The Fluent API HasValue Method

The Entity Framework Core Fluent API HasValue method is used to configure discriminator values for entities in an inheritance hierarchy when a table per hierarchy approach is chosen for mapping inheritance to a database.

The HasValue method is available on the DiscriminatorBuilder type, which is returned when the HasDiscriminator method is called. It takes a type parameter specifying the type that the value applies to, and an object representing the value to apply to the specified type. In the following example, the discriminator values for the MobileContract type and the BroadbandContract type are configured as 1 and 2 respectively.

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

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

Data Annotations

It is not possible to configure discriminator values with Data Annotation attributes.

Further Reading


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