What is the best way to arrange an array based on a specific field within a MongoDB document?

Question

What is the best way to arrange an array based on a specific field within a MongoDB document?

In my question document, I have a schema named QuestionSchema that includes fields such as title, body, user, category, comments, tags, image, and createdAt.

var QuestionSchema = new Schema({
    title: {
        type: String,
        default: '',
        trim: true
    },
    body: {
        type: String,
        default: '',
        trim: true
    },
    user: {
        type: Schema.ObjectId,
        ref: 'User'
    },
    category: [],
    comments: [{
        body: {
            type: String,
            default: ''
        },
        root: {
            type: String,
            default: ''
        },
        user: {
            type: Schema.Types.ObjectId,
            ref: 'User'
        },
        createdAt: {
            type: Date,
            default: Date.now
        }
    }],
    tags: {
        type: [],
        get: getTags,
        set: setTags
    },
    image: {
        cdnUri: String,
        files: []
    },
    createdAt: {
        type: Date,
        default: Date.now
    }
});

I am facing an issue where I need to sort the comments array by the root field. I attempted to manually sort the array at the backend and also tried using aggregation but was unsuccessful in sorting it. Can someone please provide assistance?

javascript mongodb mongoose mongodb-query

Answer 1

Answer №1

If you have a model object called Question in your code and you want to sort the "comments by "date" from createdAt, you can achieve this using the .aggregate() method:

Question.aggregate([
    { "$match": { "_id": docId } }, 
     { "$unwind": "comments" },
     { "$sort": { "_id": 1, "comments.createdAt": 1 } },
     { "$group": {
         "_id": "$_id",
         "title": { "$first": "$title" },
         "body": { "$first": "$body" },
         "user": { "$first": "$user" },
         "comments": { "$push": "$comments" },
         "tags": { "$first": "$tags" },
         "image": { "$first": "$image" },
         "createdAt": { "$first": "$createdAt" }
     }}],
 function(err,results) {
     // handle sorted results here
 });

However, if you don't need to aggregate across documents, it's simpler to just use JavaScript methods like .sort():

Quesion.findOneById(docId,function(err,doc) {
     if (err) throw (err);
     var mydoc = doc.toObject();
     mydoc.questions = mydoc.questions.sort(function(a,b) {
         return a.createdAt > b.createdAt;
     });
    console.log( JSON.stringify( doc, undefined, 2 ) ); // Nicely formatted output
});

In conclusion, while MongoDB provides tools for server-side sorting, it's often more efficient to do this on the client side when retrieving data unless aggregation across documents is necessary.

Both examples have been provided for reference.

Answer 2

If you have a model object called Question in your code and you want to sort the "comments by "date" from createdAt, you can achieve this using the .aggregate() method:

Question.aggregate([
    { "$match": { "_id": docId } }, 
     { "$unwind": "comments" },
     { "$sort": { "_id": 1, "comments.createdAt": 1 } },
     { "$group": {
         "_id": "$_id",
         "title": { "$first": "$title" },
         "body": { "$first": "$body" },
         "user": { "$first": "$user" },
         "comments": { "$push": "$comments" },
         "tags": { "$first": "$tags" },
         "image": { "$first": "$image" },
         "createdAt": { "$first": "$createdAt" }
     }}],
 function(err,results) {
     // handle sorted results here
 });

However, if you don't need to aggregate across documents, it's simpler to just use JavaScript methods like .sort():

Quesion.findOneById(docId,function(err,doc) {
     if (err) throw (err);
     var mydoc = doc.toObject();
     mydoc.questions = mydoc.questions.sort(function(a,b) {
         return a.createdAt > b.createdAt;
     });
    console.log( JSON.stringify( doc, undefined, 2 ) ); // Nicely formatted output
});

In conclusion, while MongoDB provides tools for server-side sorting, it's often more efficient to do this on the client side when retrieving data unless aggregation across documents is necessary.

Both examples have been provided for reference.

What is the best way to arrange an array based on a specific field within a MongoDB document?

Answer №1

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