MongoDB How to sort an array of objects without using aggregate & group?

Question

I want to sort an array of objects inside my modal and the only way to do it (as I saw) is the following:

...
const notifications = await Notification
            .aggregate([
                {$match: {to: userId}},
                {$unwind: '$messages'},
                {$sort: {'messages.createdAt':-1}},
                {$group: {
                        _id: '$_id',
                        createdAt: {$first: '$createdAt'},
                        messages: {$push: '$messages'},
                    }}
            ])
...

However, I am wondering if there is another way to do it. It seems that I have to do so many operations, even though all I want is to sort an array (grouping for example would make sense if I would actually change anything about the data but I dont). The only other way to do it I found was this:

const notifications = await Notification.findOne({to: userId}).sort({'messages.createdAt': -1})

but that doesnt sort my array in descending order, basically does nothing.

const notificationSchema = new mongoose.Schema({
    to: {
        type: mongoose.Schema.Types.ObjectId,
        ref: 'User'
    },
    messages: [{
        title: {
            type: String,
            required: true
        },
        body: {
            type: String
        },
        isRead: {
            type: Boolean,
            default: false
        },
        createdAt: {
            type: Date,
            default: new Date()
        }
    }, ]
},{timestamps: true});

Charchit Kapoor · Accepted Answer · 2022-11-02 11:06:26Z

2

You can use $sortArray operator if you have MongoDB 5.2 or above. Otherwise, you can go through the path of unwinding and grouping. Or you can modify your update operation for the Notification model so that it already sorts, the messages by their createdAt, in descending order and you don't have to perform the sorting while fetching the notification using find method. Something like this:

db.collection.update({
  "notification": "Hello"
},
{
  "$push": {
    messages: {
      "$each": [
        {
          id: "4"
        }
      ],
      "$sort": {
        id: -1
      }
    }
  }
})

Playground link.

answered Nov 2, 2022 at 11:06

Charchit Kapoor

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6 Comments

user6377312 Over a year ago

Thank you so much. How can I use it in my case - please see my link to same playground: mongoplayground.net/p/xujp_G7_rLV

Charchit Kapoor Over a year ago

Playground doesn't support all the update methods. I have updated your playground to make it work. Check this mongoplayground.net/p/UfOaJTZL-tO. @juliascoding

user6377312 Over a year ago

thanks, but how can I use each sort and still push my message (object) into the messages array? mongoplayground.net/p/_tbJP4Vh6XP

Charchit Kapoor Over a year ago

You should provide the message in $each array like this mongoplayground.net/p/ImXj_1XQCWH

Charchit Kapoor Over a year ago

Not as such, in fact it's efficient since sorting while saving, prevents sorting again and again, while fetching.

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