Schema specified is not valid. Errors: The relationship was not loaded because the type is not available

I wish to reference the OrderAddress model twice in my Order model; once as a ShippingAddress and once as a BillingAdress.

On the other side, I want my OrderAddress model to have a list of OrderAddresses.

OrderAddress Model

public enum AddressType
{
    Billing,
    Shipping,
    Contact
}
public class OrderAddress : BaseModel
{
    public AddressType AddressType { get; set; }
    public bool IsPrimary { get; set; }

    public string Address { get; set; }
    public string CityStateZip { get; set; }
    public string ContactName { get; set; }
    public string PhoneNumber { get; set; }
    public string FaxNumber { get; set; }
    public string EmailAddress { get; set; }

    public virtual ICollection<Order> Orders { get; set; }

    public virtual ApplicationUser User { get; set; }
}

Order Model

public class Order : BaseModel
{
    public DateTime OrderDate { get; set; }

    public int BillingAddressId { get; set; }
    public virtual OrderAddress BillingAddress { get; set; }

    public int ShippingAddressId { get; set; }
    public virtual OrderAddress ShippingAddress { get; set; }

    public virtual ApplicationUser User { get; set; }

}

Fluent API

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

    modelBuilder.Entity<Order>()
                .HasRequired(m => m.ShippingAddress)
                .WithMany(t => t.Orders)
                .HasForeignKey(m => m.ShippingAddressId)
                .WillCascadeOnDelete(false);

    modelBuilder.Entity<Order>()
                .HasRequired(m => m.BillingAddress)
                .WithMany(t => t.Orders)
                .HasForeignKey(m => m.BillingAddressId)
                .WillCascadeOnDelete(false);
}

When I try to run Update-Database, I get the following error:

Schema specified is not valid. Errors: The relationship 'MyApp.Domain.DAL.Order_ShippingAddress' was not loaded because the type 'MyApp.Domain.DAL.OrderAddress' is not available.

What am I doing wrong?

The error is a little cryptic, so I'm not sure if this is the reason you're getting that particular error, but I do know it will cause some error, so you can start by fixing this:

What you have is two one-to-many relationships to the same model on one class. That's not a problem per se, but you have to treat them as separate. In other words, they can't both have a opposite relationship of Orders, because relationally, there's no way to know which foreign key relationship should populate that list. If you simply change your fluent API definition to something like .WithMany(t => t.Orders_Shipping) and .WithMany(t => t.Orders_Billing), I think that will clear up your error.

Stacked

You need to change your OrderAddress entity and your Fluent API mappings to the following:

OrderAddress:

public class OrderAddress : BaseModel
{
    ...
    public virtual ICollection<Order> BillingOrders { get; set; }
    public virtual ICollection<Order> ShippingOrders { get; set; }
    ...
}

Fluent API:

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

    modelBuilder.Entity<Order>()
                .HasRequired(m => m.ShippingAddress)
                .WithMany(t => t.ShippingOrders)
                .HasForeignKey(m => m.ShippingAddressId)
                .WillCascadeOnDelete(false);

    modelBuilder.Entity<Order>()
                .HasRequired(m => m.BillingAddress)
                .WithMany(t => t.BillingOrders)
                .HasForeignKey(m => m.BillingAddressId)
                .WillCascadeOnDelete(false);
}

Check this SO post for more, it is about the same problem as yours.

Had this issue. I believe it is something to do with the web service. My solution was after updating the service reference and the config operation took place. the problem went away. hope this helps.

In my case I had this error because I made another partial class with the same name as the class generated by entity framework. Except mine did not matche the case. For example:

public partial class Vehicle
{
    public string Name { get; set; }
    public string Make { get; set; }
    ...
}

public partial class VEhicle
{
    public override bool Equals(object obj)
    {
       ...
    }
}

I got the same error using database first: "The relationship was not loaded because the type ... is not available". The problem was the model in the solution was outdated. To fix the problem: