Tag Archives: in memory

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)
        {

            modelBuilder.Entity<EntityType1>().HasData(
                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:

context.Database.EnsureCreated();

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.

References

https://github.com/dotnet/efcore/issues/11666

https://github.com/dotnet/efcore/issues/6872

Manually Adding DbContext for an Integration Test

In EF Core, there is an extension method that allows you to add a DBContext, called AddDBContext. This is a really useful method, however, in some cases, you may find that it doesn’t work for you. Specifically, if you’re trying to inject a DBContext to use for unit testing, it doesn’t allow you to access the DBContext that you register.

Take the following code:

services.AddDbContext<MyDbContext>(options =>
                options.UseSqlServer());
         

I’ve previously written about using UseInMemoryDatabase. However, this article covered unit tests only – that is, you are able to instantiate a version of the DBContext in the unit test, and use that.

As a reminder of the linked article, if you were to try to write a test that included that DBContext, you might want to use an in memory database; you might, therefore, build up a DBContextOptions like this:

var options = new DbContextOptionsBuilder<MyDbContext>()
                .UseInMemoryDatabase(Guid.NewGuid().ToString())
                .EnableSensitiveDataLogging()
                .Options;
var context = new MyDbContext(options);

But in a scenario where you’re writing an integration test, you may need to register this with the IoC. Unfortunately, in this case, AddDbContext can stand in your way. The alternative is that you can simply register the DbContext yourself:

var options = new DbContextOptionsBuilder<MyDbContext>()
                .UseInMemoryDatabase(Guid.NewGuid().ToString())
                .EnableSensitiveDataLogging()
                .Options;
var context = new MyDbContext(options);
AddMyData(context);
services.AddScoped<MyDbContext>(_ => context);

AddMyData just adds some data into your database; for example:

private void AddTestUsers(MyDbContext context)
{            
    MyData data = new MyData()
    {
        value1 = "test",
        value2 = "1"                
    };
    context.MyData.Add(subject);
    context.SaveChanges();
}

This allows you to register your own, in memory, DbContext in your IoC.