MongoDB - 聚合

 1 # 输出文档中除了web_name和click_num外，还包含默认的 _id 域
 2 db.test_study.aggregate([
 3     {
 4         $project: {
 5             web_name: "$web_name",
 6             click_num: "$click_num"
 7         }
 8     }
 9 ])
10 
11 
12 # 设置 _id:0 输出文档中只包括 web_name 和 click_num，不包含 _id 域
13 db.test_study.aggregate([
14     {
15         $project: {
16          _id:0,
17             web_name: "$web_name",
18             click_num: "$click_num"
19         }
20     }
21 ])

# 事例数据
{
    "_id": 1,
    "title": "789",
    "author": {
        "last": "Li",
        "first": "Lucy",
        "country": "China"
    },
    "copies": 5,
    "lastModified": "2019-07-28"
}

db.test.aggregate([{
    $project: {
    _id:0,
        title: "$title",
        author_country: "$author.country"
    }
}])

db.test.aggregate([{
    $project: {
        "_id":0,
        "copies": 0,
        "author.country": 0
    }
}])

注意：

"copies" 要加双引号

MongoDB - 聚合

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