Implementing filter using LinqBindingList

JasminK posted on Monday, April 11, 2011

I'm using 3.8.2 version in my web app.

I want to implement filtering on ReadOnlyList object using LinqBindingList.I have CslaDataSource object that is bound to ReadOnlyList object that I want to filter.

protected void CslaDataSource1_SelectObject(object sender, Csla.Web.SelectObjectArgs e)
        {

           e.BusinessObject = GetAllChildObjects();

        }

private MyReadOnlyList GetAllChildObjects()
        {
            object businessObject = Session["currentObject"];
            if(businessObject==null || !(businessObject is MyApp.Library.MyReadOnlyList))
            {
                businessObject = MyReadOnlyList.GetMyReadOnlyList();
                Session["currentObject"] = businessObject;
            }
            return (MyReadOnlyList) businessObject;
        }

Now, I can implement filter using FilteredBinding list but I was looking for more flexible and "cleaner" solution. Could this be implemented using LinqBindingList like this?

private MyReadOnlyList GetFilteredChildObjects()

   {

          object businessObject = Session["currentObject"];
            if(businessObject==null || !(businessObject is MyApp.Library.MyReadOnlyList))

                {

                    LinqBindingList<MyChild> filter = (from x in MyReadOnlyList.GetMyReadOnlyList()

                                                                      where x.MyProperty == someValue

                                                                       select x) as  LinqBindingList<MyChild>;

                    businessObject = filter;

                    Session["currentObject"] = businessObject;

                }

              return (MyReadOnlyList) businessObject;

    }

and after that just to bind CslaDataSource like e.BusinessObject = GetFilteredChildObjects();

I've tried this but I got 'NullReferenceException: Object reference not set to an instance of an object.'

What am I doing wrong?

RockfordLhotka replied on Wednesday, April 13, 2011

It is impossible to say without knowing exactly where that exception originates. The stack trace is required.