EF6: materializing data using custom type - entity-framework

Question

Assuming I have an entity:
public class Event
{
...
public DateTime At { get; set; }
}
As well as a model object:
public class Something
{
...
public Date At { get; set; }
}
where Date is a custom type which can be implicitly converted from a DateTime:
public struct Date
{
public Date(DateTime value)
{
...
}
...
public static implicit operator Date(DateTime value)
{
return new Date(value);
}
}
What I'm trying to do is to fetch the data from database into the model:
var events = db.Events
.Select(x => new Something
{
...
At = x.At,
})
.ToList();
And of course this is failing with the following exception:
Unable to cast the type 'System.DateTime' to type 'SMG.Web.Date'. LINQ to Entities only supports casting EDM primitive or enumeration types.
Yes, I know that I could achieve what I need with the help of some temporary object, materialize DateTime value into memory and then convert it into my custom type. But what if I prefer not to use this strategy, and want to do this in one step.
The question is: Is there a way to teach LINQ to Entities how to treat my custom Date on that side of reality?

Answer 1

Your cast is the wrong way around. Rewrite it as:
public struct Date
{
public Date(DateTime value)
{
DateTimeValue = value;
}
// Or whatever your field or property is called
public DateTime DateTimeValue { get; }
public static implicit operator DateTime(Date date)
{
return date.DateTimeValue;
}
}
Then EF should let you use it in expressions. This approach will not work for code-first EF.