Map arrays to objects with no common fields - json

Question

How might one use jq-1.5-1-a5b5cbe to join a filtered set of arrays from STDIN to a set of objects which contains no common fields, assuming that all elements will be in predictable order?
Standard Input (pre-slurpfile; generated by multiple GETs):
{"ref":"objA","arr":["alpha"]}
{"ref":"objB","arr":["bravo"]}
Existing File:
[{"name":"foo"},{"name":"bar"}]
Desired Output:
[{"name":"foo","arr":["alpha"]},{"name":"bar","arr":["bravo"]}]
Current Bash:
$ multiGET | jq --slurpfile stdin /dev/stdin '.[].arr = $stdin[].arr' file
[
{
"name": "foo",
"arr": [
"alpha"
]
},
{
"name": "bar",
"arr": [
"alpha"
]
}
]
[
{
"name": "foo",
"arr": [
"bravo"
]
},
{
"name": "bar",
"arr": [
"bravo"
]
}
]
Sidenote: I wasn't sure when to use pretty/compact JSON in this question; please comment with your opinion on best practice.

Answer 1

Get jq to read file before stdin, so that the first entity in file will be . and you can get everything else using inputs.
$ multiGET | jq -c '. as $objects
| [ foreach (inputs | {arr}) as $x (-1; .+1;
. as $i | $objects[$i] + $x
) ]' file -
[{"name":"foo","arr":["alpha"]},{"name":"bar","arr":["bravo"]}]

Answer 2

"Slurping" (whether using -s or --slurpfile) is sometimes necessary but rarely desirable, because of the memory requirements. So here's a solution that takes advantage of the fact that your multiGET produces a stream:
multiGET | jq -n --argjson objects '[{"name":"foo"},{"name":"bar"}]' '
$objects
| [foreach inputs as $in (-1; .+1;
. as $ix
| $objects[$ix] + ($in | del(.ref)))]
'
Here's a functional approach that might be appropriate if your stream was in fact already packaged as an array:
multiGET | jq -s --argjson objects '[{"name":"foo"},{"name":"bar"}]' '
[$objects, map(del(.ref))]
| transpose
| map(add)
'
If the $objects array is in a file or too big for the command line, I'd suggest using --argfile, even though it is technically deprecated.
If the $objects array is in a file, and if you want to avoid --argfile, you could still avoid slurping, e.g. by using the fact that unless -n is used, jq will automatically read one JSON entity from stdin:
(echo '[{"name":"foo"},{"name":"bar"}]';
multiGET) | jq '
. as $objects
| [foreach inputs as $in (-1; .+1;
. as $ix | $objects[$ix] + $in | del(.ref))]
'