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Wednesday, February 4, 2015

Entity Framework (EF) TransactionScope vs Database.BeginTransaction

Entity Framework (EF) TransactionScope vs Database.BeginTransaction

In today blog post we will talk a little about a new feature that is available on EF6+ related to Transactions.
Until now, when we had to use transaction we used ‘TransactionScope’. It works great and I would say that is something that is now in our blood.
using (var scope = new TransactionScope(TransactionScopeOption.Required)) 
            { 
                using (SqlConnection conn = new SqlConnection("...")) 
                { 
                    conn.Open(); 
                    SqlCommand sqlCommand = new SqlCommand(); 
                    sqlCommand.Connection = conn; 
                    sqlCommand.CommandText = ...
                    sqlCommand.ExecuteNonQuery(); 
 
                    ...
                }  
                scope.Complete(); 
            }
Starting with EF6.0 we have a new way to work with transactions. The new approach is based on Database.BeginTransaction(), Database.Rollback(), Database.Commit(). Yes, no more TransactionScope.
In the following example we create a new transaction and use it to commit our changes.
using (var dbContextTransaction = context.Database.BeginTransaction()) 
                { 
                    try 
                    { 
                        context.Foo.Add(foo);
                        context.Foo.Add(foo);
                        context.SaveChanges();
                        dbContextTransaction.Commit(); 
                    } 
                    catch (Exception) 
                    { 
                        dbContextTransaction.Rollback(); 
                    } 
                } 
The new feature allow us to pass an existing transaction between different context and even reuse an existing transaction using Database.UseTransaction().
using (var context = new FooContext(conn, contextOwnsConnection: false)) 
                        { 
                           context.Database.UseTransaction(myTransaction); 
         context.Foo.Add(foo);
                           context.SaveChanges(); 
                        } 
 
                        myTransaction.Commit(); 
The next tables shows what are the features supported by the new way to execute transaction in comparison with the old one.
Property
Database.BeginTransaction
(new feature)
TransactionScope
(old feature)
Is recommended by Microsoft in EF6
Yes
No
Only database related operation in transaction
Yes
No
Mixing DB operation and C# code in the transaction
No
Yes
Wrap Database.ExecuteSqlCommand in transaction if no transaction is specified
Yes
No
Can specify to a new DataContext an existing transaction that will be used
Yes
No
Can be database connection managed manually and specified to objects
Yes (to DataContext)
Partially Yes
Can the isolation level to be controlled
Yes
Yes
Can execute pure SQL queries in a custom transaction
Yes
Yes
Async calls supported in a transaction
Yes
Yes (from .NET 4.5.1, with some small limitation)
Where the transaction is managed and controlled
By developer from code
In background, by the .NET Core
Full control of the transaction
Yes
Partially
Existing transaction can be used
Yes
No

There is limitation related to retry policy. When we are doing multiple SaveChanges to our contexts, the retry policy would not know what data was saved or not. See below example:
using (var db = new FooContext()) 
{ 
    using (var transaction = db.Database.BeginTransaction()) 
    { 
        db.Foos.Add(new Foo()); 
        db.SaveChanges(); 
 
        db.Foos.Add(new Foo()); 
        db.SaveChanges(); 
 
        transaction.Commit(); 
    } 
}
In this case we have a workaround by suspending the retry execution strategy for that peace of code or specify a manual call execution strategy. I highly recommend to review this situations and try to create a store procedure that execute all the necessary changes in one transaction. It is safer and can be controlled easier.
The new way of using transactions is the one that is recommended by EF Team. This is the way how we should use transactions.

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