How to handle error “method 'First' can only be used as a final query operation”

Question

I want to retrieve data from the database in different tables by relation, but I get an error that I don\'t know how to handle.

int customer_id = int.Parse(this.         


        

Answer 1

The error is stating that you should use FirstOrDefault() instead of First()

Not sure what the question is

int customer_id = int.Parse(this.comboBoxnamecustomer.SelectedValue.ToString());

a = (from c in db.Invoices where c.CustomerID == customer_id select new { 
         customerName=c.Customer.Name,ProductName=c.InvoiceItems.Where(x=> x.InvoiceId==c.InvoiceId).FirstOrDefault().Product.ProductsName.Name
        }).ToList();
        dataGridViekryar.DataSource = a;

Of course this will throw an error if there isn't any items from your query (NullReferenceException)