Use enum as FK in EF6

Question

We have a enum Supplier

But now we need to also have some Domain data on that relation

So in 99.9% in the domain code we doe operations on the enum like product.Supplier == Suppliers.FedEx

But now we also have added product.SupplierInfo.CanAdjustPickupTime where SupplierInfo is a Entity and not just a simple enum type.

I have tried these configs

Property(p => p.Supplier)
    .IsRequired()
    .HasColumnName("SupplierId");

HasRequired(p => p.SupplierInfo)
    .WithMany()
    .HasForeignKey(p => p.Supplier); //I have also tried casting to int doing .HasForeignKey(p => (int)p.Supplier)

This will fail with

The ResultType of the specified expression is not compatible with the required type. The expression ResultType is 'MyApp.Model.Suppliers' but the required type is 'Edm.Int32'. Parameter name: keyValues[0]

Also tried

Property(l => l.Supplier)
    .IsRequired()
    .HasColumnName("SupplierId");

HasRequired(p => p.SupplierInfo)
    .WithMany()
    .Map(m => m.MapKey("SupplierId"));

This will offcourse give the good old

One or more validation errors were detected during model generation:

SupplierId: Name: Each property name in a type must be unique. Property name 'SupplierId' is already defined.

I could offcourse define SupplierId as a Property use that with HasForeignKey But then I need to change to .SuppliedId == (int)Suppliers.FedEx etc. Not really a solution.

I could also add a property enum that uses the SupplierId property as backing field, but this will not work with Expressions since it needs to use real mapped DB properties

Any ideas?

Answer 1

I have classes:

public class Agreement
{
    public int Id { get; set; }
    public AgreementStateTypeEnum AgreementStateId { get; set; }
}

public class AgreementState
{
    public int Id { get; set; }
    public string Title { get; set; }
}

context:

 public class AgreementContext :DbContext
 {
     public AgreementContext() : base("SqlConnection") { }
     public DbSet<Agreement> Agreements { get; set; }
 }

In method OnModelCreating I wrote nothing. My enum:

 public enum AgreementStateTypeEnum : int
 {
        InReviewing = 1,
        Confirmed = 2,
        Rejected = 3 
 }

In database: in table Agreements I have foreign key AgreementStateId - it is link to table AgreementStates . Everything is working. For example:

var temp = context.Agreements.First(x => x.AgreementStateId == AgreementStateTypeEnum.Confirmed);

I use enum how foreign key.

Answer 2

Finally I found the problem. (I'm using EF6, NET 4.5) So, if you create a type Enum in your code, you couldn't create a relationship with other property virtual.

//This is wrong, when do you create a foreignkey using a type  enum
//Do You should remove that's code on in your class Map.
 HasRequired(p => p.SupplierInfo)
.WithMany()
.HasForeignKey(p => p.Supplier); //I have also tried casting to int doing 
.HasForeignKey(p => (int)p.Supplier)

If did you created a type enum it means that you don't need for a table return data throught for a join in EF. So, the correct code it is:

public class MyClass{

public enum myEnumType {
FedEx,
Olther
} 

public int id {get;set;}
public myEnumType Supplier {get;set;}

}

//My class Map (using Fluent...)    
public class MyClassMap {

HasKey(t => t.Id);
Property(t => t.Id).HasColumnName("Id");
//The type [supplier] should be [int] in database.
Property(t => t.Supplier).HasColumnName("supplier");
//That's all, you don't need write relationship, int this case 
//Because, when the data returns, the EF will to do the conversion for you.

}

I hope that's useful

Answer 3

The best way I have found to deal with this scenario is to map Supplier as a regular domain object and create a separate class of known supplier IDs.

public class KnownSupplierIds
{
    public const int FedEx = 1;
    public const int UPS = 2;
    // etc.
}

if (product.Supplier.SupplierId == KnownSupplierIds.Fedex) { ... };

When your code needs to check the supplier, it can compare the IDs; when you need additional info from the domain model you just load the Supplier. The reason I prefer using a class of constants instead of an enum is that the pattern works for string comparisons also and there's no need to cast.