mongodb -如何在聚合查询中写入条件

Question

我对Mongo非常陌生，我有一个关于有条件计算的聚合查询的问题：

我有一个评论集，每个文档包含一个情感评分。我想：

1)按项目分列的小组审查

2)在该项目的所有评论中，获取每个项目的平均情绪得分，并按此排序。

3)获取每个项目组的评论总数

4)获得每个项目的积极情绪评价总数(例如，情绪得分>75的#评价)。

5)获得每一项负面情绪评价的总数(例如，情绪得分<75的#评价)

到目前为止，我有下面的查询，它涉及1-3，但也不确定如何获得4/5：

db.reviews.aggregate( 
    {"$group" : 
        {_id: "$item", 
        sentiment: {$avg : "$sentimentScore"}, 
        count: {$sum: 1 } 
        } 
    }, 
    {"$sort": { sentiment: -1 } } 
)

Answer 1

我假设您希望在给定阈值(即count和negative - <75 )的情况下，为sentiment有单独的负值和正值字段，即积极情绪的总#、消极情绪的总#以及总情感。

db.sentiments.aggregate([
    {"$group" : 
        {_id: "$item", 
        sentiment: {$avg : "$sentiment_score"}, 
        postiive_sentiments: {$sum: { $cond: { if: { $gt: [ "$sentiment_score", 75 ] }, then: 1, else: 0 } }},
        negative_sentiments: {$sum: { $cond: { if: { $lt: [ "$sentiment_score", 75 ] }, then: 1, else: 0 } }},
        count: {$sum: 1 } 
        } 
    },
     {"$sort": { sentiment: -1 } } 
])

样本数据：

{ "_id" : ObjectId("5991329ea37dbc24842a68be"), "item" : "test1", "sentiment_score" : 50 }
{ "_id" : ObjectId("599132a2a37dbc24842a68bf"), "item" : "test1", "sentiment_score" : 40 }
{ "_id" : ObjectId("599132a4a37dbc24842a68c0"), "item" : "test1", "sentiment_score" : 80 }
{ "_id" : ObjectId("599132aba37dbc24842a68c1"), "item" : "test2", "sentiment_score" : 80 }
{ "_id" : ObjectId("599132ada37dbc24842a68c2"), "item" : "test2", "sentiment_score" : 30 }
{ "_id" : ObjectId("599132b0a37dbc24842a68c3"), "item" : "test2", "sentiment_score" : 38 }
{ "_id" : ObjectId("599132b6a37dbc24842a68c4"), "item" : "test3", "sentiment_score" : 78 }
{ "_id" : ObjectId("599132b9a37dbc24842a68c5"), "item" : "test3", "sentiment_score" : 88 }
{ "_id" : ObjectId("599132bba37dbc24842a68c6"), "item" : "test3", "sentiment_score" : 58 }
{ "_id" : ObjectId("599132c4a37dbc24842a68c7"), "item" : "test3", "sentiment_score" : 98 }
{ "_id" : ObjectId("599132cba37dbc24842a68c8"), "item" : "test4", "sentiment_score" : 65 }
{ "_id" : ObjectId("599132d2a37dbc24842a68c9"), "item" : "test4", "sentiment_score" : 30 }
{ "_id" : ObjectId("599132d6a37dbc24842a68ca"), "item" : "test4", "sentiment_score" : 10 }

//结果：

{ "_id" : "test3", "sentiment" : 80.5, "negative_sentiments" : 3, "positive_sentiments" : 1, "count" : 4 }
{ "_id" : "test1", "sentiment" : 56.666666666666664, "negative_sentiments" : 1, "positive_sentiments" : 2, "count" : 3 }
{ "_id" : "test2", "sentiment" : 49.333333333333336, "negative_sentiments" : 1, "positive_sentiments" : 2, "count" : 3 }
{ "_id" : "test4", "sentiment" : 35, "negative_sentiments" : 0, "positive_sentiments" : 3, "count" : 3 }