Using Mongoose / MongoDB $addToSet functionality on array of objects

Question

say I have this array property ('articles') on a Mongoose schema:

articles: [ 

 {
  kind: 'bear',
  hashtag: 'foo'    
 },

 {
  kind: 'llama',
  hashtag: 'baz',
  },

 {
  kind: 'sheep',
  hashtag: 'bar',
  }

]

how can I use

$addToSet https://docs.mongodb.org/manual/reference/operator/update/addToSet/

to add to this array by checking the value of hashtag to see if it's unique?

For example, if I want to add the following object to the above array, I want Mongo to 'reject' it as a duplicate:

{
  kind: 'tortoise',
  hashtag: 'foo'

}

because hashtag=foo has already been taken.

The problem is that I only know how to use $addToSet with simple arrays of integers...

for example, if articles looked like this:

articles: [ 1 , 5 , 4, 2]

I would use $addToSet like this:

var data = {

    "$addToSet": {
     "articles": 9
   }

}

model.update(data);

but how can I accomplish the same thing with an array of objects where the unique field is a string, in this case 'hashtag'? The docs don't make this clear and it seems like I have searched everywhere..

thanks

Sede · Accepted Answer · 2020-05-18 15:26:13Z

54

You need to use the $ne operator.

var data = { 'kind': 'tortoise', 'hashtag': 'foo' };
Model.update(
    { 'articles.hashtag': { '$ne': 'foo' } }, 
    { '$addToSet': { 'articles': data } }
)

This will update the document only if there is no sub document in the "article" array with the value of hashtag equals to "foo".

As @BlakesSeven mentioned in the comment

The $addToSet becomes irrelevant once you are testing for the presence of one of the values, so this may as well be a $push for code clarity. But the principle is correct since $addToSet works on the whole object and not just part of it.

Model.update({ 
    { 'articles.hashtag': { '$ne': 'foo' } }, 
    { '$push': {'articles':  data } }
)

edited May 18, 2020 at 15:26

answered Nov 6, 2015 at 23:43

Sede

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8 Comments

Abhinav Saini Over a year ago

What if the object contains "_id" field? Will it still require '$ne' operator to check duplicity?

Pavan Vora Over a year ago

@styvane What if instead of matching with only hashtag I want to match with "article.kind" and "article.hashtg" and then add to set if the perfect match not exist

Sede Over a year ago

@PavanVora, you could you {'articles.hastag': {'$ne': 'cats'}, 'articles.kind': {'$ne': 'struct'}} in the filter.

Macindows Over a year ago

@PavanVora If you're looking for perfect matches you could simply use $addToSet itself

Macindows Over a year ago

@PavanVora Yes, it'll work.. Only thing is, the order of keys within the object should be the same... So {a, b, c} and {a, c, b} are treated as different objects even though its basically the same object

|

Abdullah Alkurdi · Accepted Answer · 2019-06-15 16:28:42Z

0

// add the comment's id to the commentsList : 
                        // share.comments.commentsList.addToSet(callback._id);
                        share.update(
                            { '$push': {'comments.commentsList':  mongoose.Types.ObjectId(callback._id) } }
                        , function(){
                            console.log('added comment id to the commentsList array of obectIds')
                        })

answered Jun 15, 2019 at 16:28

Abdullah Alkurdi

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