Entity Framework Table splitting


Example

And now let's say you want to do the opposite of entity splitting: instead of mapping one entity into two tables, you would like to map one table into two entities. This is called table splitting. Let's say you have one table with five columns: PersonId, Name, AddressLine, City, ZipCode, where PersonId is the primary key. And then you would like to create an EF model like this:

public class Person  
{
  public int PersonId { get; set; }
  public string Name { get; set; }
  public Address Address { get; set; }
}

public class Address  
{        
  public string ZipCode { get; set; }
  public string City { get; set; }
  public string AddressLine { get; set; }
  public int PersonId { get; set; }
  public Person Person { get; set; }
}

One thing jumps right out: there is no AddressId in Address. That's because the two entities are mapped to the same table, so they must have the same primary key as well. If you do table splitting, this is something you just have to deal with. So besides table splitting, you also have to configure the Address entity and specify the primary key. And here's how:

public class MyDemoContext : DbContext  
{
  public DbSet<Person> Products { get; set; }
  public DbSet<Address> Addresses { get; set; }

  protected override void OnModelCreating(DbModelBuilder modelBuilder)
  {
     modelBuilder.Entity<Address>().HasKey(t => t.PersonId);
     modelBuilder.Entity<Person>().HasRequired(t => t.Address)
                                  .WithRequiredPrincipal(t => t.Person);

     modelBuilder.Entity<Person>().Map(m => m.ToTable("People"));
     modelBuilder.Entity<Address>().Map(m => m.ToTable("People"));
  }
}