How do I merge based on a missing elements with JQ? - bash

Question

I have two JSON files that I am working with: dest_sr.json and src_templates.json
What I would like to is create a new JSON object that combines keys from JSON object #1 (specifically the Template_SR key) and JSON object #2 (the Template_Name and Template_ID keys), but only when a VM-Template cannot be found on Pool_ID that matches on both object #1 and object #2
For the two given JSON objects:
dest_sr.json:
{
"Type": "pool",
"Pool_ID": "adb58e84",
"Template_SR": "fc820294"
}
{
"Type": "pool",
"Pool_ID": "d2dea684",
"Template_SR": "313f2a07"
}
src_templates.json:
{
"Type": "VM-template",
"Template_Name": "CentOS 7 CloudInit V1",
"Template_ID": "9b1833a3",
"Pool_ID": "adb58e84"
}
I would like to create a new JSON object that looks like this:
{
"Template_ID",:"9b1833a3",
"Template_SR":"313f2a07",
"Template_Name":"CentOS 7 CloudInit V1",
}
Using Stackoverflow I was able to hack together a hashJoin from examples that looks like this, where it performs a hashJoin on the .Pool_ID attribute to create a new object:
# hashJoin(a1; a2; field) expects a1 and a2 to be arrays of JSON objects
# and that for each of the objects, the field value is a string.
# A relational join is performed on "field".
def hashJoin(a1; a2; field):
# hash phase:
(reduce a1[] as $o ({}; . + { ($o | field): $o } )) as $h1
| (reduce a2[] as $o ({}; . + { ($o | field): $o } )) as $h2
# join phase:
| reduce ($h1|keys[]) as $key
([]; if $h2|has($key) then . + [ $h1[$key] + $h2[$key] ] else . end) ;
hashJoin( $file1; $file2; .Pool_ID)[]
When I call JQ to perform the hashJoin, I get a new object that looks like this:
/tmp $ jq -nc --slurpfile file1 /tmp/dest_sr.json --slurpfile file2 /tmp/src_templates.json -f hashJoinSimple.jq
{
"Type":"VM-template",
"Pool_ID":"adb58e84",
"Template_SR":"fc820294",
"Template_Name":"CentOS 7 CloudInit V1",
"Template_ID":"9b1833a3"
}
Is there any way I can write my merge so that the object would look like this?
{
"Type":"VM-template",
"Pool_ID":"d2dea684",
"Template_SR":"fc820294",
"Template_Name":"CentOS 7 CloudInit V1",
"Template_ID":"9b1833a3"
}

Answer 1

I think given your particular inputs and your desired result, I don't think the hashing is necessary. It seems like all you need to do is select the inputs from dest_sr.json where it doesn't match the id in src_templates.json, then combine it with the desired values from the template.
$ jq --argfile template src_templates.json '
select(.Pool_ID != $template.Pool_ID) + ($template|{Template_Name,Template_ID})
' dest_sr.json