The Fluent API HasDiscriminator Method

The Entity Framework Core Fluent API HasDiscriminator method is used to configure aspects of the discriminator column in a table that represents an inheritance hierarchy.

By convention, a discriminator column will be configured to use a string data type will be named "Discriminator". The HasDiscriminator method takes a type parameter reprsenting the data type for the column, and a string representing the name for the column. In the following example, the table used to store instances of entities that inherit from the abstract Contract entity will feature a discriminator column named "ContractType":

public class SampleContext : DbContext
{
    public DbSet<MobileContract> MobileContracts { get; set; }
    public DbSet<BroadbandContract> BroadbandContracts { get; set; }

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder.Entity<Contract>()
            .HasDiscriminator<string>("ContractType");
    }
}

public abstract class Contract
{
    public int ContractId { get; set; }
    public DateTime StartDate { get; set; }
    public int Months { get; set;}
    public decimal Charge { get; set; }
}

public class MobileContract : Contract
{
    public string MobileNumber { get; set; }
}

public class BroadbandContract : Contract
{
    public int DownloadSpeed { get; set; }
}

By default, EF Core will use the type name as a discriminator value. If you want to use another data type, such as an integer, you must also use the HasValue method to provide values for all concrete type in the inheritance hierarchy. The following example configures the discriminator column's data type as numeric and provides default values for each type:

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    modelBuilder.Entity<Contract>()
        .HasDiscriminator<int>("ContractType")
        .HasValue<MobileContract>(1)
        .HasValue<BroadbandContract>(2);
}

Data Annotations

No Data Annotations are available for configuring discriminator columns.

Further Reading


Created:
Last updated: 14/03/2017 16:33:44
Proficiency Level: Beginner