Mongodb query select performing - mongodb

Question

I'm trying to get this result:
{
facebookId: [
"123123", "321321", "999999"
]
}
But i get this result:
{
\"mobileUser\": {
\"facebookId\": \"1547339005533880\"
}
},
{
\"mobileUser\": {
\"facebookId\": \"958277234198503\"
}
},
{
\"mobileUser\": {
\"facebookId\": \"10201611922458772\"
}
}
My model:
var roomModelSchema = mongoose.Schema({
roomId: { type: String, index: true },
mobileUser: {
socketId: String,
facebookId: { type: String, index: true },
email: String,
name: String,
photoUrl: String,
genderType: String,
birthday: Date,
city: String,
likeCount: Number,
insertDate: Date
},
insertDate: Date
})
My query is:
Room.find({ "roomId": req.query.roomId }).select("mobileUser.facebookId -_id").exec(function(err, users) {
});
I'm work on it to know how mongodb query works. Because if i use to build this query in sql it's very easy. I have difficulties to understand it.

Answer 1

If you think about MongoDb in terms of SQL RDBMS, each mongodb document corresponds to row in SQL DB.
So for example if you execute in SQL
select * from myTable
you will get
facebookID | name | city
--------------------------------
13453 | A | A
2213 | B | B
312321 | C | C
and if you do the simialr query in mongo
db.myTable.find({})
you will get
{facebookId: 13454, name: A, city: A},
{facebookId: 2213, name: B, city: B},
{facebookId: 312321, name: C, city: c},
So now if you query for one field and execute in SQL
select facebookId from myTable
you will get
facebookID
----------
13453
2213
312321
And in mongoDb, if you execute
db.myTable.find({}, {id:false, faceBookId: true})
{id:false, faceBookId: true} - correspond to select methods from Mongoose. It specifies what fields should be included in documents
you will get
{facebookId: 13454},
{facebookId: 2213},
{facebookId: 312321},
If you would like to get these fields from multiple documents and output single document with facebookId field that contains all values, you can use aggregate framework
db.myTable.aggregate(
{$group:{_id:null, facebookId:{$addToSet:'$Name'}}}
)
This will return:
{
_id: null,
facebookId: [
"13454", "2213", "312321"
]
}