How to use indexes in aggregate - node.js

Question

I have created the index using the createIndex and then ensure using ensureIndex
db.getCollection('artists').createIndex( { featured : NumberInt(-1), physicalCount : NumberInt(-1),digitalCount : NumberInt(-1),createdAt: NumberInt(-1) } )
db.getCollection('artists').ensureIndex( { featured : NumberInt(-1), physicalCount : NumberInt(-1),digitalCount : NumberInt(-1),createdAt: NumberInt(-1) } )
which create the index :
"8" : {
"v" : 1,
"key" : {
"featured" : -1,
"physicalCount" : -1,
"digitalCount" : -1,
"createdAt" : -1
},
"name" : "featured_-1_physicalCount_-1_digitalCount_-1_createdAt_-1",
"ns" : "global-rockstar.artists"
}
and now I want to use this index in the aggregate query . I know index not work when we use the $project or $group attribute in aggregate . I want to redesign this query so that it can use the indexes but unable to create one
db.getCollection('artists').aggregate([{
$match: query <- initially it is {}
}, {
$project: {
_id: 1,
name: 1,
genres_music: 1,
slug: 1,
country: 1,
featured: 1,
picture: 1,
fans: 1,
fans_a: 1,
credits: 1,
totalPlays: 1,
createdAt: 1,
fanCount: 1,
physicalCount: 1,
digitalCount: 1,
matches: {
$add: [{
$cond: [{
$or: [{
$eq: ['$featured', true]
}, {
$eq: ['$featured', 'on']
}]
},
3, 0
]
}, {
$size: {
$setIntersection: ['$genres_music', usergenres]
}
}]
}
}
}, {
$sort: {
matches: -1,
physicalCount : -1,
digitalCount : -1,
createdAt: -1
}
}, {
$skip: pageSize * page <---- pageSize- 15 , page= 0
}, {
$limit: parseFloat(pageSize)
}])
when I am firing the query like
db.getCollection('artists').find({}).sort({
//"featured" : -1,
"physicalCount" : -1,
"digitalCount" : -1,
"createdAt" : -1
})
this is giving the unexpected result
Please if any one know how to use the aggregate query with indexes for this query please help me out

Answer 1

According to MongoDB documentation:
The $match and $sort pipeline operators can take advantage of an index
when they occur at the beginning of the pipeline.
So If you can, you should put your $sort stage before $project and $group stages.
Placing a $match pipeline stage followed by a $sort stage at the start
of the pipeline is logically equivalent to a single query with a sort
and can use an index. When possible, place $match operators at the
beginning of the pipeline.
In addition, It is preferable to place $skip and $limit stages as early as possible.
Early Filtering
If your aggregation operation requires only a subset
of the data in a collection, use the $match, $limit, and $skip stages
to restrict the documents that enter at the beginning of the pipeline.
When placed at the beginning of a pipeline, $match operations use
suitable indexes to scan only the matching documents in a collection.
And finally,
For a compound index, MongoDB can use the index to support queries on
the index prefixes.