Mongoose - Search inside nested array with no limits - mongodb

Question

My mongodb collection is stores records of groups which can have subgroups, which can further have sub-sub groups and there will not be any limits of nesting of this sub-groups. Is there anyway in mongoose to find a group name that resides in nth level?
My collection structure looks like the following, so suppose if i want to find if "My Group" has a subgroup named "My Group 1001", how am I supposed to find it?
{
"id": "60c18d4ce973fc139f23bf93",
"name": "My Group",
"subgroups": [
{
"id": "70c18d4ce973fc139f23bf93",
"name": "My Group 2",
"subgroups": [
{
"id": "80c18d4ce973fc139f23bf93",
"name": "My Group 3",
"subgroups": [
{
"id": "90c18d4ce973fc139f23bf93",
"name": "My Group 4",
"subgroups": [ ... ],
}
]
}
]
}
]
}
The other solutions that I found on stackoverflow suggested that it can be achieved using the dot notation for eg,
$or: [
{"name": "My Group 1001"},
{"subgroups.name": "My Group 1001"},
{"subgroups.subgroups.name": "My Group 1001"},
...
]
But since in my case the level is not known hence I cannot use the above pattern.

Answer 1

Mongodb is not an ideal tool for recursive operations.
Not recommended, but you can use $function to do the job with javascript:
db.collection.find({
$expr: {
$function: {
body: "function(subgroups, topName) { let recursiveSearch = function(sg){ if(!sg) {return false}; return sg.some(function(subdoc) {return subdoc.name == 'My Group 1001' || recursiveSearch(subdoc.subgroups)})}; return topName == 'My Group 1001' || recursiveSearch(subgroups);}",
args: [
"$subgroups",
"$name"
],
lang: "js"
}
}
})
The function alone formatted for readability:
function(subgroups, topName) {
let recursiveSearch = function (sg) {
if (!sg) { return false };
return sg.some(function (subdoc) {
return subdoc.name == 'My Group 1001' || recursiveSearch(subdoc.subgroups)
})
};
return topName == 'My Group 1001' || recursiveSearch(subgroups);
}
There is no tail recursion so I imagine it may blow up if it exhaust call stack. Didn't test it myself though.
If you have luxury of changing data format, consider adding a top level "names" flat array of all names from the nested documents. It will add some overhead to the application logic to keep it up to date on each update. The search will be as simple as
db.collection.find({"names": "My Group 1001"})
As an additional bonus you will be able to benefit from multikey indexes

Answer 2

Maybe finding keys with values can help you:
const flattenObj = (obj, parent, res = {}) => {
for (let key in obj) {
let propName = parent ? parent + '.' + key : key;
if (typeof obj[key] == 'object') {
flattenObj(obj[key], propName, res);
} else {
res[propName] = obj[key];
}
}
return res;
}
const obj = {
"id": "60c18d4ce973fc139f23bf93",
"name": "My Group",
"subgroups": [
{
"id": "70c18d4ce973fc139f23bf93",
"name": "My Group 2",
"subgroups": [
{
"id": "80c18d4ce973fc139f23bf93",
"name": "My Group 3",
"subgroups": [
{
"id": "90c18d4ce973fc139f23bf93",
"name": "My Group 4"
}
]
}
]
}
]
}
const dotNotation = flattenObj(obj);
// Finding keys from object by a specific value
const key1 = Object.keys(dotNotation).find(key => dotNotation[key] === 'My Group 2');
const key2 = Object.keys(dotNotation).find(key => dotNotation[key] === 'My Group 3');
const key3 = Object.keys(dotNotation).find(key => dotNotation[key] === 'My Group 4');
console.log(`Key of 'My Group 2': ` + key1);
console.log(`Key of 'My Group 3': ` + key2);
console.log(`Key of 'My Group 4': ` + key3);