jq: Conditional insert using "lookup" & "target" JSON objects - json

Question

I'm trying to improve a bash script I wrote using jq (Python version), but can't quite get the conditional nature of the task at hand to work.
The task: insert array from one JSON object ("lookup") into another ("target") only if the key of the "lookup" matches a particular "higher-level" value in the "target". Assume that the two JSON objects are in lookup.json and target.json, respectively.
A minimal example to make this clearer:
"Lookup" JSON:
{
"table_one": [
"a_col_1",
"a_col_2"
],
"table_two": [
"b_col_1",
"b_col_2",
"b_col_3"
]
}
"Target" JSON:
{
"top_level": [
{
"name": "table_one",
"tests": [
{
"test_1": {
"param_1": "some_param"
}
},
{
"test_2": {
"param_1": "another_param"
}
}]
},
{
"name": "table_two",
"tests": [
{
"test_1": {
"param_1": "some_param"
}
},
{
"test_2": {
"param_1": "another_param"
}
}
]
}
]
}
I want the output to be:
{
"top_level": [{
"name": "table_one",
"tests": [{
"test_1": {
"param_1": "some_param"
}
},
{
"test_2": {
"param_1": "another_param",
"param_2": [
"a_col_1",
"a_col_2"
]
}
},
{
"name": "table_two",
"tests": [{
"test_1": {
"param_1": "some_param"
}
},
{
"test_2": {
"param_1": "another_param",
"param_2": [
"b_col_1",
"b_col_2",
"b_col_3"
]
}
}
]
}
]
}
]
}
Hopefully, that makes sense. Early attempts slurped both JSON blobs and assigned them to two variables. I'm trying to select for a match on [roughly] ($lookup | keys[]) == $target.top_level.name, but I can't quite get this match or the subsequent the array insert working.
Any advice is well-received!

Answer 1

Assuming the JSON samples have been corrected, and that the following program is in the file "target.jq", the invocation:
jq --argfile lookup lookup.json -f target.jq target.json
produces the expected result.
target.jq
.top_level |= map(
$lookup[.name] as $value
| .tests |= map(
if has("test_2")
then .test_2.param_2 = $value
else . end) )
Caveat
Since --argfile is officially deprecated, you might wish to choose an alternative method of passing in the contents of lookup.json, but --argfile is supported by all extant versions of jq as of this writing.

Answer 2

The jq answer is already given, but the ask itself is so fascinating - it requires a cross-lookup from a source file into the file being inserted, so I could not help providing also an alternative solution using jtc utility:
<target.json jtc -w'<name>l:<N>v[-1][tests][-1:][0]' \
-i file.json -i'<N>t:' -T'{"param_2":{{}}}'
A brief overlook of the used options:
-w'<name>l:<N>v[-1][tests][-1:][0]' - selects points of insertions in the source (target.json) by finding and memorizing into namespace N keys to be looked up in the inserted file, then rolling back 1 level up in the JSON tree, selecting tests label, then the last entry in it and finally addressing a 1st element of the last one
-i file.json make an insertion from the file
-i'<N>t:' - this walk over file.json finds recursively a tag (label) preserved in the namespace N from the respective walk -w (if not this insert option with the walk argument, then the whole file would get inserted into the insertion points -w..)
-T'{"param_2":{{}}}' - finally, a template operation is applied onto the insertion result transforming found entry (in file.json) into the one with the right label
PS. I'm the developer of the jtc - multithreading JSON processing utility for unix.
PPS. the disclaimer is required by SO.