Can I store enums as strings in EF 5?

问题:

We have been using EF CF for a while in our solution. Big fans! Up to this point, we've been using a hack to support enums (creating an extra field on the model; ignore the enum durring mapping; and map the extra field to the column in the db that we would have used). Traditionally we have been storing our enums as strings(varchars) in the DB (makes it nice and readable). Now with enum support in EF 5 (Beta 2) it looks like it only supports mapping enums to int columns in the DB....Can we get EF 5 to store our enums as their string representation.

Where "Type" is an enum of type DocumentType

public enum DocumentType 
    {
        POInvoice,
        NonPOInvoice,
        Any
    }

I tried to map it using:

public class WorkflowMap : EntityTypeConfiguration<Model.Workflow.Workflow>
    {
        public WorkflowMap()
        {
            ToTable("Workflow", "Workflow");
            ...
            Property(wf => wf.Type).HasColumnType("varchar"); 

        }
    }

I thought was going to be the magic bullet but..

That just throws:

Schema specified is not valid. Errors: (571,12) : error 2019: Member Mapping specified is not valid. The type 'Dodson.Data.DataAccess.EFRepositories.DocumentType[Nullable=False,DefaultValue=]' of member 'Type' in type 'Dodson.Data.DataAccess.EFRepositories.Workflow' is not compatible with 'SqlServer.varchar[Nullable=False,DefaultValue=,MaxLength=8000,Unicode=False,FixedLength=False]' of member 'Type' in type 'CodeFirstDatabaseSchema.Workflow'.

Your thoughts?

回答1:

This is currently not possible. Enum in EF has same limitations as enums in CLR - they are just named set of integer values. Check this article for confirmation:

The EF enum type definitions live in conceptual layer. Similarly to CLR enums the EF enums have underlying type which is one of Edm.SByte, Edm.Byte, Edm.Int16, Edm.Int32 or Edm.Int64 with Edm.Int32 being the default underlying type if none has been specified.

I posted article and related suggestion about this problem. If you want to see this feature in the future please vote for the suggestion.

回答2:

I hit this problem a few weeks ago. The best I could come up with is a bit hacky.

I have a Gender enum on the class Person, and I use data annotations to map the string to the database and ignore the enum.

public class Person
{
    public int PersonID { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }

    [Column("Gender")]
    public string GenderString
    {
        get { return Gender.ToString(); }
        private set { Gender = value.ParseEnum<Gender>(); }
    }

    [NotMapped]
    public Gender Gender { get; set; }
}

And the extension method to get the correct enum from the string.

public static class StringExtensions
{
    public static T ParseEnum<T>(this string value)
    {
        return (T)Enum.Parse(typeof(T), value, true);
    }
}

See this post for full details - http://nodogmablog.bryanhogan.net/2014/11/saving-enums-as-strings-with-entity-framework/