How to get subdocuments of multiple documents in mongoose - mongodb

Question

I have a Module called Organisation with an array calls users in it that contains UserSchema objects. Now i need a query to get all users from all organisation documents in one array.
As you can see I am a beginner in mongodb and normaly use sql
But without joins I don´t know what to do.
OrganisationModule:
const OrganisationSchema = new Schema({
name: { type: String, required: true },
users: [UserSchema],
version: String,
});
module.exports.Organisation = mongoose.model('Organisation', OrganisationSchema);
UserSchema:
module.exports.UserSchema = new Schema({
name: String,
roles: [String]
})
My first try:
routes.get('/', (req, res, next) => {
Organisation.find().populate('users').exec((err, users) => {
if (err) res.json(err.message)
else { res.json(users) }
});
The result:
[
{
"users": [
{
"roles": [ "coordinator" ],
"_id": "5aafcf80dd248f7ef86e0512",
"name": "Peter"
"__v": 0
}
],
"_id": "5aafcf80dd248f7ef86e05cf",
"name": "DEFAULT",
"__v": 1
},
{
"users": [
{
"roles": [ "admin", "coordinator" ],
"_id": "5aafcf80dd248f7ef86e0500",
"name": "Max"
"__v": 0
}
],
"_id": "5aafcf80dd248f7ef86e05ce",
"name": "Organisation_01",
"__v": 1
}
]
What I need:
[
{
"roles": [ "coordinator" ],
"_id": "5aafcf80dd248f7ef86e0512",
"name": "Peter"
"__v": 0
},
{
"roles": [ "admin", "coordinator" ],
"_id": "5aafcf80dd248f7ef86e0500",
"name": "Max"
"__v": 0
}
]

Answer 1

This
Organization.find(
{},
{_id: 0, users: 1}
)
Will return
[
{
users: {
roles: ['coordinator'],
_id: '5aafcf80dd248f7ef86e0512',
name: 'Peter',
....
},
},
{
users: {
roles: ['admin', 'coordinator'],
_id: '5aafcf80dd248f7ef86e0500',
name: 'Max',
....
},
},
];
This is not precisely what you want, but it is what I have found that most closely matches your need.
You can find more information here :
https://stackoverflow.com/a/42558955/11120444
https://stackoverflow.com/a/9601614/11120444
Else, there is an other approach
// Meaby you will need to add await
const users = Organization.find({}).map((item: any) => item.users);

Answer 2

In mongodb you can use $lookup to perform that operation.
Please study $lookup here: https://docs.mongodb.com/manual/reference/operator/aggregation/lookup/
In mongoose you can use populate()
For example:
Organization.find().populate('users')
Study Mongoose's Populate here: http://mongoosejs.com/docs/populate.html