How to access parent object from nested loop?

[ivanogor]

I have a input json:

{
  "add_params_pdou_import_data": {
    "addParams": [
      {
        "productId": "id1",
        "prodregisters": [
          {
            "accountNumber": "acc1"
          },
          {
            "accountNumber": "acc2"
          }
        ]
      },
      {
        "productId": "id2",
        "prodregisters": [
          {
            "accountNumber": "acc3"
          }
        ]
      }
    ]
  }
}

I have a JSLT function where I'm trying to access a variable defined in the outer loop from inside the nested loop:

let PdouParams = .add_params_pdou_import_data.addParams

def checkPdouAccountNumber(accountNumber)
  [for ($PdouParams) 
    let productId = string(.productId)
    [for (.prodregisters) 
      if ($accountNumber == .accountNumber)
      {
        "id" : $productId,      // ← trying to access outer variable
        "system" : "PDOU"
      }
    ]
  ]

Problem: When I'm inside the inner for (.prodregisters) loop, can I access the $productId variable that was defined in the outer loop?

In result i have syntax problem.

[larsga]

can I access the $productId variable that was defined in the outer loop?

Yes.

In result i have syntax problem.

That might be because this not not a complete JSLT expression. You define a variable and a function, but nothing is actually being evaluated. That's probably what it's complaining about.

[catull]

@ivanogor

Allow me to point out a couple of observations.

1. If you go to JSTL playground and enter your example, you see that your code is syntactically incorrect.
2. For one thing, you have to the encode the assignment of productId as let productId = (.productId). You do not have to stringify it. You can, such as let productId = (string (.productId)). As long as the expression after = is surrounded with parentheses.
3. Prepending the if-statement lets a few nulls slip in; add it to the end, so it acts a a filter. Otherwise you get some [ null] as result.
4. For the nodes in your input with un-matching account numbers, the function produces [ ]. You have to flatten( ...) them.
5. Last point, and this is only required in the playground, you have to call the function checkPdouAccountNumber

So, if you change your code to

let PdouParams = .add_params_pdou_import_data.addParams

def checkPdouAccountNumber(accountNumber)
  flatten([for ($PdouParams)
    let productId = (.productId)
    [for (.prodregisters)
      {
        "id" : $productId,
        "system" : "PDOU"
      } if ($accountNumber == .accountNumber)
    ]
  ])

checkPdouAccountNumber("acc1")

You get:

[ {
  "id" : "id1",
  "system" : "PDOU"
} ]

Good luck!

PS:
@larsga
Point 2) above is not optimal, that you have to enclose an RHS of the assignment in parentheses.
It always trips me up.
Any chance of allowing a short-cut, like let productId = .productId ?

[catull]

@ivanogor

You can break up the task.

transform builds a list of objects containing the attributes accountNumber, id as well as system.
You will need the accountNumber for the next function.
Since you have a for nested in another for, the function results in

[ [ A, B, C ] ]

This is the reason that we have to flatten the result to be

[ A, B, C ]

extractForAccountNumbers processes the transformed input by only taking the objects which have a given account number,

Now you can fetch

extractForAccountNumbers ($transform, ["acc1", "acc3"])

or

extractForAccountNumbers ($transform, ["acc2"])

or

extractForAccountNumbers ($transform, [])  // <- this one will accept any account numbers in the input

Here's the broken up approach:

def transform (params)
  [for ($params)
    let productId = (.productId)
    [for (.prodregisters)giv
      {
        "accountNumber": .accountNumber,
        "id": $productId,
        "system": "PDOU"
      }
    ]
  ]

def extractForAccountNumbers (transform, accountNumbers)
   [ for ($transform)
     {
       "id": .id,
       "system": .system
     } if ([] == $accountNumbers or contains (.accountNumber, $accountNumbers))
   ]

let params    = (.add_params_pdou_import_data.addParams)
let transform = (flatten (transform ($params)))

// various use cases, for illustration
{
  "all"  : extractForAccountNumbers ($transform, []),
  "1"    : extractForAccountNumbers ($transform, ["acc1"]),
  "2and3": extractForAccountNumbers ($transform, ["acc2", "acc3"])
}

The above gives you:

{
    "all": [
        {
            "id": "id1",
            "system": "PDOU"
        },
        {
            "id": "id1",
            "system": "PDOU"
        },
        {
            "id": "id2",
            "system": "PDOU"
        }
    ],
    "1": [
        {
            "id": "id1",
            "system": "PDOU"
        }
    ],
    "2and3": [
        {
            "id": "id1",
            "system": "PDOU"
        },
        {
            "id": "id2",
            "system": "PDOU"
        }
    ]
}