Mongo Aggregation

I have following documents in my collection { '_id': ObjectId('54490b8104f7142f22ecc97f'), 'title': 'Sample1', 'slug': 'samplenews', 'cat': 'sports',

Solution 1:

Assuming you have the latest version of mongodb installed, one way of doing it is:

• Sort the records based on the published_date in descending order.
• group the records based on their category. For each group, collect all the records together in an array.
• In the javascript/client side code, slice the top 5 records, of each group(category).

The $slice is not available in the server side $project aggregation pipeline operator, which holds us from performing the operation on the server side.

var result = db.collection.aggregate(
[
{$sort:{"published_date":-1}},
{$group:{"_id":"$category","values":{$push:"$$ROOT"}}}
]
).map(function(doc){
return {"category":doc._id,"records":doc.values.slice(0,5)};
});

The result variable will now be an array of documents. Each document representing each category and in turn having an array of top 5 records.

Solution 2:

You can sort and then limit your request.

$top_five_other = iterator_to_array($db->find(array('category'=>'other')->sort(array('published_date'=>-1))->limit(5));

Solution 3:

you can try aggregate query

1-db.collection.aggregate({ $group : { _id : { category:"$category"}, total : { $sum : 1 }}},{$sort:{_id:1}})

OR

db.collection.aggregate({ $group : { _id : { category:"$category"}, total : { $sum : 1 }}},{$sort:{_id:1}})..forEach( function(myDoc) { print(myDoc._id.category);

})