c# DataRelations 问题

未将对象引用设置到对象的实例
vs.net2003
SqlDataAdapter thisAdapter = new SqlDataAdapter("select * from customers", conn);
SqlCommandBuilder thisBuilder = new SqlCommandBuilder(thisAdapter);
DataSet ds = new DataSet();

SqlDataAdapter cusAdapter = new SqlDataAdapter("select * from customers", conn);
SqlDataAdapter orderAdapter = new SqlDataAdapter("select * from orders", conn);
cusAdapter.Fill(ds, "customers");
orderAdapter.Fill(ds, "customers");
//DataRelation custOrderRel = ds.Relations.Add("CustOrders",
DataRelation custOrderRel = new DataRelation("CustOrders",
ds.Tables["customers"].Columns["customerId"],
ds.Tables["orders"].Columns["customerId"]);
ds.Relations.Add(custOrderRel);

foreach(DataRow custRow in ds.Tables["customers"].Rows)
{
Console.WriteLine("CustomerId:&q

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