Question

I have a query below. although can anyone point out what “from p” means? and also “var r”?

DataClasses1DataContext db = new DataClasses1DataContext(); 
            var r = from p in db.Products 
                    where p.UnitPrice > 15 // If unit price is greater than 15...
                    select p; // select entries

Answer 1

r is the composed query – an IQueryable<Product> or similar; note the query has not yet executed – it is just a pending query. var means “compiler, figure out the type of r from the expression on the right”. You could have stated it explicitly in this case, but not all. But it wouldn’t add any value, so var is fine.

p is a convenience marker for each product; the query is “for each product (p), restricting to those with unit price greater than 15 (where p > 15), select that product (select p) as a result.

Ultimately this compiles as:

IQueryable<Product> r =
    db.Products.Where(p => p.UnitPrice > 15);

(in this case, a final .Select(p => p) is omitted by the compiler, but with a non-trivial projection, or a trivial query, the .Select(...) is retained)