Fluent mapping inheritance

Question

I have an issue I don't know the best solution for. Hopefully someone here can help =)

What I'm trying to solve: We have to type of users in a system, person and organization. I want to have a shared login table for the two (ie the user probably won't know which type of user they are, they just relate to username and password). So I've created a login table for usernames and passwords. But I need to know who the login is connected to, so I need a reference to either person or organization.

Consider the following classes (simplified):

public class Login
{
    public string Username {get; set;}
    public string Password {get;set;}
}

public class LoginPerson : Login
{
    public Person Person {get;set;}
}

public class LoginOrg : Login
{
    public Organization Organization {get;set;}
}

public class Person
{
    public LoginPerson LoginPerson {get;set;}
    //Lots of other properties. Removed for simplicity
}

public class Organization
{
    public LoginOrg LoginOrg {get;set;}
    //Lots of other properties. Removed for simplicity
}

The person configuration is set up as follows:

public class PersonConfiguration : EntityTypeConfiguration<Person>
    {
        public PersonConfiguration()
        {
            HasRequired(p => p.LoginPerson).WithRequiredPrincipal(p => p.Person);
        }
    }

First of all, this doesn't work. I get an exception saying "System.Data.EntityCommandCompilationException: System.Data.EntityCommandCompilationException: An error occurred while preparing the command definition. See the inner exception for details. ---> System.Collections.Generic.KeyNotFoundException: The given key was not present in the dictionary.." So my first question is why doesn't this work? My second question is: which strategy is best suited for this kind of inheritance? TPT, TPH or TPC?

score 1 · Answer 1 · answered Aug 29 '13 at 18:05

Well, for starters, none of your entities have keys. You need a primary key to make them work. EF uses a convention to do this, which is the class name plus Id at the end, like PersonId, or you key be explicit with an attribute of [Key]

Second, your model is confusing and fairly circular. And without primary keys, there's no way to to create associations.

I'm confused about why you have a member that is a LoginPerson in a Person object, and the same for an Organization? In any event, you really need to rethink this model and figure out what your keys are.

Sorry about not including the primary keys. I removed them when I simplified the classes. All classes has an Id column which is a PK. The circular reference is intentional, as they are navigational properties. However, I solved the exception issue. And my second question can be answered by google =) — Zaphod, Aug 30 '13 at 06:45

Zaphod · Accepted Answer · 2013-08-30T09:19:52.367

The solution to my exception was to set up the correct configuration ;-) PersonConfiguration didn't need to include any configuration for the LoginPerson property. I added a LoginPersonConfiguration ->

public class LoginPersonConfiguration : EntityTypeConfiguration<LoginPerson>
{
    public LoginPersonConfiguration()
    {
        ToTable("LoginPerson");
        HasKey(l => l.Id);
        HasRequired(l => l.Person).WithOptional(p => p.LoginPerson).Map(t => t.MapKey("PersonId")); 
    }
}

And I also had to add the Login to the DbContext class

public class MyDbContext : DbContext
{
    public DbSet<Person> Persons { get; set; }
    public DbSet<Login> Logins { get; set; }
}

When it comes to which strategy is best, I have decided to go for TPT.

Fluent mapping inheritance

2 Answers2