布尔值到字符串的聚合更改值

Posted 2023-03-29

【中文标题】布尔值到字符串的聚合更改值

【英文标题】：Aggregation change value of a boolean to string

【发布时间】：2020-07-03 20:02:21

【问题描述】：

有一个包含记录的集合，需要将列的布尔值转换为字符串：

[
  
    _id: "bmasndvhjbcw",
    name: "lucas",
    occupation: "scientist",
    passed_phd: true,
    age: 55,
    location: "texas",

  ,
  
    _id: "bmasndvhjbcx",
    name: "mark",
    occupation: "scientist",
    age: 45,
    passed_phd: true,
    location: "texas",

  ,
  
    _id: "bmasndvhjbca",
    name: "stuart",
    occupation: "lab assistant",
    age: 25,
    passed_phd: false,
    location: "texas",

  ,
  
    _id: "bmasndvhjbcq",
    name: "cooper",
    occupation: "physicist",
    age: 69,
    passed_phd: false,
    location: "texas"
  
]

如何将记录的布尔值更改为字符串。

passed_phd 中具有 true(boolean) 的值应转换为 "yes"(string)

passed_phd 中包含 false(boolean) 的值应转换为“no”(string)

[
  
    _id: "bmasndvhjbcw",
    name: "lucas",
    occupation: "scientist",
    passed_phd: "yes",
    age: 55,
    location: "texas",

  ,
  
    _id: "bmasndvhjbcx",
    name: "mark",
    occupation: "scientist",
    age: 45,
    passed_phd: "yes",
    location: "texas",

  ,
  
    _id: "bmasndvhjbca",
    name: "stuart",
    occupation: "lab assistant",
    age: 25,
    passed_phd: "no",
    location: "texas",

  ,
  
    _id: "bmasndvhjbcq",
    name: "cooper",
    occupation: "physicist",
    age: 69,
    passed_phd: "no",
    location: "texas"
  
]

mongodb 4.0 版 .

【参考方案1】：

$cond 聚合管道运算符可以做到这一点。

从 MongoDB 4.2 开始，这些可用于更新或聚合管道，例如：

db.collection.aggregate([
    $set:
            passed_phd:
                        $cond:
                               if:"$passed_phd",
                               then:"yes",
                               else:"no"
                              
                        
   
])

【讨论】：

不，聚合不会更新原始文档。如果您希望在不更改原始输出的情况下修改输出，可以在聚合管道中使用$set 阶段。

我只需要修改输出，不需要更新文档。

$set 对象是一个聚合阶段，您可以将其放入现有管道中。

试过这个'$passed_phd':true,$set:'$passed_phd':"yes"得到这个错误，passed_phd不能以'或$开头

让我们continue this discussion in chat。