EF 返回的 FK collection 为空，但验证重复项，确认 collection 有内容

Question

我正在尝试获取所有用户无人机的数据，但 ef core 返回空 collection。

public class User : AuditableEntity
   {
       public Guid Id { get; set; }
       public string Name { get; set; }
       public string Email { get; set; }
       public string UserData { get; set; }
       public bool IsActive { get; set; }
       public bool IsAdmin { get; set; }
       public DateTime LastActivity { get; set; }
       public IEnumerable<Drone> Drones { get; set; }
   }
public class Drone : AuditableEntity
   {
       public Guid Id { get; set; }
       public string CustomName { get; set; }
       public string Model { get; set; }
       public int Serial { get; set; }       
       public bool IsActive { get; set; }
       public string DroneData { get; set; }
       public virtual User User { get; set; }
   }

和user.Drones总是有空值，我无法获取和显示数据，但是这行验证代码

if (user.Drones.Contains(drone))
                    return ("This drone has been alredy registred", false);

告诉我，user.Drones 包含值。为什么我应该这样做，得到 user.Drones collection?

Answer 1

Ef 使用延迟加载，加载子实例必须使用 Include

var user = context.Users.Where (i=> i.Id==userId)
.Include(i=>i.Drones)
.FirstOrDefault();

//or if you want just drones

var userDrones=context.Users.Where (i=> i.Id==userId)
.Select(i=>i.Drones)
.FirstOrDefault();

但最好给Drone显式添加一个外键UserId

public class Drone : AuditableEntity
   {
       public Guid Id { get; set; }
       .....

      public Guid UserId { get; set; }
       public virtual User User { get; set; }
   }

并使用此查询

var userDrones=context.Drones.Where (i=> i.UserId==userId).ToList();

EF 返回的 FK collection 为空，但验证重复项，确认 collection 有内容

FK collection returned by EF is null, but validation for duplicates, confirms thats, the collection has content

c#

asp.net

entity-framework-core

.net-core