MongoDb nested array query for following relationship

Question

Say I have a User schema:

UserSchema = new Schema({
name:               {
                      first: { type: String, trim: true },
                      last:  { type: String, trim: true }
                    },
username:           { type: String, trim: true, required: true },
email:              { type: String, trim: true, required: true },
hashed_password:    { type: String, trim: true, required: true },
profile_image:      { type: String, trim: true, default: 'default' },
join_date:          { type: Date,     required:true },
userFollows:        [ {
                        status  : { type: String, enum: [
                            'following',
                            'followed_by'
                      ]},
                        added   : { type: Date,   required:true },
                        user    : { type: Schema.ObjectId, ref: 'User'}
                    } ]
})

I need to push a new userFollows in to this schema but I also need to check the user does not currently follow the user (duplicate entry) but am not sure how to perform this query

The current query I am attempting to use is:

User
.findOne(
        {  username: req.user.username },
        { "userFollows.user": { $not: req.body.userID } }
     )
.exec(function (err, currentUser) {

})

But it's not working.

I'd like to avoid looping through the currentUser.userFollows array after the query is performed and manually checking

Final userFollows object I need to push looks like this:

{
  _id: ObjectId("53073acd9256e81e4d7b5d8e"),
  status: "followed_by",
  added: ISODate("2014-02-21T11:38:53.828Z"),
  user: ObjectId("51c6ec9fedc1230700000007")
}

Just a guess, but something like findOne{ username: req.user.username, "userFollows.user": { $ne: req.body.userID } }) should work. The important difference is calling findOne with one object, not two. — Andreas Hultgren
– Andreas Hultgren, Commented Feb 21, 2014 at 12:51
I'm getting this error: {"code":"InternalError","message":"Cannot read property 'userFollows' of null"} with both my query and the one above — Ross J
– Ross J, Commented Feb 21, 2014 at 13:15

Asya Kamsky · Accepted Answer · 2014-02-24 09:16:49Z

There are two ways that you can do this update (in shell syntax):

db.users.update( 
     { "username": req.user.username },
     { $addToSet : { userFollows : { _id: ObjectId("53073acd9256e81e4d7b5d8e"),
                                     status: "followed_by",
                                     added: ISODate("2014-02-21T11:38:53.828Z"),
                                     user: ObjectId("51c6ec9fedc1230700000007")
                                   }
                   }
     }
)

which says, for this user, add to userFollows array this object (unless it's already there).

The other way to do it is:

db.users.update( 
     { "username": req.user.username, "userFollows.user": { $ne: req.body.userID } },
     { $push : { userFollows : { _id: ObjectId("53073acd9256e81e4d7b5d8e"),
                                     status: "followed_by",
                                     added: ISODate("2014-02-21T11:38:53.828Z"),
                                     user: ObjectId("51c6ec9fedc1230700000007")
                                   }
                   }
     }
)

which says: for this user, who doesn't already have this follower, $push this object.

Obviously you would fill in appropriate fields - I simply cut-n-paste some sample values from your question to show the full format.

Neil Lunn · Accepted Answer · 2014-02-21 13:20:18Z

0

Checkout this about adding data to nested array within an update query.

db.collection.update( 
    { username: req.user.username }, 
    { $addToSet: { "userFollows.user": req.user.usernameThatIAdd } }
 );

edited Feb 21, 2014 at 13:20

Neil Lunn

151k36 gold badges356 silver badges327 bronze badges

answered Feb 21, 2014 at 12:51

Stephen Henderson

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4 Comments

Ross J Over a year ago

Will this work if I need to add the status and added fields as well ? The final userFollows object looks like this: { status: "followed_by", added: ISODate("2014-02-21T11:38:53.828Z"), user: ObjectId("51c6ec9fedc1230700000007"), _id: ObjectId("53073acd9256e81e4d7b5d8e") }

WiredPrairie Over a year ago

userFollows is more than just a user name though. So, $addToSet as you've suggested won't work.

WiredPrairie Over a year ago

And, you'll find it won't actually work syntactically. You'll get an error can't append to array using string field name: user. You can't use the dot syntax with $addToSet.

Neil Lunn Over a year ago

Doubling @WiredPrairie this just will not work. And for the second time recently I ask. "Who is up-voting these completely untested and wrong answers?"

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