error on _ds.Relations.Add

Question

User222331888 posted

Hi,

I don't know why I've an error on this :

            _ds.Relations.Add("Polls_Answers",
                  _ds.Tables["Polls"].Columns["PollID"],
                  _ds.Tables["PollAnswers"].Columns["PollID"]);

My error is :  

 {"Object reference not set to an instance of an object."}

 

            conn.Open();

            string strSql = "SELECT GroupID, GroupName FROM [Group]; " +
              "SELECT PollID, DisplayText, Type, GroupID, FolderID " +
              "FROM Polls, TypeAns where Polls.TypeAnsID = TypeAns.TypeAnsID; " +
              "SELECT PollID, PollAnswerID, DisplayText, SortOrder FROM" +
              " PollAnswers";


            SqlDataAdapter da = new SqlDataAdapter(strSql, conn);
            da.TableMappings.Add("Group1", "Polls");
            da.TableMappings.Add("Group2", "PollAnswers");

            DataSet _ds = new DataSet("Polls");
 
            da.Fill(_ds, "Polls");

            _ds.Relations.Add("Polls_Answers",
                  _ds.Tables["Polls"].Columns["PollID"],
                  _ds.Tables["PollAnswers"].Columns["PollID"]);
            _ds.Relations[0].Nested = true;
            _ds.Relations.Add("Polls_Group",
                  _ds.Tables["Polls"].Columns["GroupID"],
                  _ds.Tables["[Group]"].Columns["GroupID"]);
             _ds.Relations[1].Nested = true;

            Repeater1.DataSource = _ds.Tables["Polls"];
            Repeater1.DataBind();

            conn.Close();

 

Thanks a lot for your help,
 

Answer 1

User222331888 posted

Hi,

 

My error come from

            DataColumn table1Column;
            table1Column = _ds.Tables["Polls"].Columns[0];

 My error is still :

System.NullReferenceException was unhandled by user code
  Message="Object reference not set to an instance of an object."
  Source="App_Web_ygpup3yr"
  StackTrace:
       at Quest.Page_Load(Object sender, EventArgs e) in c:\...\Quest.aspx.cs:line 39
       at System.Web.Util.CalliHelper.EventArgFunctionCaller(IntPtr fp, Object o, Object t, EventArgs e)
       at System.Web.Util.CalliEventHandlerDelegateProxy.Callback(Object sender, EventArgs e)
       at System.Web.UI.Control.OnLoad(EventArgs e)
       at System.Web.UI.Control.LoadRecursive()
       at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)
  InnerException:

and my

_ds.Tables["Polls"].Columns[0] '_ds.Tables["Polls"]' is null System.Data.DataColumn

 

So obviously come from my request, where did I messed up? cuz if i apply request by request it works.

Thanks for your help,

 

 

 

Answer 2

User222331888 posted

Hi,

when i feel in my dataset, my tables are there cuz I can see three tables, but then when I check TableNamei've

"Table"

"Table1"

"Table2"

in ((System.Data.DataTable)((new System.Collections.ArrayList.ArrayListDebugView(((System.Data.DataTableCollection)(((System.Data.InternalDataCollectionBase)(_ds.Tables)).SyncRoot)).List)).Items[0])).TableName

 

But in ColumnName, i've the good name of column :

((System.Data.DataColumn)((new System.Collections.ArrayList.ArrayListDebugView(((System.Data.InternalDataCollectionBase)(((System.Data.DataTable)((new System.Collections.ArrayList.ArrayListDebugView(((System.Data.DataTableCollection)(((System.Data.InternalDataCollectionBase)(_ds.Tables)).SyncRoot)).List)).Items[0])).Columns)).List)).Items[1])).ColumnName

GroupId, GroupName....

Any idea?

 

Answer 3

User222331888 posted

            SqlDataAdapter da = new SqlDataAdapter(strSql, conn);
            da.TableMappings.Add("Table", "Group");
            da.TableMappings.Add("Table1", "Polls");
            da.TableMappings.Add("Table2", "PollAnswers");

Sorry my bad that was coming from my missing mapping.

Now it works fine,