Entity Framework 6 Code First Fluent API Table Mapping

Question

I have a table in an existing database that looks something like this:

PK
FK
Col1
Col2
Col3
Col4
Col5

I need to get it into a class hierarchy like this:

public abstract class BaseClass : Entity
{
    public int PK {get; set;}
    public string Col1 {get; set;}
}

public class Child1 : BaseClass
{
    public string Col2 {get; set;}
    public string Col3 {get; set;}
}

public class Child2 : BaseClass
{
    public string Col4 {get; set;}
    public string Col5 {get; set;}
}

I am currently using the Fluent API to configure the entities like so:

public abstract class BaseClassConfig<TEntity> : EntityTypeConfiguration<TEntity> where TEntity : Entity
{
    public BaseClassConfig()
    {
        ToTable("TheTableName");
        HasKey(x => x.Id);

        Property(x => x.Col1).HasColumnName("SomeName");
    }
}

public class Child1Config : BaseClassConfig<Child1>
{
    public Child1Config()
    {
        Property(x => x.Col2).HasColumnName("SomeName");
        Property(x => x.Col3).HasColumnName("SomeName");
    }
}

public class Child2Config : BaseClassConfig<Child2>
{
    public Child2Config()
    {
        Property(x => x.Col4).HasColumnName("SomeName");
        Property(x => x.Col5).HasColumnName("SomeName");
    }
}

When I added these to the context the inherits from DbContext :

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
    modelBuilder.Configurations.Add(new Child1Config());
    modelBuilder.Configurations.Add(new Child2Config());
}

I get the following error:

The entity types 'Child1' and 'Child2' cannot share table 'TheTableName' because they are not in the same type hierarchy or do not have a valid one to one foreign key relationship with matching primary keys between them.

I had a look at this article: http://www.asp.net/mvc/overview/getting-started/getting-started-with-ef-using-mvc/implementing-inheritance-with-the-entity-framework-in-an-asp-net-mvc-application

But it does not really talk about using the fluent api to configure the types, rather directly adding them to the context via DbSet<> .

How do I setup a single table to map to different classes through a base class using the fluent api?

Answer 1

A good reference I turn to a lot is this MSDN article: Configuring/Mapping Properties and Types with the Fluent API

In it you'll see a reference to the Table-Per-Hierarchy (TPH) Inheritance pattern. Essentially what you are missing is a discriminator field (and based on the error, the FK is also not mapped).

By default, the discriminator column is called Discriminator , but as you can see from the article, this can be customized in the code-first mapping:

modelBuilder.Entity<Course>()  
    .Map<Course>(m => m.Requires("Type").HasValue("Course"))  
    .Map<OnsiteCourse>(m => m.Requires("Type").HasValue("OnsiteCourse"));

In the above example, Type is the discriminator which allows EF to know which entity type to materialize ie entity Course when Type == "Course" .