Faking enums in Entity Framework 4.0

Question

There are a lot of workarounds for the missing support of enumerations in the Entity Framework 4.0. From all of them I like this one at most:

http://blogs.msdn.com/b/alexj/archive/2009/06/05/tip-23-how-to-fake-enums-in-ef-4.aspx?PageIndex=2#comments

This workaround allows you to use enums in your LINQ queries which is what i exactly need. However, I have a problem with this workaround. I get for every complex type I'm using a new partial autogenerated class.Therefore the code does not compile any more because I already have a wrapper class with this name in the same namespace which converts betwen the backed integer in the database and the enum in my POCO classes. If I make my wrapper a partial class, the code still does not compile as it now contains two properties with the same name "Value". The only possibility is to remove the Value property by hand everytime I generate the POCO classes because the DB model changed (which during the development phase happens very often).

Do you know how to prevent a partial class to be generated out of complex property everytime the EF model changes?

Can you recommend me some other workarounds supporting enumerations in LINQ queries?

Answer 1

That workaround is based on the fact that you are writing your POCO classes yourselves = no autogeneration. If you want to use it with autogeneration you must heavily modify T4 template itself.

Other workaround is wrapping enum conversion to custom extension methods.

public static IQueryable<MyEntity> FilterByMyEnum(this IQueryable<MyEntity> query, MyEnum enumValue)
{
    int val = (int)enumValue;
    return query.Where(e => e.MyEnumValue == val);
}

You will then call just:

var data = context.MyEntitites.FilterByMyEnum(MyEnum.SomeValue).ToList();

Answer 2

I am using an approach based on the one described in your link without any modifications of the T4 templates. The contents of my partial wrapper classes are as follows:

public partial class PriorityWrapper
{
    public Priority EnumValue
    {
        get
        {
            return (Priority)Value;
        }
        set
        {
            Value = (int)value;
        }
    }

    public static implicit operator PriorityWrapper(Priority value)
    {
        return new PriorityWrapper { EnumValue = value };
    }

    public static implicit operator Priority(PriorityWrapper value)
    {
        if (value == null)
            return Priority.High;
        else
            return value.EnumValue;
    }
}

I've only changed that instead of a back store variable with enum value I am using the autogenerated int typed Value property. Consequently Value can be an auto-implemented property and EnumValue property needs to do the conversion in getter and setter methods.