EF6 Single LINQ Query for nested Lists

Question

I want to use just single LINQ query to fill nested lists in DB Entities using EntityFramework.

I've got 3 Table Entities. First class Cities contains List<Houses> and Houses contains List<Residents> .

Those classes:

class Cities
{
    long CityId {get;set;} 
    string Name {get;set;} 
    List<House> Houses {get;set;} 

}

class Houses 
{
    long CityId {get;set;} 
    string Address {get;set;} 
    List<Resident> Residents {get;set;}

}

class Residents 
{
   long HouseId {get;set;} 
   string FirstName {get;set;} 
   string LastName {get;set;} 
}

What I want to achieve is something like that:

var cities = ( from city in db.Cities
               select new  // Creating anonymous type to fill List of Houses 
               {
                  CityId = city.CityId,
                  Name   = city.Name, 
                  Houses = db.Houses.Where(h=>h.CityId == city.CityId)
                                    .Select( new // Another anonymous type, but this time this isn't working
                                    {
                                        HouseId = h.HouseId,
                                        Address = h.Address,
                                        Residents = db.Residents.Where(r=>r.HouseId == h.HouseId).ToList()
                                    }).ToList()
                                    .Select( h => new Houses
                                    {
                                        HouseId = h.HouseId,
                                        Address = h.Address,
                                        Residents = h.Houses
                                    }).ToList()
               })
               .ToList()
               .Select( c=> new Cities
               {
                  CityId = c.CityId
                  Name   = c.Name, 
                  Houses = c.Houses
               }).ToList()

Unfortunately I am getting error The entity or complex type Houses cannot be constructed in a LINQ to Entities .

It works, just for Houses = db.Houses.Where(h=>h.CityId ==city.CityId).ToList() . But with that I am loosing Residents in Houses .

Is it even possible to do with one LINQ query?

Answer 1

您只需要在城市查询中包括房屋和居民：

var cities = db.Cities.Include(c => c.Houses.Select(h => h.Residents)).ToList();

Answer 2

You should use the navigation properties, not a separate db access

var Cities = (from city in db.Cities
           select new  // Creating anonymous type to fill List of Houses 
           {
              CityId = city.CityId,
              Name   = city.Name, 
              Houses = city.Houses.Select( new
                                {
                                    HouseId = h.HouseId,
                                    Address = h.Address,
                                    Residents = h.Residents.ToList()
                                }).ToList()
                                .Select( h => new Houses
                                {
                                    HouseId = h.HouseId,
                                    Address = h.Address,
                                    Residents = h.Houses
                                }).ToList()
           })
           .ToList()
           .Select( c=> new Cities
           {
              CityId = c.CityId
              Name   = c.Name, 
              Houses = c.Houses
           }).ToList()

Didn't check whole syntax, only replaced db.Houses.Where(...) by city.Houses (same with Residents ), so there might be some other issues.