Hi,

In our current use-case I am trying to create a more complex MJoined table.

The structure is pretty much straight forward to the documentation, sample code is posted below.

Actually what I am trying to achieve is, to get a select/dropdown for TableD.ColD (foreign keys saved in TableC).
And a second select/dropdown for TableF.ColE - depending on the chosen value fir TableD.ColD.

Using a simple LeftJoin, and one MJoin works like a charm.

Adding the second MJoin causes it to break, using the TryCatch i was able to get a little more detailed error message:
"Object reference not set to an instance of an object."
(maybe because TableD.ID which is needed for the Join only exists in another block?)

Also I noticed that MJoining a table from another database does not work (TableD and TableF are supposed to be in another database than TableA and TableB moving them to the same database is currently a workaround, at least for development).
I tried this (DatabaseName.TableName, and DatabaseName.SchemaName.TableName): https://datatables.net/forums/discussion/21012/editor-1-3-1-connect-to-multiple-databases

Here's some code:

Controller:

 public ActionResult MyEditor()
        {
            var settings = Properties.Settings.Default;
            var formData = HttpContext.Request.Form;

            using (var db = new Database(settings.DbType, ConnectionString)
            {
                   var response = new Editor(db, "TableA", "TableA.ID")
            .TryCatch(false)
                        .Model<TableABModel>()
                        .Field(new Field("TableA.ID").Set(false))
                        .Field(new Field("TableB.ID").Set(false))
                        .LeftJoin("TableB", "TableB.ID", "=", "TableA.B_FK")
                        .MJoin(
                            new MJoin("TableD")
                            .Model<TableDModel>()
                            .Link("TableA.ID", "TableC.A_FK")
                            .Link("TableD.ID", "TableC.D_FK")
                            .Field(new Field("ID")
                                .Options("TableD", "ID", "ColD")
                            )                                        
                        )
                        .MJoin(
                            new MJoin("TableF")
                            .Model<TableEModel>()
                .Link("TableD.ID", "TableE.D.FK")
                            .Link("TableF.ID", "TableE.F_FK")
                            .Field(new Field("ID")
                                .Options("TableF", "ID", "ColE")
                            )
                        )
                   .Process(formData)
                   .Data();

                    JavaScriptSerializer js = new JavaScriptSerializer();
                    js.MaxJsonLength = Int32.MaxValue;
                    ContentResult result = new ContentResult
                    {
                        Content = js.Serialize(response),
                        ContentType = "application/json"
                    };
                    return result;
            }
        }

TableABModel:

public class TableABModel : DataTables.EditorModel
    {
 
        public class TableA
        {
            public int ID { get; set; }
            public string B_FK { get; set; }
            public string ColA{ get; set; }
            public string ColB{ get; set; }
        }
        public class TableB
        {
            public int ID { get; set; }
            public string ColC{ get; set; }
        }
}

TableDModel:

public class TableDModel : DataTables.EditorModel
   {
       public int ID { get; set; }
       public string ColD{ get; set; }
   }

TableFModel:

public class TableFModel : DataTables.EditorModel
   {
       public int ID { get; set; }
       public string ColE{ get; set; }
   }

Shouldn't be that big of a deal I guess.

Cheers,
Eisenkiefer