json / jq : multi-level grouping of sub-elements in an array - arrays

Question

i'm writing a script that needs to parse incoming json into line-by-line data, taking information from the json at multiple different levels. i'm using jq to parse the data.
the incoming json is an array of 'tasks'. each task [i.e. each element of the array] is an object that looks like this :
{
"inputData": {
"transfers": [
{
"source": {
"directory": "/path/to/source",
"filename": "somefile.mp3"
},
"target": {
"directory": "/path/to/target",
"filename": "somefile.mp3"
}
},
{
"source": {
"content": "<?xml version=\"1.0\" encoding=\"UTF-8\"?><delivery>content description</delivery>",
"encoding": "UTF-8"
},
"target": {
"directory": "/path/to/target",
"filename": "somefile.xml"
}
}
]
},
"outputData": {
"transferDuration": "00:00:37:10",
"transferLength": 187813298,
},
"updateDate": "2020-02-21T14:37:18.329Z",
"updateUser": "bob"
}
i want to read all of the tasks and, for each one, output a single line composed of the following fields :
task[n].inputData.transfers[].target.filename, task[n].outputData.transferLength, task[n].updateDate
i've got my filter chain to where it will choose the appropriate fields correctly, even to where it will pick the 'correct' single entry from amongst the multiple entries in the task[].inputData.transfers[] array, but when i try to get the output of more than a single element, the chain iterates over the array three times, and i get
task[0].inputData.transfers[].target.filename
task[1].inputData.transfers[].target.filename
task[2].inputData.transfers[].target.filename
...
task[n].inputData.transfers[].target.filename
then the results of the outputData.transferLength field for all elements,
then the results of the updateDate field for all elements.
here is my filter chain :
'(.tasks[].inputData.transfers[] | select(.target.filename | match("[Xx][Mm][Ll]$")).target.filename), .tasks[].outputData.transferLength, .tasks[].updateDate'
i'm thinking there must be some efficient way to group all of these multi-level elements together for each element of the array ; something like a 'with ...' clause, like with tasks[] : blablabla, but can't figure out how to do it. can anyone help ?

Answer 1

The JSON example contained a superfluous , that jq won't accept.
Your example filter chain appears to operate on .tasks[] even though the example appears to be only a single task. So it is not possible to rewrite what you have got into a functioning state. So rather than provide an exact answer to an inexact question, here is the first of the three parts of your filter chain revised:
.inputData.transfers | map(select(.target.filename | match("xml$"; "i")))
See this jqplay snippet.
Rather than write [ .xs[] | select(p) ], just write .xs | map(select(p)).

Answer 2

i finally found the answer. the trick was to pipe the .tasks[] into an expression where the parens were placed around the field elements as a group, which apparently will apply whatever is inside the parens to each element of the array individually, in sequence. then using #dmitry example as a guide, i also placed the elements inside right and left brackets to recreate array elements that i could then select, which could then be output onto 1 line each with | #csv. so the final chain that worked for me is :
.task[] | ([.inputData.transfers[].target.filename, .outputData.transferLength, .updateDate]) | [(.[0],.[2],.[3])] | #csv'
unfortunately i couldn't get match() to work in this invocation, nor sub() ; each of these caused jq to offer a useless error message just before it dumped core.
many thanks to the people who replied.