the differences of DataRelation class between 1.1 and 2.0

when u use the follow code on 1.1.it will compile without error. 

        /**//// <summary>
        /// Test table relation.
        /// </summary>
        public void Relation_1_1()
        ...{
            DataTable dtParent = this.CreateDataTable();
            dtParent.TableName = "Parent";

            DataRelation relations = ds.Relations.Add("Relation", dtParent.Columns["index"], dtParent.Columns["parent_index"], false);

            this.builder.Append(" Get the data from tree ROOT.");
            this.GetLayerFromParent(ds, relations);
            this.PrintDataTable(ds.Tables["parent"]);

            this.builder.Append(" Get the data from tree CHILDS.");
            this.GetLayerFromChilds(ds, relations);
            this.PrintDataTable(ds.Tables["parent"]);

            this.DebugPrint(this.builder.ToString());
        }

while it will run error on 2.0 with "Cannot create a DataRelation if Parent or Child Columns are not in a DataSet.".

if u want to run normally,u can use this cod:

/**//// <summary>
        /// Test table relation.
        /// </summary>
        public void Relation_2_0()
        ...{
            DataTable dtParent = this.CreateDataTable();
            dtParent.TableName = "Parent";

            DataSet ds = new DataSet();
            ds.Tables.Add(dtParent);
            DataRelation relations = ds.Relations.Add("Relation", ds.Tables["Parent"].Columns["index"], ds.Tables["Parent"].Columns["parent_index"], false);

            this.builder.Append(" Get the data from tree ROOT.");
            this.GetLayerFromParent(ds, relations);
            this.PrintDataTable(ds.Tables["parent"]);

            this.builder.Append(" Get the data from tree CHILDS.");
            this.GetLayerFromChilds(ds, relations);
            this.PrintDataTable(ds.Tables["parent"]);

            this.DebugPrint(this.builder.ToString());
            
            //this.WriteToTxtFile(this.builder.ToString());
        }

what's your idea?