Moq - mocking entity framework sets generically

Question

I'm looking at using Moq for mocking my Entity Framework data context, and i'm currently using the EntityFramework.Testing library to help. I have the below code:

var set = new Mock<DbSet<Blog>>().SetupData(data);
var context = new Mock<BloggingContext>();
context.Setup(c => c.Blogs).Returns(set.Object);

However, I want to create a generic method that takes the entity type and automatically sets it up. So something like the below

    public void SetupData<T>(List<T> items) where T : class
    {
        var set = new Mock<DbSet<T>>().SetupData(items);
        var context = new Mock<BloggingContext>();
        context.Setup(c => c.Set<T>()).Returns(set.Object);
    }

However, my mocking the generic 'Set' object, the data context objects are still null - ie dataContext.Blogs

Is there some way I can use reflection or an expression to find the correct set object on the data context based on the type, and set that up to return my mocked set?

Thanks!

Answer 1

I think before mocking a method of a third-party library, we need to take a look at its source code.

DbContext.Set calls InternalContext.Set , please take a look on the source code :

    public virtual IInternalSetAdapter Set(Type entityType)
    {
        entityType = ObjectContextTypeCache.GetObjectType(entityType);

        IInternalSetAdapter set;
        if (!_nonGenericSets.TryGetValue(entityType, out set))
        {
            // We need to create a non-generic DbSet instance here, which is actually an instance of InternalDbSet<T>.
            // The CreateInternalSet method does this and will wrap the new object either around an existing
            // internal set if one can be found from the generic sets cache, or else will create a new one.
            set = CreateInternalSet(
                entityType, _genericSets.TryGetValue(entityType, out set) ? set.InternalSet : null);
            _nonGenericSets.Add(entityType, set);
        }
        return set;
    }

As you can see, it tries to find value from a private dictionary _nonGenericSets , I think this is why it returns null when you directly get value from DbContext.Blogs .

Don't forget that you only mocked Set method, not non-generic DBSets. If you are going to use what you have mocked, you should use it like below:

// context.Set<Blog>()