Using pull in mongoose model - node.js

Question

Should this work? I am trying to remove a single subdocument (following) from a document (this) in the UserSchema model.
UserSchema.methods.unFollow = function( id ) {
var user = this
return Q.Promise( function ( resolve, reject, notify ) {
var unFollow = user.following.pull( { 'user': id } )
console.log( unFollow )
user.save( function ( error, result ) {
resolve( result )
})
})
}
These are the schemas:
var Follows = new mongoose.Schema({
user: String,
added: Number
})
var UserSchema = new mongoose.Schema({
username: {
type: String,
required: true,
unique: true
},
following: [ Follows ]
})
user-controller.js
/*
Unfollow user.
*/
exports.unFollow = function ( req, res ) {
User.findOne( { token: req.token }, function ( error, user ) {
user.unfollow( req.body.id )
.onResolve( function ( err, result ) {
if ( err || !result ) return res.status( 500 ).json( "User could not be unfollowed." )
return res.status( 200 ).json( "User unfollowed." )
})
})
}
user-model.js
/*
Unfollow a user.
*/
UserSchema.method( 'unfollow', function unfollow ( id ) {
this.following.pull( { user: id } )
return this.save()
})

Answer 1

You generally assign methods using the method function:
UserSchema.method('unFollow', function unFollow(id) {
var user = this;
user.following.pull({_id: id});
// Returns a promise in Mongoose 4.X
return user.save();
});
Also, as noted, you don't need to use Q as save will return a mongoose promise.
UPDATE: Mongoose's array pull method will work with matching primitive values but with subdocument objects it will only match on _id.
UPDATE #2: I just noticed your updated question shows that your controller is doing a lookup first, modifying the returned document and then saving the document back to the server. Why not create a static rather than a method to do what you want? This has the added bonus of being a single call to the DB rather than two per operation.
Example:
UserSchema.static('unfollow', function unfollow(token, id, cb) {
var User = this;
// Returns a promise in Mongoose 4.X
// or call cb if provided
return User.findOneAndUpdate({token: token}, {$pull: {follows: {user: id}}}, {new: true}).exec(cb);
});
User.unfollow(req.token, req.body.id).onResolve(function (err, result) {
if (err || !result) { return res.status(500).json({msg: 'User could not be unfollowed.'}); }
return res.status(200).json({msg: 'User unfollowed.'})
});
Bonus follow static:
UserSchema.static('follow', function follow(token, id, cb) {
var User = this;
// Returns a promise in Mongoose 4.X
// or call cb if provided
return User.findOneAndUpdate({token: token}, {$push: {follows: {user: id}}}, {new: true}).exec(cb);
});
User.follow(req.token, req.body.id).onResolve(function (err, result) {
if (err || !result) { return res.status(500).json({msg: 'User could not be followed.'}); }
return res.status(200).json({msg: 'User followed.'})
});

Answer 2

NOTE: Used in "mongoose": "^5.12.13".
As for today June 22nd, 2021, you can use $in and $pull mongodb operators to remove items from an array of documents :
Parent Document :
{
"name": "June Grocery",
"description": "Some description",
"createdDate": "2021-06-09T20:17:29.029Z",
"_id": "60c5f64f0041190ad312b419",
"items": [],
"budget": 1500,
"owner": "60a97ea7c4d629866c1d99d1",
}
Documents in Items array :
{
"category": "Fruits",
"bought": false,
"id": "60ada26be8bdbf195887acc1",
"name": "Kiwi",
"price": 0,
"quantity": 1
},
{
"category": "Toiletry",
"bought": false,
"id": "60b92dd67ae0934c8dfce126",
"name": "Toilet Paper",
"price": 0,
"quantity": 1
},
{
"category": "Toiletry",
"bought": false,
"id": "60b92fe97ae0934c8dfce127",
"name": "Toothpaste",
"price": 0,
"quantity": 1
},
{
"category": "Toiletry",
"bought": false,
"id": "60b92ffb7ae0934c8dfce128",
"name": "Mouthwash",
"price": 0,
"quantity": 1
},
{
"category": "Toiletry",
"bought": false,
"id": "60b931fa7ae0934c8dfce12d",
"name": "Body Soap",
"price": 0,
"quantity": 1
},
{
"category": "Fruit",
"bought": false,
"id": "60b9300c7ae0934c8dfce129",
"name": "Banana",
"price": 0,
"quantity": 1
},
{
"category": "Vegetable",
"bought": false,
"id": "60b930347ae0934c8dfce12a",
"name": "Sombe",
"price": 0,
"quantity": 1
},
Query :
MyModel.updateMany(
{ _id: yourDocumentId },
{ $pull: { items: { id: { $in: itemIds } } } },
{ multi: true }
);
Note: ItemIds is an array of ObjectId. See below :
[
'60ada26be8bdbf195887acc1',
'60b930347ae0934c8dfce12a',
'60b9300c7ae0934c8dfce129'
]