汇总Mongo子文档数组 [英] Summing Mongo Sub-Document Array
本文介绍了汇总Mongo子文档数组的处理方法,对大家解决问题具有一定的参考价值,需要的朋友们下面随着小编来一起学习吧!
问题描述
db.test3.find()
{ "_id" : 1, "results" : [{"result" : {"cost" : [ { "priceAmt" : 100 } ] } } ] }
我未成功尝试以下操作:
I tried the following unsucessfully:
db.test3.aggregate({$group : {_id: "", total : {$sum:
$results.result.cost.priceAmt"}}}, {$project: {_id: 0, total: 1}})
{ "result" : [ { "total" : 0 } ], "ok" : 1 }
编辑
所需的输出:
100 // sum of each "priceAmt"
推荐答案
您必须使用$unwind
运算符将数组项转换为单个文档.
You'll have to use the $unwind
operator to turn array items into individual documents.
db.test3.aggregate({$unwind: "$results"}, {$unwind: "$results.result.cost"}, {$group : {_id: "", total : {$sum: "$results.result.cost.priceAmt"}}}, {$project: {_id: 0, total: 1}})
$unwind
需要应用两次,因为您有一个嵌套数组.
The $unwind
needs to be applied twice because you have a nested array.
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