EF Code First Error - entity-framework

Question

I am trying to create some tables using Code First. Here is my code:
public class Country
{
[Key]
public int Id { get; set; }
public string CountryName { get; set; }
}
public class State
{
[Key]
public int Id { get; set; }
public string StateName { get; set; }
public int CountryId { get; set; }
public Country Country { get; set; }
}
public class Customer
{
[Key]
public int Id { get; set; }
public string Name { get; set; }
public int CountryId { get; set; }
public int StateId { get; set; }
public virtual Country Country { get; set; }
public virtual State State { get; set; }
}
public class ProductContext : DbContext
{
public DbSet<Country> Country { get; set; }
public DbSet<Customer> Customer { get; set; }
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
modelBuilder.Conventions.Remove<PluralizingTableNameConvention>();
}
}
When I Execute this code the following error occurs:
Introducing FOREIGN KEY constraint
'FK_dbo.State_dbo.Country_CountryId' on table 'State' may cause cycles
or multiple cascade paths. Specify ON DELETE NO ACTION or ON UPDATE NO
ACTION, or modify other FOREIGN KEY constraints. Could not create
constraint. See previous errors.
But I want the CountryId in State Table to be a foreign key. What am I missing here? Can anybody guide me the correct way of achieving this?

Answer 1

Entity Framework is worried about deletion here- because the User has a direct relationship to a Country and also a State and the State also relates to a Country you effectively have a potential loop of User -> State -> Country -> User which would mean that if cascade deletions were enabled the moment you deleted one user you would potentially delete everything in your database.
The answer is in the error message- by disabling cascade deletions across some of these relationships ( which is logical - deleting a user doesn't mean you want to delete their state and country ) you will avoid this risk. As you might imagine this has come up on SO before.
As an aside, having the Country on the User and also on the State looks like questionable denormalisation - there may be a good reason for it, but that happens less often than you would expect.