MongoDB聚合-如果数组中的值匹配 [英] MongoDB Aggregation - match if value in array

问题描述

我有一个要对其进行汇总的集合，基本上已经将其归结为

I have a collection that I'm performing an aggregation on and I've basically gotten it down to

{array:[1,2,3], value: 1},
{array:[1,2,3], value: 4}

我将如何执行聚合匹配以检查该值是否在数组中?我尝试使用{$match: {"array: {$in: ["$value"]}}}，但找不到任何东西.

How would I perform an aggregation match to check if the value is in the array? I tried using {$match: {"array: {$in: ["$value"]}}} but it doesn't find anything.

我希望输出(如果以上面的示例为例)为

I would want the output (if using the above as an example) to be:

{array:[1,2,3], value:1}

推荐答案

基于@chridam的回答略有不同:

A slight variation based on @chridam's answer:

db.test.aggregate([
    { "$unwind": "$array" },
    { "$group": {
                  _id: { "_id": "$_id", "value": "$value" },
                  array: { $push: "$array" },
                  mcount: { $sum: {$cond: [{$eq: ["$value","$array"]},1,0]}}
                }
    },
    { $match: {mcount: {$gt: 0}}},
    { "$project": { "value": "$_id.value", "array": 1, "_id": 0 }}
])

想法是$unwind和$group返回数组，并在mcount中计算与该值匹配的项目数.之后，在mcount > 0上使用简单的$match即可过滤掉不需要的文档.

The idea is to $unwind and $group back the array, counting in mcount the number of items matching the value. After that, a simple $match on mcount > 0 will filter out unwanted documents.

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