Entity Framework DB-First, implement inheritance

Question

I'm trying to implement inheritance using entity framework 6.0 and database first approach. OK, let's say I have a Person and an Organization entity like below:

// a simplified version of organization entity
public class Organization
{
    public Guid ID { get; set; }
    public string Nickname { get; set; }
    public string Email { get; set; }
    public string PhoneNumber { get; set; }
    public string OfficialName { get; set; }
    public Guid CEOID { get; set; }
    public DateTime? RegisterDate { get; set; }
}

// a simplified version of person entity
public class Person
{
    public Guid ID { get; set; }
    public string Nickname { get; set; }
    public string Email { get; set; }
    public string PhoneNumber { get; set; }
    public Guid PersonID { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public string MiddleName { get; set; }
    public string NationalCode { get; set; }
    public DateTime? BirthDate { get; set; }
}

I can create these two tables in database, but I want to use inheritance so the fields which is repeated in both Person and Organization could be in another base class like below:

public class Identity
{
    // These fields are the common fields between Person and Organization
    public Guid ID { get; set; }
    public string Nickname { get; set; }
    public string Email { get; set; }
    public string PhoneNumber { get; set; }
}

How can I achieve this in db-first approach?

Michalmichalak

Answer 1

One possible way is to use one table for each type called TPT (table-per-type), which I prefer to use. To achieve this, you define your tables like the model shown in the following picture:

Note that the relationships between child and base entity are one-to-one on their pk columns, and all common fields are moved to the base table. After creating your tables, right click on the models page in your visual studio, and select Update Model from Database..., and then in the add tab, select these 3 tables to add. At first you should see this model diagram, which needs to be changed a bit:

Do these steps for Person and Organization separately:

• Right click on entity and select Properties
• In the Base Type property select Identity
• Select and then delete the association between this entity and Identity
• Select and then Delete the PK (ID column) of this entity (Inherits from base entity)

After these steps save your model. Now your model should look like this:

Now compile your project and enjoy your life!

Additional resources:
Entity Framework Designer TPH Inheritance

Michalmichalak

TPH just means 1 table per base class and some masking to only select columns related to the base and subclass properties of a specific class. There's a lot less joins, but a bunch of sparsely populated columns. – Burgee

I get an error about my foreign key from the child table to the PK in the parent table. Insufficient mapping: Foreign key must be mapped to some AssociationSet or EntitySets participating in a foreign key association on the conceptual side. I believe we deleted that in your 3rd bullet step. Any ideas? Does it really need to be deleted? The error goes away if I don't delete it, but I'm not sure if it actually works at runtime yet. – Nyala

If I remove the association I get the error "An Association or inheritance relationship needs to be created to enforce this constraint.(...). Keeping the one-to-one association worked perfectly for me! Thanks – Bedelia