Enum type mapping discriminator support

Npgsqls Enum Type Mapping is very nice. Unfortunately its not possible to use enums in the discriminator configuration.

For example the following code …

class SampleContext : DbContext
{
	public SampleContext(DbContextOptions options)
		: base(options)
	{ }

	static SampleContext()
		=> NpgsqlConnection.GlobalTypeMapper.MapEnum<PersonType>();

	public DbSet<Person> Persons { get; set; }

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

		modelBuilder.HasPostgresEnum<PersonType>();

		modelBuilder.Entity<Person>()
		.HasDiscriminator()
		.HasValue<FactoryWorker>(PersonType.FactoryWorker)
		.HasValue<Manager>(PersonType.Manager);

		modelBuilder.Entity<Manager>();
		modelBuilder.Entity<FactoryWorker>();
	}
}

public abstract class Person
{
	public int Id { get; set; }
	public string Value { get; set; }
	public Instant Timestamp { get; set; }
}

public class Manager : Person
{
	public string Position { get; set; }
}

public class FactoryWorker : Person
{
	public string FactoryName { get; set; }
}

public enum PersonType
{
	Manager,
	FactoryWorker
}

… yields the following exception:

Cannot set discriminator value ‘FactoryWorker’ for discriminator property ‘Discriminator’ because it is not assignable to property of type ‘System.String’.

It would be nice to use enums for discriminator columns.

[roji]

Great! Good to know it worked out. Enums really are a sort of natural fit as discriminators, just keep in mind the limitations of altering them (https://github.com/npgsql/efcore.pg/issues/1308#issuecomment-599136265).

[davidroth]

Thanks @roji for your help! Very much appreciated!

Adding a static constructor fixed it. This way the global type mapping gets also updated during design-time db context creation.

static BlogContext()
{
    NpgsqlConnection.GlobalTypeMapper.MapEnum<PersonType>();
    NpgsqlConnection.GlobalTypeMapper.MapEnum<UserType>();
}