Mongoose Multi Update req.body
Label.update({'_id': { $in: post.labelIds }}, {$addToSet: {postIds:req.body.id}}, {multi: true}).exec()
Relieved Rattlesnake
Label.update({'_id': { $in: post.labelIds }}, {$addToSet: {postIds:req.body.id}}, {multi: true}).exec()