Problems setting up EF5 and a Lookup Table

Question

I'm trying to design a code-first model with a TPH Lookup Table like the following:

public abstract class LookupValue
{
   [Key]
   public string Value { get; set; }
}

public class PaymentTerm : LookupValue {}
public class ShippingCode : LookupValue {}
public class ReviewStatus : LookupValue {}
public class RecordStatus : LookupValue {}

I want Entity Framework to generate a table with a discriminator, which it does, as follows;

CREATE TABLE [LookupValues] (
    [Value] [nvarchar](30) NOT NULL,
    [Discriminator] [nvarchar](128) NOT NULL,
    CONSTRAINT [PK_dbo.LookupValues] PRIMARY KEY ([Value])
)

In my context OnModelCreating override, I defined the following:

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
    modelBuilder.Entity<PaymentTerm>()
                .Map(m => m.Requires("Discriminator").HasValue("PaymentTerm"));
    modelBuilder.Entity<ShippingCode>()
                .Map(m => m.Requires("Discriminator").HasValue("ShippingCode"));
    modelBuilder.Entity<ReviewStatus>()
                .Map(m => m.Requires("Discriminator").HasValue("ReviewStatus"));
    modelBuilder.Entity<RecordStatus>()
                .Map(m => m.Requires("Discriminator").HasValue("RecordStatus"));
}

I want to use these lookup objects as follows:

public class Customer {
     ....
     [Required]
     public virtual PaymentTerm Terms { get; set; }

     [Required]
     public virtaul ShippingCode ShippingCode { get; set; }

     [Required]
     public virtual ReviewStatus ReviewStatus { get; set; }

     [Required]
     public virtual RecordStatus RecordStatus { get; set; }
     ...
}

I can create the Code-First Migration, but when I attempt to Update The Database, I get an error

The referential relationship will result in a cyclical reference that is not allowed...

I've figured out that this is due to the ON DELETE CASCADE that the SQL Script generates as follows:

ALTER TABLE [Customer] ADD CONSTRAINT [FK_dbo.Customer_dbo.LookupValues_ShippingCode_Value] FOREIGN KEY ([ShippingCode_Value]) REFERENCES [LookupValues] ([Value]) ON DELETE CASCADE
ALTER TABLE [Customer] ADD CONSTRAINT [FK_dbo.Customer_dbo.LookupValues_PaymentTerms_Value] FOREIGN KEY ([PaymentTerms_Value]) REFERENCES [LookupValues] ([Value]) ON DELETE CASCADE
ALTER TABLE [CustomerClinicDoctors] ADD CONSTRAINT [FK_dbo.Customer_dbo.LookupValues_RecordStatus_Value] FOREIGN KEY ([RecordStatus_Value]) REFERENCES [LookupValues] ([Value]) ON DELETE CASCADE
ALTER TABLE [Customer] ADD CONSTRAINT [FK_dbo.Customer_dbo.LookupValues_ReviewStatus_Value] FOREIGN KEY ([ReviewStatus_Value]) REFERENCES [LookupValues] ([Value]) ON DELETE CASCADE

I've read that I should put the .WillCascadeOnDelete(false) in the fluent api, but I can't get it to accept it. Hoping for some help...

How can I turn off the DELETE CASCADE on these relationships. I don't intend do really need the ability to delete the lookup values, but just wanted a simple code interface in my Repository.

Answer 1

You need to define fluent mapping for every relation. Try this:

public class YourContext : DbContext {
    protected override void OnModelCreating(DbModelBuilder modelBuilder) {
        modelBuilder.Entity<Customer>()
                    .HasRequired(c => c.Terms)
                    .WithMany()
                    .WillCascadeOnDelete(false);

        modelBuilder.Entity<Customer>()
                    .HasRequired(c => c.ShippingCode)
                    .WithMany()
                    .WillCascadeOnDelete(false);

        modelBuilder.Entity<Customer>()
                    .HasRequired(c => c.ReviewStatus)
                    .WithMany()
                    .WillCascadeOnDelete(false);

        modelBuilder.Entity<Customer>()
                    .HasRequired(c => c.RecordStatus)
                    .WithMany()
                    .WillCascadeOnDelete(false);
    }
}