Mongodb lookup like search: local field as array of objects - mongodb

Question

I have two collections userProfile and skills,
Eg:userProfile
{
"_id": "5f72c6d4e23732390c96b031",
"name":"name"
"other_skills": [
"1","2"
],
"primary_skills": [
{
"_id": "607ffd1549e13876fef7f2c5",
"years": 4.5,
"skill_id": "1"
},
{
"_id": "607ffd1549e13876fef7f2c6",
"years": 2,
"skill_id": "2"
},
{
"_id": "607ffd1549e13876fef7f2c7",
"years": 1,
"skill_id": "3"
}
]
}
Eg:Skills
{
"_id":1,
"name": "Ruby on Rails",
}
{
"_id":2,
"name": "PHP",
}
{
"_id":3,
"name": "php",
}
I want to retrieve the userprofile based on the skills
eg: input of skill php i want to retrieve the userprofiles that matches either in primary_skills or other_skills
But I got confused about the implementation, I think it can do with pipeline in lookup and the elemMatch. This is the query I tried so far
const skills = ['php','PHP']
userProfile.aggrigate([{
$lookup:{
from:'skills',
let:{'primary_skills':'$primary_skills'},
pipeline:[
{
$match:{
primary_skills:{
$elemMatch:{
name:'' //not sure how to write match
}
}
}
}
]
}
}])
Can somebody help me with this, Thanks in advance

Answer 1

I'll first show you how to correct your pipeline to work, however this approach is very inefficient as you will have to $lookup on every single user in your db which is obviously a lot of overhead.
Here is how to properly match your condition:
const skills = ['php','PHP']
db.userProfile.aggregate([
{
$lookup: {
from: "skills",
let: {
"primary_skills": {
$map: {
input: "$primary_skills",
as: "skill",
in: "$$skill.skill_id"
}
},
"other_skills": "$other_skills"
},
pipeline: [
{
$match: {
$expr: {
"$in": [
"$_id",
{
"$concatArrays": [
"$$other_skills",
"$$primary_skills"
]
}
]
}
}
}
],
as: "skills"
}
},
{
$match: {
'skills.name': {$in: skills}
}
}
])
Mongo Playground
As I've said I recommend you do not do this. what I suggest you do is split it into 2 calls, first fetch the relevant skill ids. and then query on users.
By doing this you can also utilize indexes for much faster queries, like so:
const skills = ['php', 'PHP'];
const matchedSkillIds = await skills.distinct('_id', {name: {$in: skills}});
const users = await userProfile.find({
$or: [
{
'primary_skills.skill_id': {$in: matchedSkillIds}
},
{
'other_skills': {$in: matchedSkillIds}
}
]
})
Finally if you do insist on doing it in one query at the very least start the pipeline from the skill collection.