在 MongoDB 中聚合不同的值 [英] Aggregate distinct values in MongoDB
问题描述
我有一个包含 18625 个集合的 mongodb 数据库.它有以下键:
I have a mongodb db with 18625 collections. It has following keys:
"_id" : ObjectId("5aab14d2fc08b46adb79d99c"),
"game_id" : NumberInt(4),
"score_phrase" : "Great",
"title" : "NHL 13",
"url" : "/games/nhl-13/ps3-128181",
"platform" : "PlayStation 3",
"score" : 8.5,
"genre" : "Sports",
"editors_choice" : "N",
"release_year" : NumberInt(2012),
"release_month" : NumberInt(9),
"release_day" : NumberInt(11)
现在,我希望创建仅包含流派的另一个维度/集合.
Now, i wish to create another dimension/ collection with only genres.
如果我使用以下查询:
db.ign.aggregate([ {$project: {"genre":1}}, { $out: "dimen_genre" } ]);
它生成了 18625 个集合,即使只有 113 个不同的集合类型.
It generates 18625 collections, even though there are only 113 distinct genres.
如何在此处应用 distinct 并获取仅具有不同 113 个值的流派的集合.我用谷歌搜索,它表明聚合和不同在 mongo 中不能一起工作.我也试过:db.dimen_genre.distinct('genre').length这表明在维度_流派中,有 113 个不同的流派.
How to apply distinct here and get the collection for genres with only the distinct 113 values. I googled, bt it showed that aggregate and distinct don't work together in mongo. I also tried : db.dimen_genre.distinct('genre').length this showed that in dimension_genre, there are 113 distinct genres.
确切地说,如何从只有不同值的现有集合中创建集合.
Precisely, how to make a collection from existing one with only distinct values.
我对 NoSQL 非常陌生.
I am really new to NoSQLs.
推荐答案
您可以使用 $addToSet 将唯一值分组到一个文档中,然后 $unwind 取回多个文档:
You can use $addToSet to group unique values in one document and then $unwind to get back multiple docs:
db.ign.aggregate([
{
$group: {
_id: null,
genre: { $addToSet: "$genre" }
}
},
{
$unwind: "$genre"
},
{
$project: {
_id: 0
}
},
{ $out: "dimen_genre" }
]);
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