how to fix this error

Question

I am new to entity frame work 

when  trying to insert data to  Database 

 

 

iam gettin  error "'System.Data.Objects.ObjectSet<Entityframeworkinsertupdelete.Departement>' does not contain a definition for 'Add' and no extension method 'Add' accepting a first argument of type 'System.Data.Objects.ObjectSet<Entityframeworkinsertupdelete.Departement>' could be found (are you missing a using directive or an assembly reference?)" 

 

protected void Button1_Click(object sender, EventArgs e)

{

welcometestingEntities context = new welcometestingEntities();

department obj = new department();

obj._name = TextBox1.Text;

obj._location = TextBox2.Text;

 

context.Departements.Add(obj); //error on this line

//--- Bind data to repeater.

bindStudentInfo();

//--- Show confirmation message in label.

//--- Clear text from textboxes

}

 

please help me

 

thanks