Linq 'into' keyword confusion

Question

I was looking at a co-workers Linq query, shown below (the query executes correctly):

from ea in EquipmentApplication
join erl in EquipmentRoutingLocation on         


        

Answer 1

To add to what has already been said, I'd like to demonstrate the difference in the object structure produced by into versus without:

var q = 
    from c in categories 
    join p in products on c equals p.Category into ps 
    select new { Category = c, Products = ps }; 

Creates an object graph:

Category 1, Products:
  Product 1
  Product 2
Category 2, Products:
  Product 3
  Product 4

In this case, q only contains 2 items, the two categories.

Without into, you get a more traditional join that flattens the relationship by creating all possible combinations:

var q = 
    from c in categories 
    join p in products on c equals p.Category 
    select new { Category = c, Product = p }; 

Category 1, Product 1
Category 1, Product 2
Category 2, Product 3
Category 2, Product 4

Note that now q contains 4 items.

Update, I think:

var q = 
    from c in categories 
    join p in products on c equals p.Category into ps 
    select new { Category = c, Products = ps.Select(x=> x.Id) };