Entity Framework avoid LazyLoading / already open DataReader issue

Question

With an Union Query which runs several times successively I get UserlistSection objects for each alphabetic letter, if Users exist with the starting letter. So I get something like this:

• UserlistSection "A"
  • User
  • User
• UserlistSection "H"
  • User
• UserlistSection "Y"
  • User
  • User
  • User

But the query throws following exception

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

The query Task

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;
            }
        });
    }

And my Object / Method to create the Collection

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;
    }

There are probably better ways to build the query, but I couldn't figure out how yet. So would be nice if someone can see my mistakes to avoid the LazyLoading / solve the exception.

If I'm missing some explanation, please just tell.

Edit

When I add MultipleActiveResultSets=True like that, it tells me that the keyword isn't support?

<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)

Answer 1

You should enable MARS in your connectionstring in config.

Add "MultipleActiveResultSets=True" to connection string.

More info .

EDIT

From MSDN :

When you call the Load method during a foreach (C#) or For Each (Visual Basic) enumeration, the Entity Framework tries to open a new data reader. This operation will fail unless you have enabled multiple active results sets by specifying multipleactiveresultsets=true in the connection string. For more information, see Using Multiple Active Result Sets (MARS) on MSDN. You can also load the result of the query into a List collection, which closes the data reader and enables you to enumerate over the collection to load referenced entities

EDIT

For MySQL i found this . Mayby it helps you.

It seems that MySQL does not support MARS. If you can change the database for MS SQL Server Express. Or change the ORM for example NHibernate.