Lerning Entity Framework 6 ------ Introduction to TPH

Sometimes, you have created two models. They have the same parent class like this:

public class Person
{
    public int PersonId { get; set; }

    public string PersonName { get; set; }
}

public class InsidePerson : Person
{
    public string Title { get; set; }

    public string Department { get; set; }
}

public class OutsidePerson : Person
{
    public string CompanyName { get; set; }
}

After you execute the command Update-Database in nuget command line, Entity Framework will create one table named people:

The Discriminator column is created for discriminating what model dose current row represent. this model creating type is called TPH(Table per Hierarchy Inheritance). Let's do a test. Add some codes in main function:

static void Main(string[] args)
{
    using (MyDbContext db = new MyDbContext())
    {
        Person insidePerson1 = new InsidePerson()
        {
            PersonName = "InsidePerson1",
            Title = "Manager",
            Department = "development"
        };
        db.People.Add(insidePerson1);

        InsidePerson insidePerson2 = new InsidePerson()
        {
            PersonName = "InsidePerson2",
            Title = "Manager",
            Department = "development"
        };
        db.People.Add(insidePerson2);

        InsidePerson insidePerson3 = new InsidePerson()
        {
            PersonName = "InsidePerson3",
            Title = "Manager",
            Department = "development"
        };
        db.InsidePeople.Add(insidePerson3);

        Person outsidePerson1 = new OutsidePerson()
        {
            PersonName = "outsidePerson1",
            CompanyName = "Tencent"
        };
        db.People.Add(outsidePerson1);

        db.SaveChanges();
    }
}

Let's look at the database:

Lerning Entity Framework 6 ------ Introduction to TPH

If you don't like the discriminator column which entity framework auto create, you can define your column by adding these codes in OnModelCreating function of DbContext class:

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
    base.OnModelCreating(modelBuilder);

    modelBuilder.Entity<Person>()
        .Map<InsidePerson>(p => p.Requires("PersonType").HasValue(1))
        .Map<OutsidePerson>(p => p.Requires("PersonType").HasValue(2));
}

Then, execute the command Add-Migration AddPesonTypeColumn2PeopleTable and Update-Database in nuget command line. Now, look at the database again:

Lerning Entity Framework 6 ------ Introduction to TPH

We can find the Entity Framework can't insert any value into PersonType column of existed rows. It's a little sad. Now, We insert some new data by coding:

static void Main(string[] args)
{
    using (MyDbContext db = new MyDbContext())
    {
        Person insidePerson4 = new InsidePerson()
        {
            PersonName = "InsidePerson4",
            Title = "Manager",
            Department = "development"
        };
        db.People.Add(insidePerson4);

        Person outsidePerson2 = new OutsidePerson()
        {
            PersonName = "outsidePerson2",
            CompanyName = "Baidu"
        };
        db.People.Add(outsidePerson2);

        db.SaveChanges();
    }
}

Look at the databas again:

Lerning Entity Framework 6 ------ Introduction to TPH

That's all.