Linq connection request error

Question

I am trying to join multiple datasets to create a single datatable type. Here is the request.

var row = from r0w1 in dt_vi.AsEnumerable()
          join r0w2 in dt_workcenter.AsEnumerable()
          on r0w1.Field<int>("wcID") equals r0w2.Field<int>("iD")
          join r0w3 in dt_recipe.AsEnumerable()
          on r0w1.Field<int?>("curingRecipeID") equals r0w3.Field<int?>("recipe_id") join r0w4 in dt_defect.AsEnumerable()
          on r0w1.Field<int?>("defectID") equals r0w4.Field<int?>("defect_id") into ps
          from r0w4 in ps.DefaultIfEmpty()
          select r0w1.ItemArray.Concat(r0w2.ItemArray.Concat(r0w3.ItemArray.Concat(r0w4.ItemArray))).ToArray();

foreach (object[] values in row)
    dt.Rows.Add(values);

I tried to join r0w1 and r0w4 as LEFT OUTER JOIN. But here I get an error

Object reference not set to object instance

The error seems to be in

r0w4.ItemArray

Maybe r0w4 does not get any value. What could be the possible reason?

Answer 1

The task ps.DefaultIfEmpty()will return the default value ( nullin this case) if no row matches and thus throws this error.

You can change it like this: -

r0w3.ItemArray.Concat(r0w4 != null ? r0w4 .ItemArray : new object[] {}))