協會性質不裝載在實體

Question

我有三個相關實體，由該圖最好地描述：

alt text http://thehashtable.com/wp-content/uploads/2010/01/Enttities.png

當我加載用戶，使用下面的代碼，所述User對象被加載，即不爲空，但User對象上的Role和Department屬性爲空，儘管用戶數據庫記錄具有這些關聯的有效FK值。

using (var productionEntities = new ProductionEntities()) 
{ 
    var userName = GetUserName(); 
    User u = (from usr in productionEntities.UserSet 
       where usr.UserName == userName 
       select usr).FirstOrDefault(); 
    if (u == null) 
    { 
     throw new KpiSecurityException("No local database entry found for user.") { UserName = userName }; 
    } 
    return u.Department.DeptName; 
} 

題外話：我通過這整個任務就只是因爲ASP.NET的MembershipProvider不支持用戶的元數據「像部，我將不得不使用ProfileProvider爲好，成本巨大的數據庫膨脹。

Answer 1

既然你只需要該部門的名稱，只是project了這一點;這樣你只能查詢一次數據庫：

using (var productionEntities = new ProductionEntities()) 
{ 
    var userName = GetUserName(); 
    var u = (from usr in productionEntities.UserSet 
       where usr.UserName == userName 
       select new 
       { 
        DeptName = usr.Department.DeptName 
       }).FirstOrDefault(); 
    if (u == null) 
    { 
     throw new KpiSecurityException("No local database entry found for user.") { UserName = userName }; 
    } 
    return u.DeptName; 
} 

Answer 2

你必須明確你的查詢加載此特性

User u = (from usr in productionEntities.UserSet 
      where usr.UserName == userName 
      select usr).FirstOrDefault(); 

if (u == null) 
{ 
     throw new KpiSecurityException("No local database entry found for user.") { UserName = userName }; 
} 

if (!u.RoleReference.IsLoaded) 
{ u.RoleReference.Load(); } 

if (!u.DeparmentReference.IsLoaded) 
{ u.DeparmentReference.Load(); } 

或包含此實體

User u = (from usr in productionEntities.UserSet.Include("Role").Include("Department") 
      where usr.UserName == userName 
      select usr).FirstOrDefault();