Mongodb:在组之后的聚合中使用记录计数

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我试图存储输入到管道中的记录总数，以便在以后的计算中使用该数目.如何获取输入数量，然后展开，然后在以后的计算中使用输入数量?

I'm trying to store the total number of records input to the pipe so I can use the number in a later calculation. How do I grab the number of inputs, then unwind, then use the number of inputs later in my calcs?

我可以通过以下方式获取电话号码:

I can get the number by doing this:

db.articles.aggregate([ { $count: "totalArticles" } ]}

我可以通过执行以下操作获得所需的其余数据:

I can get the rest of the data I want by doing this:

db.articles.aggregate([ { $unwind: "$concepts" }, { $group: { _id: "$concepts.text", count: { $sum: 1 }, average: { $avg: "$concepts.relevance" }, } } ])

我真正想做的是:

db.articles.aggregate([ { $count: "totalArticles" }, { $unwind: "$concepts" }, { $group: { _id: "$concepts.text", count: { $sum: 1 }, average: { $avg: "$concepts.relevance" } } }, { $project: { count: "$count", percent: { $divide: [ "$count", "$totalArticles" ] } } }, { $sort: { count: -1 } } ])

推荐答案

您可以使用以下聚合查询.

You can use below aggregation query.

初始$group计算总计数，而$push将概念字段转换为数组字段. $$ROOT访问整个文档.

Initial $group to calculate the total count while $push the concepts field into array field. $$ROOT to access the whole doc.

在下一个$group中保留文章总数.

Retain the total articles count in next $group.

一切都保持原样.

db.articles.aggregate([ {"$group":{ "_id":null, "totalArticles":{"$sum":1}, "concepts":{"$push":"$$ROOT.concepts"} }}, {"$unwind":"$concepts"}, {"$group":{ "_id":"$concepts.text", "totalArticles":{"$first":"$totalArticles"}, "count":{"$sum":1}, "average":{"$avg":"$concepts.relevance"} }}, {"$project":{ "count": "$count", "percent": { "$divide": [ "$count", "$totalArticles" ] } } }, {"$sort": {"count": -1}} ])

$facets也是一种选择，您可以在两个单独的管道中进行两个查询，然后合并以继续其余阶段.

$facets is also an option where you can two queries in two separate pipeline followed by merge to continue with rest of stages.