MongoDB querying references with additonal information - mongodb

Question

I am storing data of organizations in the following document structure:
{
"_id":ObjectId("52ffc33cd85242f436000001"),
"name": "NASA",
"users" : [
{
"_id" : ObjectId("5629f0b20fe85c57ed459913"),
"level" : "organization_lead"
},
{
"_id" : ObjectId("5629ff550fe85c57ed459914"),
"level" : "team_member"
}
]
}
Users are in another collection and look like this:
{
"_id" : ObjectId("5629ff550fe85c57ed459914"),
"email" : "bob#email.com",
"firstname" : "Bob",
"lastname" : "Green",
}
What would be the most efficient way to get a list of user documents belonging to a specific organization?
If I had only the _id's in the users array I would just pass that array to another query to get the users but what should I do in this situation? Or is there a better way to have a reference that has additional information?

Answer 1

Use the forEach() method of the find() cursor for the organisation collection to iterate over, access the documents in the loop and call the findOne() method to get the full user document of each user _id, as in the following example:
db.organisation.find({ "name": "NASA", "users.0": { "$exists": true } }).forEach(function(doc){
var updatedUsers = doc.users.map(function(u){
var user = db.users.findOne({"_id": u._id});
user["level"] = u.level;
return user;
}
doc.users = updatedUsers;
printjson(doc);
})

Answer 2

Use populate,
db.organisation.findOne({ "name": "NASA"}, function(err, response) {
db.Users.populate(response.user, {'path': _id, 'select': 'firstname lastname email'}, function(err, populatedUserData) {
console.log(populatedUserData);
});
});
Output will be,
[{
"_id":ObjectId("52ffc33cd85242f436000001"),
"name": "NASA",
"users" : [
{
"_id" : [{
"_id" : ObjectId("5629f0b20fe85c57ed459913"),,
"email" : "laurem#email.com",
"firstname" : "laurem",
"lastname" : "Ipsum"
}],
"level" : "organization_lead"
},
{
"_id" : [{
"_id" : ObjectId("5629ff550fe85c57ed459914"),
"email" : "bob#email.com",
"firstname" : "Bob",
"lastname" : "Green"
}],
"level" : "team_member"
}
]}]