Mix of owned and normal entity types in hierarchy should cause validation error

[SharpSeeEr]

Observed Behavior

Using the following setup with an Address class that is used as an Owned Entity and as a base class for the ContactAddress class:

public class OwnedTypesContext : DbContext
{
    public DbSet<House> Houses { get; set; }
    public DbSet<Contact> Contacts { get; set; }

    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    {
        optionsBuilder.UseSqlServer(@"Server=(localdb)\mssqllocaldb;Database=OwnedTypesInheritence;Trusted_Connection=True;");
        base.OnConfiguring(optionsBuilder);
    }
    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder.Entity<House>()
            .OwnsOne(e => e.Address);
        
        base.OnModelCreating(modelBuilder);
    }
}

public class Address
{
    [MaxLength(500)] public string StreetAddress1 { get; set; }
    [MaxLength(200)] public string City { get; set; }
    [MaxLength(2)]   public string State { get; set; }
    [MaxLength(5)]   public string Zip { get; set; }
}

public class ContactAddress : Address
{
    public int Id { get; set; }
    public int ContactId { get; set; }
    public Contact Contact { get; set; }
}

public class Contact
{
    public int Id { get; set; }
    [MaxLength(100)] public string FirstName { get; set; }
    [MaxLength(200)] public string LastName { get; set; }
    public List<ContactAddress> Addresses { get; set; } = new List<ContactAddress>();
}

public class House
{
    public int Id { get; set; }
    public Address Address { get; set; }
    public string OwnerName { get; set; }
}

Creating the initial migration works as expected - the ContactAddress table does not have a Discriminator column but the ContextModelSnapshot does show Discriminator column:

modelBuilder.Entity("EFCoreOwnedTypeInheritence.ContactAddress", b =>
    {
        b.Property<int>("Id")
            .ValueGeneratedOnAdd();

        b.Property<string>("City")
            .HasMaxLength(200);

        b.Property<int>("ContactId");

        b.Property<string>("Discriminator") // <---  Exists in Model Snapshot
            .IsRequired();

        b.Property<string>("Label")
            .HasMaxLength(25);

        b.Property<string>("State")
            .HasMaxLength(2);

        b.Property<string>("StreetAddress1")
            .HasMaxLength(500);

        b.Property<string>("Zip")
            .HasMaxLength(5);

        b.HasKey("Id");

        b.HasIndex("ContactId");

        b.ToTable("ContactAddress");

        b.HasDiscriminator<string>("Discriminator").HasValue("ContactAddress");
    });

All subsequent migrations, even if no changes were made, result in the following:

protected override void Up(MigrationBuilder migrationBuilder)
{
    migrationBuilder.DropColumn(
        name: "Discriminator",
        table: "ContactAddress");
}

protected override void Down(MigrationBuilder migrationBuilder)
{
    migrationBuilder.AddColumn<string>(
        name: "Discriminator",
        table: "ContactAddress",
        nullable: false,
        defaultValue: "");
}

If you run dotnet ef database update it gives the error:

ALTER TABLE DROP COLUMN failed because column 'Discriminator' does not exist in table 'ContactAddress'

Expected Behavior

The ContextModelSnapshot would not have any reference to a Discriminator column for an Owned Type, and migrations would not continuously DropColumn(name: "Discriminator") and AddColumn(name: "Discriminator")

Steps to reproduce

1. Clone Test Case Project
2. Run the following commands:

dotnet restore
dotnet ef migrations add Initial
dotnet database update
dotnet ef migrations add Second
dotnet database update

1. View the .\Migrations*_Second.cs migration file.

Further technical details

EF Core version: 2.0.0
Database Provider: Microsoft.EntityFrameworkCore.SqlServer 2.0.0
Operating system: Microsoft Windows 10 Pro Version 1709 OS Build 16299.19
IDE: Visual Studio 2017 15.4.1, VS Code 1.17.2

[ajcvickers]

Related to #9630 and discussion in #9536

[ajcvickers]

@SharpSeeEr To be honest, we didn't consider the case of having a base type which is an owned entity and then another mapping for the derived type that is not an owned entity. Right now this should be considered not supported--we will use this bug to track adding better validation for this when building a model. Beyond this, issue #9630 is tracking support for inheritance in owned type, which will ultimately decide whether or not this mix of owned/normal entities in a hierarchy will be supported.