How to use an existing enum with Entity Framework DB First

Question

I am using Entity Framework 5, DB first. I know how to define an enum on my model, and set the type of a field to that enum.

Now, I have a requirement to map a field MyField to an enum that is defined externally, ie not in the EF model ( OtherNamespace.MyEnum ). The designer does not allow me to set the type to anything outside the model. I tried editing the edmx file manually, but that causes an error:

Error 10016: Error resolving item 'MyField'. The exception message is: 'Unresolved reference 'OtherNamespace.MyEnum'.'.

OtherNamespace.MyEnum is referenced by my project.

How do you do it?

Answer 1

This can be done, but it requires a little sacrifice on the database side. Entity Framework (5 onwards) supports mapping a field to an enumeration, but only for byte , sbyte , short , ushort , int , uint , long , or ulong types.

Assume that we have the following sample table:

CREATE TABLE [People](
    [id] [int] IDENTITY(1,1) NOT NULL PRIMARY KEY,
    [Name] [varchar](50) NOT NULL,
    [Title] [int] NOT NULL
)

Title has been declared as an integer. In a real database, this might be a foreign key over to a TitleTypes table.

Also, let's assume that the external enumeration that we are going to be tying into is defined as:

namespace Enumerations
{
    public enum TitleEnum
    {
        Mr,
        Mrs,
        Dr,
        None
    }
}

If we import the People table into an EDMX we can right click on the Title column and Convert to Enum

This will bring up a dialog box allowing us to specify a name for the enumeration in the EDMX ModelStore, define any values for the enumeration OR link to an external enumeration via Reference external type .

Give it a Type Name of TitleEnum , check Reference external type , and type Enumerations.TitleEnum in the provided field. Click OK and it will associate the column to the external enumeration.

Note:

• While both are called TitleEnum, this is acting as a passthrough to the external Enumeration
• The type of your column and the external enumeration MUST match

Now, when we create a new person we can utilize the enumeration and it will be translated into its Int representation.

Data.ScratchEntities context = new Data.ScratchEntities();
Data.Person person = new Data.Person();
person.Name = "Jane Smith";
//Note the use of the external enumeration here
person.Title = Enumerations.TitleEnum.Mrs;
context.People.Add(person);
context.SaveChanges();