transaction.Begin();
context.Scope.Transaction.Lock(context.Scope.Extent<Accounts.Payable.Invoice>(), LockMode.WRITE);

But I get "Telerik.OpenAccess.Exceptions.TransactionException: Transaction properties cannot be modified for active transactions." trying to set the concurrency. So I try a commit just before, to close the transaction:

context.Scope.Transaction.Commit();
context.Scope.TransactionProperties.Concurrency = TransactionMode.PESSIMISTIC_EXPLICIT;
context.Scope.Transaction.Begin();
context.Scope.Transaction.Lock(context.Scope.Extent<Accounts.Payable.Invoice>(), LockMode.WRITE);

Now I get: "Telerik.OpenAccess.Exceptions.TransactionException: The method Commit is not supported for managed transactions."

OK.. I'll try flush then...

context.Scope.Transaction.Flush();
context.Scope.TransactionProperties.Concurrency = TransactionMode.PESSIMISTIC_EXPLICIT;
context.Scope.Transaction.Begin();
context.Scope.Transaction.Lock(context.Scope.Extent<Accounts.Payable.Invoice>(), LockMode.WRITE);

Now I get: "Telerik.OpenAccess.OpenAccessException: no active transaction"... hey?? didn't it just say there *was* a transaction?

Usually I have a context I generate in a HttpModule, however trying using a new scope as in the example above makes no difference.

Has anyone got a working example for this scenario?

Currently using ORM 2011.2.713, but doesn't seem version dependent.

[Jan Blessenohl]

Hi Aleks,
You are right, this is a little tricky. The context starts a transaction immediately. This makes it impossible to change it later. You have to change the default for all contexts first.

using (var ctx = new EntitiesModel())
{
    ctx.Scope.Database.DefaultTransactionProperties.Concurrency = TransactionMode.PESSIMISTIC_EXPLICIT;
}
using (var ctx = new EntitiesModel())
{
    foreach (var item in ctx.A_types)
    {
        ctx.Scope.Transaction.Lock(item, LockMode.DELETE);
    }
}

Be careful in multithreadding environments, maybe you have to put this into a locking block. Here is a second way, maybe the better one:

using (var ctx = new EntitiesModel())
{
    using (var tmp = new EntitiesModel())
    {
        var old = tmp.Scope.Database.DefaultTransactionProperties.Concurrency;
        tmp.Scope.Database.DefaultTransactionProperties.Concurrency = TransactionMode.PESSIMISTIC_EXPLICIT;
        var s = ctx.Scope;// this works because the real scope is generated lazy
        tmp.Scope.Database.DefaultTransactionProperties.Concurrency = old;
    }
    foreach (var item in ctx.A_types)
    {
        ctx.Scope.Transaction.Lock(item, LockMode.DELETE);
    }
}

Kind regards,
Jan Blessenohl
the Telerik team