实体框架基于跨多个子集合的过滤器的选择对象

Question

Assume I have the following domain (not my actual domain, but a trivial example)

public class ClassRoom
{
  public int Id {get;set;}
  public string Name {get;set;}
  public virtual ICollection<Desk> Desks{get;set;}
  public virtual ICollection<LunchBox> LunchBoxs{get;set;}
}

public class Desk
{
  public int Id {get;set;}
  public String Colour {get;set;}
  public String Make {get;set;}
  Public ClassRoom ClassRoom {get;set;}
}

public class LunchBox
{
  public int Id {get;set;}
  public String Colour {get;set;}
  public int Volume {get;set;}
}

I would like to be able to query as follows

"Give me all the classes that have blue desks or green lunchboxes" returning a list of classes

I would have thought the code to be

var efClasses = (from d in myentity.ClassRooms
                  where ( (d.Desks.Colour == "blue")
                         || (d.LunchBoxs.Colour == "green) )
select d).Distinct();

doing this gives me the error

Cannot convert lambda expression to type 'string' because it is not a delegate type (obviously unhappy about the Colour, it expects a method here

so I changed it to this as an experiment

var efClasses = (from d in myentity.ClassRoom
                  where ( (d.Desks.Where(x=>x.Colour == "blue"))
                         || (d.LunchBoxs.Where(x=>x.Colour == "green)) )
select d).Distinct();

But this wont compile either (In hindsight I had a feeling I was trying my luck on this.

I could go the other way around by changing my from to be myentity.Desks, and myEntity.Lunchboxs, and return two seperate lists of ClassRooms, and then find the union, but this will require 2 separate DB hits, and feels hacky

Answer 1

Instead of using count > 0, you can use Any

var efClasses = (from d in myentity.ClassRoom
                 where (d.Desks.Any(x => x.Colour == "blue") ||
                        d.LunchBoxs.Any(x => x.Colour == "green"))
                 select d);

Answer 2

Use Count >0 like this.

 var efClasses = (from d in myentity.ClassRoom
                             where (d.Desks.Count(x => x.Colour == "blue") > 0
                                    || d.LunchBoxs.Count(x => x.Colour == "green") > 0)
                             select d);