Updating counter in XQuery

Question

I want to create a counter in xquery. My initial attempt looked like the following:

let $count := 0
for $prod in $         


        

Answer 1

As @Ranon said, all XQuery values are immutable, so you can't update a variable. But if you you really need an updateable number (shouldn't be too often), you can use recursion:

declare function local:loop($seq, $count) {
  if(empty($seq)) then ()
  else
    let $prod  := $seq[1],
        $count := $count + 1
    return (
      { $count },
      local:loop($seq[position() > 1], $count)
    )
};

local:loop($collection, 0)

This behaves exactly as you intended with your example.

In XQuery 3.0 a more general version of this function is even defined in the standard library: fn:fold-right($f, $zero, $seq)

That said, in your example you should definitely use at $count as shown by @tohuwawohu.