EF6嵌套列表的單個LINQ查詢

Question

我只想使用EntityFramework使用單個LINQ查詢來填充數據庫實體中的嵌套列表。

我有3個表實體。 一流的Cities包含List<Houses>而Houses包含List<Residents> 。

這些類：

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;} 
}

我想要實現的是這樣的：

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()

不幸的是，我遇到錯誤The entity or complex type Houses cannot be constructed in a LINQ to Entities 。

它僅對Houses = db.Houses.Where(h=>h.CityId ==city.CityId).ToList() 。 但是，這使我失去了Houses Residents 。

甚至可以用一個LINQ查詢嗎？

Answer 1

您只需要在城市查詢中包括房屋和居民：

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

Answer 2

您應該使用導航屬性，而不是單獨的db訪問

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()

沒有檢查整個語法，只更換db.Houses.Where(...)由city.Houses （有相同的Residents ），所以可能有一些其他問題。