Question

我有三个相关实体，最好用这个图描述：

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

当我加载用户时，使用以下代码加载User对象，即不为空，但Role和Department对象上的User和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; }属性尽管用户数据库记录具有这些关联的有效FK值，但仍为null。

{{1}}

ASIDE：我完成了整个任务，因为ASP.NET MembershipProvider不支持像部门一样的用户“元数据”，我也不得不使用ProfileProvider，巨大的数据库膨胀成本。

Answer 1

您必须明确加载此属性

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(); }

或在查询中包含此实体

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

Answer 2

由于您只需要部门名称，只需要project;这样你只需要查询一次数据库：

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;
}

关联属性未加载到实体上

2 个答案: