Use projection to fill not mapped types in EF

Question

We have a specific struct called Measure and we'd like to use this type instead of the database field type eg double.

So we have an entity:

public class MyEnity
{
   public int MyValue { get; set; }
}

And we have a transfer object: public class MyDto { public Measure MyMeasureValue{ get; set; } }

If the property type would match, we just can fill our dto's per projection:

enities.Select(i => new MyDto { MyMeasureValue = new Measure(i.MyValue, _unitsService.GetUnit("km")) });

But since EF does not support such statements, we have to refill this, or load the whole entity:

entities.Select(i => new { MyValue = i.MyValue })
        .AsEnumerable()
        .Select(i => new MyDto { MyMeasureValue = new Measure(i.MyValue, _unitsService.GetUnit("km")) } );

We want to avoid this looping several times in the refill process, especially because there are a lot of properties to fill. Is there a way we can go with the first statement and teach EF to execute the Measure creation? (eg interception etc.)

PS. It is not an option to create a EF complex type and map it!

Thanks Enyra

Answer 1

You may use complex types while fetching some properties of the entity using Linq-Entity. For instance;

Model1Container container = new Model1Container();
var temp = from o in container.MasterSet
           select new
                  {
                       x = o.LastModifiedBy,
                       y = o.LastModifiedDate
                  };

By the way, instead of mapping DTOS by hand, it is better to use autommaper. It has the functionality to map matching proper names without explicity declaring.