How to join JSON objects on particular fields using jq? - json

Question

I have following JSON structure:
{
"Reservations": [
{
"Id": "R-1",
"CustomerId": "1"
},
{
"Id": "R-2",
"CustomerId": "2"
}
],
"Customers": [
{
"Id": "1",
"Name": "customer 1"
},
{
"Id": "2",
"Name": "customer 2"
},
{
"Id": "3",
"Name": "customer 3"
}
]
}
I want to join Reservations with Customers and get something like this:
{
"ReservationId": "R-1",
"CustomerName": "customer 1"
}
{
"ReservationId": "R-2",
"CustomerName": "customer 2"
}
I've played with jq extensively, tried using multiple filters separated by comma, tried using variables, read the docs, but it seems like doing such a simple tasks is impossible with jq. Or, am I missing something?

Answer 1

Here's a simple solution using INDEX/2:
INDEX(.Customers[]; .Id) as $c
| .Reservations[]
| { ReservationId: .Id,
CustomerName: $c[.CustomerId].Name }
If your jq does not have INDEX/2 then now would be a good time to upgrade; otherwise, you can copy-and-paste its def from https://github.com/stedolan/jq/blob/master/src/builtin.jq, or you could use INDEX/3 as defined below.
INDEX/3
def INDEX(s; k; v):
reduce s as $x ({}; .[$x|k] = ($x|v));
INDEX(.Customers[]; .Id; .Name) as $c
| .Reservations[]
| { ReservationId: .Id,
CustomerName: $c[.CustomerId] }