N.B.: This is the first javascript function I've written. My question is inspired by another question inquiring about recursive descent within a MongoDB document.
I tried the function on jsfiddle.net and it works, but when I try it on mongoplayground.net, it doesn't work.
Input collection:
[
{
"_id": 0,
"text": "Node1",
"children": [
{
"text": "Node2",
"children": []
},
{
"text": "Node3",
"children": [
{
"text": "Node4",
"children": [
{
"text": "Node5",
"children": []
},
{
"text": "Node6",
"children": []
}
]
},
{
"text": "Node7",
"children": []
}
]
}
]
}
]
mongoplayground.net aggregation pipeline:
db.collection.aggregate([
{
"$set": {
"texts": {
"$function": {
"body": "function(t, n) {function drill(t, n) {if (n.length > 0) {for (let elem of n) {t.push(elem.text); drill(t, elem.children)}} return t};drill(t,n)}",
"args": [
[
"$text"
],
"$children"
],
"lang": "js"
}
}
}
}
])
jsfiddle.net outputs the desired result, ["Node1", "Node2", "Node3", "Node4", "Node5", "Node6", "Node7"], but mongoplayground.net sets "texts" to null.
Is there a way to fix the MongoDB "$function" or is this a limitation of mongoplayground.net or MongoDB?
How about just removing the external function to get your desired results:
db.collection.aggregate([
{
"$addFields": {
"texts": {
"$function": {
"body": "function drill(t, n) {if (n.length > 0) {for (let elem of n) {t.push(elem.text); drill(t, elem.children)}} return t};",
"args": [
[
"$text"
],
"$children"
],
"lang": "js"
}
}
}
}
])
You can see it works here