Entity Framework 4.1 The model backing the context has changed since the database was created, immediately after creating DB

Question

I am working on a project which uses Entity Framework 4.1 for persisting our various objects to the database (code first).

I am testing in Visual Studio with a local SQL Express DB, and our Jenkins server deploys committed code to a testing server. When this happens I temporarily change my local connection string to point to the testing DB server and run a unit test to re-create the test database so that it matches our latest entities, etc.

I've recently noticed our testing server is giving this error:

The model backing the 'EntityFrameworkUnitOfWork' context has changed since the database was created. Either manually delete/update the database, or call Database.SetInitializer with an IDatabaseInitializer instance. For example, the DropCreateDatabaseIfModelChanges strategy will automatically delete and recreate the database, and optionally seed it with new data.

This is usually an indication that our code has changed and I need to run the unit test to re-create the database. Except I just did that! I don't believe there is anything wrong with our deployment process - the DLLs on the test server seem to be the same versions as in my local environment. Are there any other settings or environment factors that can cause this error about the model having changed since the database was created?

I'm new here - thanks for any help!

Answer 1

The error you see means that the model hash stored in EdmMetadata table is different from the model hash computed from the model in the application. Because you are running database creation from a different application (your dev. application) it is possible that those two differ. Simple advice here is: don't use different applications for database creation and instead let your main application create the database (either automatically or for example with some admin interface).

As another option you should be able to turn off this check completely by removing the convention responsible for these checks:

modelBuilder.Conventions.Remove<IncludeMetadataConvention>(); 

Model hash computation is dependent on current entities in your application (any simple change result in different model hash) and on database server versions / manifest. For example a model deployed on SQL server 2005 and 2008 will have different model hash (Express vs. Full or 2008 vs. 2008 R2 should not result in different model hash).

Answer 2

This can happen due to reflection ordering differences across different platforms. To verify, you can use the EdmxWriter API to compare the EDMX from both environments. If any of the tables have different column ordering, then this is the issue.

To workaround, you can change the way your test database gets updated such that it is updated from your test server rather than your local box.

We are going to fix this issue in the next release.