access parent field in for expression

[agent-mo]

Hi, I want to use jslt to transform json , but happen an unsolvable problem.

• The input json data like this :
  { "user_id" : "001", "friends": [ { "friend_id": "002" }, { "friend_id": "003" }, { "friend_id": "004" } ] }

• Then , what output json data I expected like the follow :
  [ { "user_id": "001", "friend_id" : "002" }, { "user_id": "001", "friend_id" : "003" }, { "user_id": "001", "friend_id" : "004" } ]

• In jslt expression , I use expression of for to traverse the array field friends :
  [ for (.friends) { "user_id": .user_id , "friend_id" : .friend_id } ]

• However , the treansform result can't get field user_id
  [{"friend_id":"002"},{"friend_id":"003"},{"friend_id":"004"}]

How can I access field user_id out of the scope related array field friends ?
Looking forward for your help， thanks

[larsga]

The thing here is that if we allow accessing the parent it becomes very difficult to reuse nodes from the input in the output, which means we have to do costly copying. There is a simple workaround: you can capture the user id in a variable before you start the loop:

let user_id = (.user_id)
[ for (.friends) { "user_id": $user_id , "friend_id" : .friend_id } ]

[agent-mo]

Nice , thank you ! Your answer fit my requirement .