What is the best way to fetch the most recent article from every category using mongodb?

I am currently working with the following article schema:

var articleSchema=new Schema({
    id : Number,
    title : String,
    sefriendly : String,
    created : Date,
    categories: [
        {
            id: Number,
            name: String,
            sefriendly: String,
            image: String
        }
    ],
    author: {
        id: Number,
        name: String
    }
});

I am looking to retrieve the latest article for each category from a set of categoryIds, sorted by the 'created' field. For example, if my categories include Cinema, TV, Music, and Books, I want to retrieve the latest article for each category. Is it possible to achieve this in a single query?

javascriptmongodbmongooseaggregation-framework

Answer №1

To begin, establish an index for both the created date and category IDs:

db.article.ensureIndex({"created":-1,"categories.id":1})

Next, retrieve the most recent article: 

db.article.aggregate(    [  {$unwind : "$categories"}     { $sort: {"created":-1,"categories.id":1 } },      {        $group:          {            _id: {"categories_id":"$categories.id"},            lastDate: { $last: "$created" }          }      }  ] ,{"allowDiskUse":true})

There may be a small syntax error in the code

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