实体框架避免延迟加载/已打开的数据读取器问题

使用连续运行多次的联合查询，如果起始字母存在Users，我会为每个字母UserlistSection对象。所以我得到这样的东西：

• 用户列表部分"A"
  • 用户
  • 用户
• 用户列表部分"H"
  • 用户
• 用户列表部分"Y"
  • 用户
  • 用户
  • 用户

但查询引发以下异常

MySql.Data.MySqlClient.MySqlException: There is already an open DataReader associated with this Connection which must be closed first.

查询任务

public UserRepository(myDatabase database)
    {
        _database = database;
    }
public Task<ObservableCollection<User>> GetUserFriendsAsync(int id, string letter)
    {
        return Task.Factory.StartNew(() =>
        {
            try
            {
                var query1 = (from urs in _database.user_relationships
                              join u in _database.users on urs.relationship_user_from equals u.user_id
                              where urs.relationship_user_to == id
                                    && u.user_name.StartsWith(letter)
                                    && urs.relationship_status == 1
                              select new User
                              {
                                  Id = u.user_id,
                                  Username = u.user_name,
                                  AvatarByte = u.user_avatar,
                                  Gender = u.user_gender,
                                  GroupId = u.user_usergroup,
                                  LoginStatusId = u.user_loginstatus
                              });
                var query2 = (from urs in _database.user_relationships
                              join u in _database.users on urs.relationship_user_to equals u.user_id
                              where urs.relationship_user_from == id
                                    && u.user_name.StartsWith(letter)
                                    && urs.relationship_status == 1
                              select new User
                              {
                                  Id = u.user_id,
                                  Username = u.user_name,
                                  AvatarByte = u.user_avatar,
                                  Gender = u.user_gender,
                                  GroupId = u.user_usergroup,
                                  LoginStatusId = u.user_loginstatus
                              });
                // Union to get users via relationships (from - to and to - from)
                var queryUnion = query1.Union(query2).OrderBy(u => u.Username);
                return new ObservableCollection<User>(queryUnion);
            }
            catch (Exception ex)
            {
                Trace.WriteLine("UserRepository - GetUserFriendsAsync" + ex);
                return null;
            }
        });
    }

和我的对象/方法来创建集合

public class UserlistSection : ObservableObject
{
    #region Attributes
    private string _letter;
    private ObservableCollection<User> _users;
    #endregion Attributes
    public string Letter
    {
        get { return _letter; }
        set { Set(ref _letter, value); }
    }
    public ObservableCollection<User> Users
    {
        get { return _users; }
        set { Set(ref _users, value); }
    }
}
// -------------------------------------------------------------------------
 public async void UpdateFriendlistCollection()
    {
        IsLoading = true;
        Friendlist = new ObservableCollection<UserlistSection>();
        for (var c = 'A'; c <= 'Z'; c++)
        {
            try
            {
                var letter = c.ToString();
                var userCollection = await _userRepository.GetUserFriendsAsync(_userObj.Id, letter);
                if (userCollection.Count < 1) return;
                foreach (var friend in userCollection)
                {
                    friend.AvatarImage = friend.GetAvatarImgByPixel(200);
                }
                var section = new UserlistSection
                {
                    Letter = letter,
                    Users = userCollection
                };
                Friendlist.Add(section);
            }
            catch (Exception ex)
            {
                Trace.WriteLine("FriendlistViewModel - UpdateFriendlistCollection: " + ex.Message);
            }
        }
        IsLoading = false;
    }

可能有更好的方法来构建查询，但我还不知道如何。所以如果有人能看到我的错误以避免懒惰加载/解决异常，那就太好了。

如果我缺少一些解释，请告诉。

编辑

当我添加这样的MultipleActiveResultSets=True时，它告诉我不支持关键字？

<connectionStrings>
<add name="someDatabase"   connectionString="metadata=res://*/Repository.Database.SomeDatabase.csdl|res://*/Repository.Database.SomeDatabase.ssdl|res://*/Repository.Database.SomeDatabase.msl;provider=MySql.Data.MySqlClient;provider connection string=&quot;server=127.0.0.1;user id=someUser;persistsecurityinfo=True;password=somePassword;multipleactiveresultsets=True;database=someDatabase;&quot;" providerName="System.Data.EntityClient" />

System.ArgumentException: Keyword not supported.
Parametername: multipleactiveresultsets
bei MySql.Data.MySqlClient.MySqlConnectionStringBuilder.GetOption(String key)
bei MySql.Data.MySqlClient.MySqlConnectionStringBuilder.set_Item(String  keyword, Object value)