node.js - 如何使用聚合索引

Question

我已经使用createIndex创建了索引，然后使用ensureIndex确保

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) } )

创建索引:

"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"
}

现在我想在聚合查询中使用这个索引。我知道当我们在聚合中使用 $project 或 $group 属性时索引不起作用。我想重新设计这个查询，以便它可以使用索引但无法创建索引

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)
            }])

当我像这样触发查询时

db.getCollection('artists').find({}).sort({
        //"featured" : -1,
        "physicalCount" : -1,
        "digitalCount" : -1,
        "createdAt" : -1
    })

这给出了意想不到的结果

如果有人知道如何使用带有此查询索引的聚合查询，请帮助我

Answer 1

根据 MongoDB 文档:

The $match and $sort pipeline operators can take advantage of an index when they occur at the beginning of the pipeline.

因此，如果可以的话，您应该将 $sort 阶段放在 $project 和 $group 阶段之前。

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.

此外，最好尽早放置 $skip 和 $limit 阶段。

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.

最后，

For a compound index, MongoDB can use the index to support queries on the index prefixes.