C# linq 如何编写子查询?

C# linq 如何编写子查询?

string[] ids = (from DeductionBill in t_ds_DeductionBill where t_ds_DeductionBill .BillNumber.Equals(c.BillNumber)) .ToArray();

TotalWeight= (from Order in t_kd_Order where(item => ids.Contains(item.OrderID))
select Order.TotalWeight ).Sum();

public List GetList(string name, string product)
{
var table = from c in _db.BBCustomer
where (!string.IsNullOrEmpty(name) ? c.Name.Contains(name) : true) &&
(!string.IsNullOrEmpty(product) ? c.ProductName.Contains(product) : true)
orderby c.CID descending
select c;
return table.ToList();
}