efcore-8-owned-relationship: A C# repository from kbaley

Demonstrates an issue (either a bug or with my configuration) with a base class that is used only as an owned relationship but an inherited class is not.

Reported issue: dotnet/efcore#34161

To reproduce

Modify the connection string to match your environment
Run dotnet ef migrations add Moo
Run dotnet ef migrations add Moo2
Run dotnet ef database update

Observed behaviour

The Moo2 migration includes a line to drop a non-existent Discriminator column:

 migrationBuilder.DropColumn(
                name: "Discriminator",
                table: "PersonAddress");

The database update therefore fails as there's no column to drop.

Troubleshooting

Move the AddressId key to the PersonAddress class

Address doesn't need the key and the EF migration doesn't actually create it. But when I try this, I get the following when generating any migration:

Unable to create a 'DbContext' of type ''. The exception 'The entity type 'PersonAddress' requires a primary key to be defined.
If you intended to use a keyless entity type, call 'HasNoKey' in 'OnModelCreating'. For more information on keyless entity types,
see https://go.microsoft.com/fwlink/?linkid=2141943.'

Change Person.Addresses to be an owned relationship

That is, add this to OnModelCreating:

modelBuilder.Entity<Person>()
    .OwnsMany(p => p.Addresses);

This generates a migration that doesn't compile. The model snapshot and migration designer both have this code:

b1.HasDiscriminator().HasValue("PersonAddress");

as part of the OwnsMany for Person and HasDiscriminator doesn't exist in this context.

Explicitly define a table per concrete type strategy

modelBuilder.Entity<PersonAddress>().UseTpcMappingStrategy