对于某些字段为{ wins: Number }的集合,我如何使用 MongoDB Aggregation Framework 获取集合中所有文档的获胜总数?
For some collection with a field { wins: Number }, how could I use MongoDB Aggregation Framework to get the total number of wins across all documents in a collection?
如果我有3个文档分别为wins: 5,wins: 8和wins: 12,如何使用MongoDB Aggregation Framework返回总数,即total: 25.
If I have 3 documents with wins: 5, wins: 8, wins: 12 respectively, how could I use MongoDB Aggregation Framework to return the total number, i.e. total: 25.
推荐答案总和
要使用MongoDB的聚合框架时获取分组字段的总和,您需要使用$group和$sum:
db.characters.aggregate([ { $group: { _id: null, total: { $sum: "$wins" } } } ] )在这种情况下,如果要获取所有wins的总和,则需要使用$语法以$wins的形式引用字段名称,该语法仅获取wins的值分组文档中的字段,并将它们汇总在一起.
In this case, if you want to get the sum of all of the wins, you need to refer to the field name using the $ syntax as $wins which just fetches the values of the wins field from the grouped documents and sums them together.
您也可以通过传递特定值(如您在注释中所做的那样)来sum其他值.如果您有
You can sum other values as well by passing in a specific value (as you'd done in your comment). If you had
{ "$sum" : 1 },
实际上是所有wins的计数,而不是总数.
that would actually be a count of all of the wins, rather than a total.
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