How to take the latest article for each category in mongodb?

Question

I have next article structure:

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
    }
});

So what I want is to take one latest article sorted by created field for a set of categoryIds. For example I have categories like Cinema, TV, Music, Books, and I want to take latest article for each category. Is it possible to do in one query?

score 1 · Accepted Answer · answered Nov 06 '15 at 07:14

1

First create index for created date and category ids:

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

then take latest article :

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

Maybe there is little syntax error

answered Nov 06 '15 at 07:14

Fariz Aghayev

649
5
17

Uhm, that does not work. If the last X articles were created in category Y, I'd have to know X in order to find the first article of the next category. – Markus W Mahlberg Nov 06 '15 at 09:18
But I need all fields of article to be taken and there are only date and category.id – Eriendel Nov 06 '15 at 10:41
if you want all field add field inside _id: {...} like : http://stackoverflow.com/questions/16662405/mongo-group-query-how-to-keep-fields – Fariz Aghayev Nov 06 '15 at 11:10
Okay, and how to filter by category ids? I mean take last articles of certain categories, not all – Eriendel Nov 06 '15 at 15:17
Using Match . Sir if my answer above good. Plz accept my answer – Fariz Aghayev Nov 06 '15 at 15:30

How to take the latest article for each category in mongodb?

1 Answers1