jq: output values of ids instead of numbers - json

Question

Here's my input json:
{
"channels": [
{ "id": 1, "name": "Pop"},
{ "id": 2, "name": "Rock"}
],
"links": [
{ "id": 2, "streams": [ {"url": "http://example.com/rock"} ] },
{ "id": 1, "streams": [ {"url": "http://example.com/pop"} ] }
]
}
This is what I want as an output:
"http://example.com/pop"
"Pop"
"http://example.com/rock"
"Rock"
So I need jq to replace .channels[].id with .links[].streams[0].url based on .links[].id
I don't know if it's right, but this is how I managed to output the urls:
(.channels[].id | tostring) as $ids | [.links[]] | map({(.id | tostring): .streams[0].url}) | add as $urls | $urls[$ids]
"http://example.com/pop"
"http://example.com/rock"
The question is, how do I add .channels[].name to it?

Answer 1

You sometimes have to be careful what you ask for, but this will produce the result you said you want:
.channels[] as $channel
| $channel.name,
(.links[] | select(.id == $channel.id) | .streams[0].url)
Output for the given input:
"Pop"
"http://example.com/pop"
"Rock"
"http://example.com/rock"

Answer 2

Here is a solution which uses reduce and setpath to make a $urls lookup table from .links and then scans .channels generating corresponding urls and names.
(
reduce .links[] as $l (
{};
setpath([ $l.id|tostring ]; [$l.streams[].url])
)
) as $urls
| .channels[]
| $urls[ .id|tostring ][], .name
If multiple urls are present in the "streams" attribute this will
print them all before printing the name. e.g. if the input is
{
"channels": [
{ "id": 1, "name": "Pop"},
{ "id": 2, "name": "Rock"}
],
"links": [
{ "id": 2, "streams": [ {"url": "http://example.com/rock"},
{"url": "http://example.com/hardrock"} ] },
{ "id": 1, "streams": [ {"url": "http://example.com/pop"} ] }
]
}
the output will be
"http://example.com/pop"
"Pop"
"http://example.com/rock"
"http://example.com/hardrock"
"Rock"