Is there a way to use default in object construction with jq? - json

Question

I want to filter and assign a value from array based on a condition, and use default in case if array does not have the matched object.
Here is a sample object:
{
"array" : [
{
"id": "A",
"conversations": [
{
"conversation": "1",
"type": "good"
},
{
"conversation": "2",
"type": "bad"
}
]
},
{
"id": "B",
"conversations": [
{
"conversation": "3",
"type": "good"
},
{
"conversation": "4",
"type": "bad"
}
]
},
{
"id": "C",
"conversations": [
{
"conversation": "5",
"type": "bad"
},
{
"conversation": "6",
"type": "bad"
}
]
}
]
}
Required output:
{
"id": "A",
"goodConversation": "1"
}
{
"id": "B",
"goodConversation": "3"
},
{
"id": "C",
"goodConversation": null
}
echo of my input:
echo '{"array":[{"id":"A","conversations":[{"conversation":"1","type":"good"},{"conversation":"2","type":"bad"}]},{"id":"B","conversations":[{"conversation":"3","type":"good"},{"conversation":"4","type":"bad"}]},{"id":"C","conversations":[{"conversation":"5","type":"bad"},{"conversation":"6","type":"bad"}]}]}'
I tried running following jq
jq '.array[] | {id, "goodConversation": .conversations[] | select(.type == "good") | .conversation}'
Actual output:
{
"id": "A",
"goodConversation": "1"
}
{
"id": "B",
"goodConversation": "3"
}
since the object with id: "C" does not have any good conversation the whole object gets filtered out. Is there a way to create the output object which contains "C" with null as value?
Clarification:
"conversations" will have at most one good conversation.
I am using jq 1.5

Answer 1

One way to provide a default value is often to use the // "alternative" operator. Building on the foundations you've laid, you could write:
.array[]
| {id,
"goodConversation":
((.conversations[]
| select(.type == "good")
| .conversation) // null) }
If there is more than one "good" conversation, however, this may not be exactly what you want. If it's not, then consider using first, e.g.:
.array[]
| {id,
"goodConversation":
( first(.conversations[]
| select(.type == "good")
| .conversation) // null)}