Where to exactly use parenthesis "()" in data weave language

Question

I have a code like this

 {name: 'Data Weave'} mapObject {(upper $$ ) : $}

which dynamically takes map object and upper cases key. below is the output

   {
"NAME": "Data Weave"
   }

When I remove parenthesis that are enclosed to "upper" keyword. data weave is throwing error like this.

I have a syntax confusion exactly where to use parenthesis in the data weave language. in the above code why there is need to use parenthesis. how the compiler interprets the conditions or expression that are enclosed between parenthesis.

Sébastien Colas · Accepted Answer · 2019-10-31T15:47:27.663

5

%dw 2.0
output application/json
---
{name: 'Data Weave'} mapObject {(upper($$) ) : $}

I think you just forget parenthesis for the upper fonction. parenthesis surrounding upper fonction are still needing to say to DW the key is not static but dynamically evaluated. To summarize:

upper($$) put your $$ in upper case => Parenthesis are here to pass arguments to the function
(upper($$)) because the key is the result of an evaluation => Parenthesis are here to evaluate an expression and return the result

edited Oct 31 '19 at 15:47

answered Oct 31 '19 at 15:35

Sébastien Colas

424
2
6

am using "upper" a predefined function and am not using parenthesis to enclose $$. am getting expected out put – kushma gonna Oct 31 '19 at 16:31
You just have to remember to call a function it is really simple: ```funtionName(arg1,arg2,arg3...)``` – Sébastien Colas Oct 31 '19 at 17:06
For 2 arguments function there is 2 ways to write it: ```functionName(arg1,arg2)``` or ```arg1 functionName arg2``` – Sébastien Colas Oct 31 '19 at 17:07

score 2 · Answer 2 · answered Oct 31 '19 at 19:33

AFAIK there are three different meanings to parenthesis in DW:

1) Precedence operators eg (1 + 1) * 10

2) Field evaluators, your use case and what @Sebastien Colas is describing.

3) Destructors of Objects and Arrays of objects into pairs of keys and values WHEN they appear on their own inside {}:

%dw 2.0
output application/dw
var d = [
    {
        a: 1,
        b: 2,
        c: 3
    },
    {
        d: 4,
        e: 5
    }
]
---
[
    {
        (d)
    },
    {
        (d[1]),
        f: 6
    }   
]

Where to exactly use parenthesis "()" in data weave language

2 Answers2