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entity-framework-4concurrency

Locking before save with fixed concurrencymode

I'm learning about concurrency in conjunction with EF4.0 and have a question about the locking pattern used.

Say I configure a fixed concurrency mode on a version number property.

Now say I fetch a record (entity) from the database (context) and edit some property. Version gets incremented and when SaveChanges is called on its context. If the current database (context) version matches the version of the original record (entity) the save continues, otherwise an OptimisticConcurrencyException gets thrown by EF.

Now, my point of interest is the following: between the check of the versions there's always a small period of time, however small, it is there. So in theory someone else could've just updated the record between the comparison and the actual save, thus possibly corrupting the data.

How does this get solved? It feels as if the problem just gets pushed forward.

Solution

  • There is no period of time between checking versions and updating record because the database command looks like:

    UPDATE SomeTable
SET SomeColumn = 'SomeValue'
WHERE Id = @Id AND Version = @OldVersion

SELECT @@ROWCOUNT

    The check and update is one atomic operation. Rowcount will return 0 if no record with Id = @Id and Version = @OldVersion exists and that zero is translated to the exception.