ProfK ProfK - 8 days ago 6
SQL Question

Database in use error with Entity Framework 4 Code First

I have an MVC3 and EF 4 Code First application, which is configured to change the DB when the model changes, by setting the DB Initializer to a

DropCreateDatabaseIfModelChanges<TocratesDb>
, where
TocratesDb
is my derived
DbContext
.

I have now made a change to the model, by adding properties to a class, but when EF tries to drop and recreate the DB, I get the following error:

Cannot drop database "Tocrates" because it is currently in use.


I have absolutely no other connections anywhere open on this database. I assume that my cDbContext still has an open connection to the database, but what can I do about this?

NEW: Now my problem is how to re-create the database based on the model. By using the more general IDatabaseInitializer, I lose that and have to implement it myself.

Answer

Your current context must have an opened connection to be able to drop the database. The problem is that there can be other opened connections which will block your db initializer. One very nice example is having opened any table from your database in management studio. Another possible problem can be opened connections in the connection pool of your application.

In MS SQL this can be avoided for example by switching DB to SINGLE USER mode and forcing all connections to be closed and incomplete transactions rolled back:

ALTER DATABASE Tocrates SET SINGLE_USER WITH ROLLBACK IMMEDIATE

You can create a new intializer which will first call this command and then drops the database. Be aware that you should handle a database connection by yourselves because ALTER DATABASE and DROP DATABASE must be called on the same connection.

Edit:

Here you have example using Decorator pattern. You can modify it and initialize inner initializer inside the constructor instead of passing it as a parameter.

public class ForceDeleteInitializer : IDatabaseInitializer<Context>
{
    private readonly IDatabaseInitializer<Context> _initializer;

    public ForceDeleteInitializer(IDatabaseInitializer<Context> innerInitializer)
    {
        _initializer = innerInitializer;    
    }

    public void InitializeDatabase(Context context)
    {
        context.Database.SqlCommand("ALTER DATABASE Tocrates SET SINGLE_USER WITH ROLLBACK IMMEDIATE");
        _initializer.InitializeDatabase(context);
    }
}
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