c# - Entity Framework 4.3 - TPH mapping and migration error

Question

I'm using Entity Framework 4.3 with code first and manual migrations. I'm trying to map a TPH (table-per-hierarchy) setup which uses two custom discriminator fields. One for the discriminator itself and the other for soft deletes (much like the "where" option in NH class mappings). The exact same setup works just fine in another project which runs on EF 4.2.

I get the error when trying to add a migration using the "add-migration" command in the NuGet console. I have tried all combinations of defining the table name - attributes on class, in "OnModelCreating" method, in EntityTypeConfiguration classes etc. My previous migrations which didn't involve complex hierarchy mappings have worked just fine.

Is there some breaking change in EF 4.3 that I've stumbled upon?

The code:

//---- Domain classes ---------------------

public abstract class ParentClass
{
    public string ParentString { get; set; }
}

public class Foo : ParentClass
{
    public string FooString { get; set; }
}

public class Bar : ParentClass
{
    public string BarString { get; set; }
}

//---- Mapping configuration --------------

public class ParentConfiguration : EntityTypeConfiguration<ParentClass>
{
    public ParentConfiguration()
    {
        Map<Foo>(m =>
        {
            m.Requires("IsActive").HasValue(1);
            m.Requires("Type").HasValue("Foo");
        })
        .ToTable("Parent");

        Map<Bar>(m =>
        {
            m.Requires("IsActive").HasValue(1);
            m.Requires("Type").HasValue("Bar");
        })
        .ToTable("Parent");
    }
}

//---- Context ----------------------------

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
    modelBuilder.Configurations.Add(new ParentConfiguration());
}

The error:

System.InvalidOperationException: The type 'Foo' has already been mapped to table 'Parent'. Specify all mapping aspects of a table in a single Map call.
   at System.Data.Entity.ModelConfiguration.Configuration.Types.EntityTypeConfiguration.AddMappingConfiguration(EntityMappingConfiguration mappingConfiguration)
   at System.Data.Entity.ModelConfiguration.Configuration.ModelConfiguration.ReassignSubtypeMappings()
   at System.Data.Entity.DbModelBuilder.Build(DbProviderManifest providerManifest, DbProviderInfo providerInfo)
   at System.Data.Entity.DbModelBuilder.Build(DbConnection providerConnection)
   at System.Data.Entity.Infrastructure.EdmxWriter.WriteEdmx(DbContext context, XmlWriter writer)
   at System.Data.Entity.Migrations.Extensions.DbContextExtensions.<>c__DisplayClass1.<GetModel>b__0(XmlWriter w)
   at System.Data.Entity.Migrations.Extensions.DbContextExtensions.GetModel(Action`1 writeXml)
   at System.Data.Entity.Migrations.Extensions.DbContextExtensions.GetModel(DbContext context)
   at System.Data.Entity.Migrations.DbMigrator..ctor(DbMigrationsConfiguration configuration, DbContext usersContext)
   at System.Data.Entity.Migrations.DbMigrator..ctor(DbMigrationsConfiguration configuration)
   at System.Data.Entity.Migrations.Design.ToolingFacade.BaseRunner.GetMigrator()
   at System.Data.Entity.Migrations.Design.ToolingFacade.GetPendingMigrationsRunner.RunCore()
   at System.Data.Entity.Migrations.Design.ToolingFacade.BaseRunner.Run()

Mihkel

Answer 1

This is a known issue with 4.3 and 4.3.1. (We found it too late to put the fix in 4.3.1.) Luckily there is a fairly simple way to change your code that should make it work.

In a nutshell, you used to be able to make chained map calls on a single EntityConfiguration in 4.1. and 4.2. Something like this pattern:

modelBuilder.Entity<Parent>()
    .Map<Foo>(...)
    .Map<Bar>(...);

This doesn't work in 4.3 and instead you have to make each Map call on an EntityConfiguration for that entity. So a pattern something like this:

modelBuilder.Entity<Foo>()
   .Map<Foo>(...);

modelBuilder.Entity<Bar>()
   .Map<Bar>(...);

Taking your case specifically, this should work:

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
    modelBuilder.Entity<ParentClass>()
        .ToTable("Parent");

    modelBuilder.Entity<Foo>()
        .Map(m =>
                {
                    m.Requires("IsActive").HasValue(1);
                    m.Requires("Type").HasValue("Foo");
                });

    modelBuilder.Entity<Bar>()
        .Map(m =>
                {
                    m.Requires("IsActive").HasValue(1);
                    m.Requires("Type").HasValue("Bar");
                });
}

(I've removed a few of the generic parameters since they aren't needed, but that's not important.)

Doing this using explicit EntityConfigurations you would use something like this:

public class ParentConfiguration : EntityTypeConfiguration<ParentClass>
{
    public ParentConfiguration()
    {
        ToTable("Parent");
    }
}

public class FooConfiguration : EntityTypeConfiguration<Foo>
{
    public FooConfiguration()
    {
        Map(m =>
        {
            m.Requires("IsActive").HasValue(1);
            m.Requires("Type").HasValue("Foo");
        });
    }
}

public class BarConfiguration : EntityTypeConfiguration<Bar>
{
    public BarConfiguration()
    {
        Map(m =>
        {
            m.Requires("IsActive").HasValue(1);
            m.Requires("Type").HasValue("Bar");
        });
    }
}

And then

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
    modelBuilder.Configurations
        .Add(new ParentConfiguration())
        .Add(new FooConfiguration())
        .Add(new BarConfiguration());
}

We plan to fix this in 5.0.