如何在返回结果中创建新字段并根据使用 Mongoose 的条件在其中设置值？

Posted 2023-03-11

【中文标题】如何在返回结果中创建新字段并根据使用 Mongoose 的条件在其中设置值？

【英文标题】：How can I create new fields in return results and set values in them on the basis of conditions using Mongoose?

【发布时间】：2020-12-10 06:44:52

【问题描述】：

我有一个名为“Animals”的 MongoBD 集合

    [
        
            _id:ObjectId("5f3ecddd7fe1af0c68614605"),
            status: "wild",
            name: "Wolf"
        ,
        
            _id:ObjectId("5f3ecddd7fe1af0c68614606"),
            status: "domestic",
            name: "Dog"
        ,
        
            _id:ObjectId("5f3ecddd7fe1af0c68614607"),
            status: "domestic",
            name: "Pussy Cat"
        ,
        
            _id:ObjectId("5f3ecddd7fe1af0c68614608"),
            status: "wild",
            name: "Lion"
        ,
        
            _id:ObjectId("5f3ecddd7fe1af0c68614609"),
            status: "wild",
            name: "Snake"
        
    ]

我想在 mongoose 中使用聚合管道查询该集合，并使用一个新字段返回结果，该字段根据文档中的 status 字段对它们进行分类。例如，具有status: "wild" 的文档获取新字段new_field: "Tough Forest Animal"

然后有status: "domestic"的文档得到新字段new_field: "Friendly Neighborhood Animal"

我想要这样的结果

[
    
        _id: "5f3ecddd7fe1af0c68614605",
        status: "wild",
        name: "Wolf",
        new_field: "Tough Forest Animal"
    ,
    
        _id: "5f3ecddd7fe1af0c68614606",
        status: "domestic",
        name: "Dog",
        new_field: "Friendly Neighborhood Animal"
    ,
    
        _id: "5f3ecddd7fe1af0c68614607",
        status: "domestic",
        name: "Pussy Cat",
        new_field: "Friendly Neighborhood Animal"
    ,
    
        _id: "5f3ecddd7fe1af0c68614608",
        status: "wild",
        name: "Lion",
        new_field: "Tough Forest Animal"
    ,
    
        _id: "5f3ecddd7fe1af0c68614609",
        status: "wild",
        name: "Snake",
        new_field: "Tough Forest Animal"
    
]

非常感谢给予我的所有帮助。谢谢

【参考方案1】：

我终于弄明白了。使用 switch 语句

AnimalsModel.aggregate([
    
        $project: 

            "_id": 1,
            "status": 1,
            "name": 1,
            "new_field": 
                "$switch": 
                    "branches": [
                         "case":  "$eq": [ "$status", "wild" ] , "then": 'Tough Forest Animal' ,
                         "case":  "$eq": [ "$status", "domestic" ] , "then": 'Friendly Neighborhood Animal' ,
                    ],
                    "default": 'None of the above'
                
            
        
    
],function (error, animals) 
    console.log(animals)
);