Adding Element to array of element in json using jq - arrays

Question

Ok, i spent way to much time on this.
Using jq, i want to test if an element exist in an array, if yes being able to mofify this element, if not adding this element to that array
I have read
Update one value in array of dicts, using jq
How to check if element exists in array with jq
Which gave hints But i am stuck
Let say i have a json file like :
{
"LOGIN":"user",
"COPY": [
{
"CHAINLIST":"chain1",
"ELEMENT": [ "element1-1","element1-2" ]
},
{
"CHAINLIST":"chain2",
"ELEMENT": [ "element2-1","element2-2" ]
}
]
}
I Would like to add elements to the COPY array based in the CHAINLIST id , let say those 3 elements :
//ELEM A
{
"CHAINLIST":"chain3",
"ELEMENT": [ "element3-1" ]
}
//ELEM B
{
"CHAINLIST":"chain2",
"ELEMENT": [ "element2-1","element2-3" ]
}
//ELEM C
{
"CHAINLIST":"chain1",
"ELEMENT": [ "element1-1","element1-2" ]
}
ELEM A has the CHAINLIST id chain3 who doesn't exit in the COPY Array _> let's add it
ELEM B Is already present in the COPY aray, I want to update the ELEMENT array
content with the new value
ELEM C Already exist and is up to date, i don't need to do anything.
In my example the final json object would be
{
"LOGIN":"user",
"COPY": [
{
"CHAINLIST":"chain1",
"ELEMENT": [ "element1-1","element1-2" ]
},
{
"CHAINLIST":"chain2",
"ELEMENT": [ "element2-1","element2-2","element2-3" ]
},
{
"CHAINLIST":"chain3",
"ELEMENT": [ "element3-1"]
}
]
}
I am using jq The procedure to add the element Elem to the object Obj would be :
Elem.CHAINLIST exist in Obj.COPY [] ?
yes : add Elem.ELEMENT to Obj.ELEMENT[] with unique to qvoid duplicates
no : add Elem to Obj.COPY[]
The best i get is
(if .COPY[]? | select (.CHAINLIST=="chain3") == "" then . else .COPY[.COPY | length ] |= . + { "CHAINLIST":"chain3","ELEMENT":[ "element3-1"]} end )
But select (.CHAINLIST=="chain3") == "" return nothing I i can figure out how to test if empty.
Thank you for your time !

Answer 1

The following solution uses the built-in function INDEX/2 to create convenient and efficient representations
of the collections of CHAINLIST-ELEMENT objects, together with a bespoke function, augment/1, for combining elements.
It is assumed that the objects defining the updates are presented as an array in the file edits.json.
< input.json jq --argfile edits edits.json '
# Use `unique` to combine the .ELEMENT fields
def augment($b):
reduce ($b|keys_unsorted[]) as $key (.;
.[$key].ELEMENT = (.[$key].ELEMENT + $b[$key].ELEMENT | unique));
(INDEX($edits[];.CHAINLIST) | map_values(del(.CHAINLIST))) as $edits
| (INDEX(.COPY[]; .CHAINLIST) | map_values(del(.CHAINLIST))) as $COPY
| .COPY |= ($COPY
| augment($edits)
| to_entries
| map( { CHAINLIST: .key, ELEMENT: .value.ELEMENT} ))
Output: as specified in the question.
Note: if the objects defining the updates are presented as a sequence of objects in a file, you could use the above solution with --slurpfile instead of --argfile.