嵌套列表的 EF6 单个 LINQ 查询

Question

我只想使用单个 LINQ 查询来填充 Entity（使用 EntityFramework） 中的嵌套列表。

我有 3 个表实体。头等Cities包含List<Houses>，Houses包含List<Residents>。

这些类：

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;} 
}

我想要实现的是这样的：

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，我收到错误The entity or complex type Houses cannot be constructed in a LINQ to Entities.

它有效，仅适用于Houses = db.Houses.Where(h=>h.CityId ==city.CityId).ToList().但这样一来，我在Houses中失去了Residents.

甚至可以用一个 LINQ 查询来做吗？

Answer 1

您只需要将房屋和居民包含在城市查询中：

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

Answer 2

应使用导航属性，而不是单独的db访问

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()

没有检查整个语法，只用city.Houses替换了db.Houses.Where(...)（与Residents相同），因此可能存在其他一些问题。