How to only select specific properties from an object graph in Entity Framework?

Question

I have a simple data model

car
 - make
 - model
 - year
 - colour
 - engine
     - model
     - no. cylinders
     - size
     - etc
 - fuel tank
     - mode         


        

Answer 1

You only need to use Include if you want to pull the full entities back - you don't need these to do a projection. You can do a projection either anonymously, or using a defined model class. The following code should get you started:

// Define model...
public class CarModel
{
    public string Make { get; set; }
    public string Model { get; set; }
    public int EngineCC { get; set; }
}

// Project to list of models
var cars = context.Cars.Select(c => new CarModel
{
    Make = c.Make,
    Model = c.Model,
    EngineCC = c.Engine.CC
}).ToList();

You can make this much simpler by using a mapping library such as AutoMapper. Using AutoMapper, this becomes:

// (at start of project)
Mapper.Initialize(c => {
    c.CreateMap<Car, CarModel>();
});

// Projection...
var cars = context.Cars.ProjectTo<CarModel>().ToList();

In this example, EngineCC was automatically mapped from Engine.CC, but you can manually specify any mappings which don't just work automatically. AutoMapper will create a Linq projection, only bringing back the properties you need.