Unit Testing EF Core – How to Invoke the Contents of OnModelCreating

In this post, I wrote about how you can test an EF Database, using an InMemory database.

I’m guessing a few people reading this will be thinking this is stating the bloody obvious, but it certainly wasn’t to me. Imagine you have a DBContext with some seed data; for example:

        protected override void OnModelCreating(ModelBuilder modelBuilder)

                new EntityType1
                    Id = "1",
                    Name = "Test1",
                    Description = "Testing",
                    IsTest = true,
                    SomeNumber = 1

In the above linked article, this seed data will never fire; however, simply calling:


Once the context is created, will force the migrations to be run inside the in-memory instance, and you should end up with a system mirroring what you would see, should you run this migration against a physical database.

Caveat Emptor

When using this against EF Core 2.2 I found, what appeared to be, this issue. The error being, while I was trying to insert a record, an error returned saying that an item with the same key exists on the table. However, no such item should exist. The linked article seems to imply that this relates to a bug with the insert for the in-memory database, and that it is resolved for EF Core 3.0. I haven’t validated this, so it may, or may not work to upgrade to EF Core 3.0. Please add a comment if you can validate or negate this.




1 thought on “Unit Testing EF Core – How to Invoke the Contents of OnModelCreating

  1. Micha

    thanks for the article.
    I think that context.Database.EnsureCreated() does not apply migrations. This is the job of context.Database.Migrate().

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