MongoDB中的条件$ sum [英] Conditional $sum in MongoDB

问题描述

我在mongodb中的集合类似于SQL中的下表:

My collection in mongodb is similar to the following table in SQL:

情感(公司，情感)

现在，我需要执行如下查询:

Now, I need to execute a query like this:

SELECT
  Company, 
  SUM(CASE WHEN Sentiment >0 THEN Sentiment ELSE 0 END) AS SumPosSenti, 
  SUM(CASE WHEN Sentiment <0 THEN Sentiment ELSE 0 END) AS SumNegSenti
FROM Sentiments
GROUP BY Company

我应该怎么做才能在Mongo中编写此查询?我被困在以下查询中:

What should I do to write this query in Mongo? I am stuck at the following query:

db.Sentiments.aggregate(
{ $project: {_id:0, Company:1, Sentiment: 1} },
{ $group: {_id: "$Company", SumPosSenti: {$sum: ? }, SumNegSenti: {$sum: ? } } }
);

推荐答案

如Sammaye所建议，您需要使用

As Sammaye suggested, you need to use the $cond aggregation projection operator to do this:

db.Sentiments.aggregate(
    { $project: {
        _id: 0,
        Company: 1,
        PosSentiment: {$cond: [{$gt: ['$Sentiment', 0]}, '$Sentiment', 0]},
        NegSentiment: {$cond: [{$lt: ['$Sentiment', 0]}, '$Sentiment', 0]}
    }},
    { $group: {
        _id: "$Company",
        SumPosSentiment: {$sum: '$PosSentiment'},
        SumNegSentiment: {$sum: '$NegSentiment'}
    }});

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