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xdmp:set

xdmp:set(
   $variable as item()*,
   $expr as item()*
) as empty-sequence()

Summary

Set the value of a variable to the specified expression. The xdmp:set command allows you to introduce changes to the state (side effects) of a query by changing the value of a variable to something other than what it is bound to.

Parameters
$variable A variable to set.
$expr A value to set the variable.

Usage Notes

When a variable is bound to a sequence in a for loop, and when that variable is changed by xdmp:set in the return clause, the change only affects the value for one iteration of the for loop at a time; when the next value is sent to the return clause, it is set to the next value in the sequence specified in the for clause. The value changes only after the xdmp:set call is made.

Example

(: set the value of the variable $x
   to 1234 and then print out $x :)

let $x := 12
return
(xdmp:set($x, 1234), $x)

=> 1234

Example

(: set the value of the variable $x
   to 5 and then print out $x for
   each value of $y :)

for $x in (1, 2)
  for $y in ($x, $x)
return
($y, xdmp:set($x, 5), $x)

=> (1, 5, 1, 5, 2, 5, 2, 5)

Example

(: note the effect on $z of changing the
   value of $x :)

for $x in (1, 2)
  for $y in (3,4)
    for $z in ($x, $x)
return
($z, xdmp:set($x, 5))

=> (1, 1, 5, 5, 2, 2, 5, 5)

Example

(: every time the name of the input node changes,
   output the new name  :)

let $n := ()
for $i in (<x>1</x>, <x>2</x>, <y>3</y>)
return (
   if (name($i) eq $n)
   then ()
   else (xdmp:set($n, name($i)), $n)
  , data($i)
)

=> (x, 1, 2, y, 3)

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