DataRelation manipulation in Asp.net

Question

Hi All,

I am trying to establish the relationship between two tables but its showing the following error

Object reference not set to an instance of an object.

 the code is as followsDataRelation oDR = new DataRelation("Dept_Emp", oDS.Tables["tbl_Department"].Columns["DNo"], oDS.Tables["tbl_EmpDept"].Columns["DNo"], false);