Question

I just asked this question. Which lead me to a new question 🙂

Up until this point, I have used the following pattern of selecting stuff with Linq to SQL, with the purpose of being able to handle 0 ‘rows’ returned by the query:

var person = (from p in [DataContextObject].Persons               where p.PersonsID == 1               select new p).FirstOrDefault();  if (person == null) {     // handle 0 'rows' returned. } 

But I can’t use FirstOrDefault() when I do:

var person = from p in [DataContextObject].Persons              where p.PersonsID == 1              select new { p.PersonsID, p.PersonsAdress, p.PersonsZipcode };  // Under the hood, this pattern generates a query which selects specific // columns which will be faster than selecting all columns as the above // snippet of code does. This results in a performance-boost on large tables. 

How do I check for 0 ‘rows’ returned by the query, using the second pattern?

UPDATE:

I think my build fails because I am trying to assign the result of the query to a variable (this._user) declared with the type of [DataContext].User.

this._user = (from u in [DataContextObject].Users               where u.UsersID == [Int32]               select new { u.UsersID }).FirstOrDefault(); 

Compilation error: Cannot implicitly convert type ‘AnonymousType#1’ to ‘[DataContext].User’.

Any thoughts on how I can get around this? Would I have to make my own object?

Answer 1

Regarding your UPDATE: you have to either create your own type, change this._user to be int, or select the whole object, not only specific columns.