Question

I am using EF CF approach for a website with MySQL.
For some reason EF creates a column in my Post table called “Discriminator” and contains the VARCHAR “Post”.

Why is this column created? Can I do something to avoid it being created? Are there any advantages of having this column?

Answer 1

The Discriminator column is used and required in Table-Per-Hierarchy inheritance scenarios. If you for example have a model like this …

public abstract class BaseEntity
{
    public int Id { get; set; }
    //...
}

public class Post : BaseEntity
{
    //...
}

public class OtherEntity : BaseEntity
{
    //...
}

… and make the BaseEntity part of the model, for instance by adding a DbSet<BaseEntity> to your derived context, Entity Framework will map this class hierarchy by default into a single table, but introduce a special column – the Discriminator – to distinguish between the different types (Post or OtherEntity) stored in this table. This column gets populated with the name of the type (again Post or OtherEntity).