Ad-hoc type with property that looks like collection navigation does not fail model validation

[ajcvickers]

Instead, it is just ignored. Reference navigations will cause validation to fail.

Code:

public class Blog
{
    public string? Name { get; set; }
    public virtual List<Post> Posts { get; } = new();
}

public class Post
{
    public string? Title { get; set; }
}

public class SomeDbContext : DbContext
{
    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        => optionsBuilder
            .UseSqlServer(@"Data Source=(LocalDb)\MSSQLLocalDB;Database=AllTogetherNow")
            .LogTo(Console.WriteLine, LogLevel.Information)
            .EnableSensitiveDataLogging();

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder.Entity<Blog>().HasNoKey();
        modelBuilder.Entity<Post>().HasNoKey();
    }
}

public class Program
{
    public static async Task Main()
    {
        using (var context = new SomeDbContext())
        {
             await context.Database.EnsureDeletedAsync();
             await context.Database.EnsureCreatedAsync();

             await context.SaveChangesAsync();
        }
    }
}

Model:

Model: 
  EntityType: Blog Keyless
    Properties: 
      Name (string)
  EntityType: Post Keyless
    Properties: 
      Title (string)

[ajcvickers]

This is apparently by design:

• efcore/test/EFCore.Tests/ModelBuilding/OneToManyTestBase.cs

  Line 931 in adf3a13

  public virtual void Keyless_type_with_unmapped_collection_navigations_does_not_throw()

• Add more tests for keyless entity types #23195

We should decide if this is also okay for ad-hoc types, which are always keyless.

[ajcvickers]

Note from triage: leave behavior unchanged for normal keyless types, but throw in validation for ad-hoc types.