mongo.Aggregate.倚天剑.横扫千军

2020-05-22 00:00:00 示例语法图标白骨九阴

练功贵在坚持，凡在武学上面有很高造诣的，不外乎俩种人，一种天赋极高的，看一遍就会，达到武功精要，另外一种的就是勤奋的，假已时日，也能登峰造极，大多数人属于后者，气沉丹田，让我们一起来修行。。。

九阴白骨爪之$addFields

简介：在文档中添加新的字段

语法：{ $addFields: { <newField>: <expression>, ... } }

支持版本： 3.4

示例：
数据源：
{
  _id: 1,
  student: "Maya",
  homework: [ 10, 5, 10 ],
  quiz: [ 10, 8 ],
  extraCredit: 
}
{
  _id: 2,
  student: "Ryan",
  homework: [ 5, 6, 5 ],
  quiz: [ 8, 8 ],
  extraCredit: 8
}
查询语句
db.scores.aggregate( [
   {
     $addFields: {
       totalHomework: { $sum: "$homework" } ,
       totalQuiz: { $sum: "$quiz" }
     }
   },
   {
     $addFields: { totalScore:
       { $add: [ "$totalHomework", "$totalQuiz", "$extraCredit" ] } }
   }
] )
输出结果
{
  "_id" : 1,
  "student" : "Maya",
  "homework" : [ 10, 5, 10 ],
  "quiz" : [ 10, 8 ],
  "extraCredit" : ,
  "totalHomework" : 25,
  "totalQuiz" : 18,
  "totalScore" : 43
}
{
  "_id" : 2,
  "student" : "Ryan",
  "homework" : [ 5, 6, 5 ],
  "quiz" : [ 8, 8 ],
  "extraCredit" : 8,
  "totalHomework" : 16,
  "totalQuiz" : 16,
  "totalScore" : 40
}

相关文章