Using a partial class property inside LINQ statement

Question

I am trying to figure out the best way to do what I thought would be easy. I have a database model called Line that represents a line in an invoice.

It looks roughly

Answer 1

There is another way, which is a bit more complex, but gives you the ability to encapsulate this logic.

public partial class Line
{
    public static Expression> TotalExpression
    {
        get
        {
            return l => l.Price * l.Quantity
        }
    }
}

Then rewrite the query to

var invoices = ( from c in _repository.Customers
                     where c.Id == id
                     from i in c.Invoices
                     select new InvoiceIndex
                     {
                         Id = i.Id,
                         CustomerName = i.Customer.Name,
                         Attention = i.Attention,
                         Total = i.Lines.AsQueryable().Sum(Line.TotalExpression),
                         Posted = i.Created,
                         Salesman = i.Salesman.Name
                     }
               )

It worked for me, performs queries server-side and complies with the DRY rule.