Does Entity Framework Code First allow for fluent mappings in separate files?

Question

I am developing a rather large database schema using Entity Framework Code First. I prefer the Fluent API over the Data Annotations approach, as it leaves my domain objects as simple POCOs.

In order to use Fluent API, I have to override OnModelCreating in the class that inherits from DbContext.

I don't like that all mappings for all of my entities are in this one method. I have used things like FluentNHibernate before, where each entity has it's own mapping class. Does EF have anything similar?

I suppose I could create my own interface to implement a mapping class and call them all within the OnModelCreating method. I could use reflection or an IoC to discover them all. I don't particularly see anything wrong with this approach, but I was wondering if Entity Framework already comes with something like this out of the box?

Answer 1

You can create one configuration class per entity derived from EntityTypeConfiguration<TEntity> and put these classes into separate files. In your derived DbContext you add instances of those configuration classes to the model builder. Example:

public class UserConfiguration : EntityTypeConfiguration<User>
{
    public UserConfiguration()
    {
        HasKey(u => u.UserName);

        Property(u => u.UserName)
            .HasMaxLength(50)
            .IsRequired();

        // etc.
    }
}

public class RoleConfiguration : EntityTypeConfiguration<Role>
{
    public RoleConfiguration()
    {
        HasKey(r => r.RoleName);

        // etc.
    }
}

Derived context:

public class MyContext : DbContext
{
    //...

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        modelBuilder.Configurations.Add(new UserConfiguration());
        modelBuilder.Configurations.Add(new RoleConfiguration());
    }
}

There is also a ComplexTypeConfiguration<T> you can derive from to configure complex types.