如何在 MONGODB WHERE 条件下使用 CASE 语句 [重复]答案

【问题标题】：HOW TO USE CASE STATEMENT IN MONGODB WHERE CONDITION [duplicate]如何在 MONGODB WHERE 条件下使用 CASE 语句 [重复]
【发布时间】：2018-10-23 09:21:10
【问题描述】：

我是 Mongo Db 的新手，希望能在此查询方面提供一些帮助。

 DATA:

       {
            "_id" : ObjectId("5ba2442e9b75ee04d429ed34"),
            "RESOURCE_ID" : "100-101",
            "CITY_ID" : "200-1239",
            "EVENT" : "0"
        },
        {
            "_id" : ObjectId("5ba2442e9b75ee04d429ed34"),
            "RESOURCE_ID" : "100-101",
            "CITY_ID" : "200-1239",
            "EVENT" : "2"
        },
        {
            "_id" : ObjectId("5ba2442e9b75ee04d429ed34"),
            "RESOURCE_ID" : "100-101",
            "CITY_ID" : "200-1239",
            "EVENT" : "3"
        },{
            "_id" : ObjectId("5ba2442e9b75ee04d429ed34"),
            "RESOURCE_ID" : "100-101",
            "CITY_ID" : "800-1239",
            "EVENT" : "1"
        }

我使用 MATCH CONDITION 编写了以下聚合管道 “CITY_ID”：“200-1239”和“RESOURCE_ID”：“100-101”，但是如何在“1”时更改事件，然后是“I”（或）事件，当“2”时，然后是“U”（或）事件时'3' THEN 'D' (OR) 事件当 '0' 然后 'V' 任何人请给我建议。

db.COLLECTION.aggregate([{

{
        $match:{
            $and:[{"CITY_ID" : "200-1239","RESOURCE_ID" : "100-101"}]
        }
    },

 ])

预期输出：

{
            "_id" : ObjectId("5ba2442e9b75ee04d429ed34"),
            "RESOURCE_ID" : "100-101",
            "CITY_ID" : "200-1239",
            "EVENT" : "V"
        },
        {
            "_id" : ObjectId("5ba2442e9b75ee04d429ed34"),
            "RESOURCE_ID" : "100-101",
            "CITY_ID" : "200-1239",
            "EVENT" : "U"
        },
        {
            "_id" : ObjectId("5ba2442e9b75ee04d429ed34"),
            "RESOURCE_ID" : "100-101",
            "CITY_ID" : "200-1239",
            "EVENT" : "D"
        },{
            "_id" : ObjectId("5ba2442e9b75ee04d429ed34"),
            "RESOURCE_ID" : "100-101",
            "CITY_ID" : "200-1239",
            "EVENT" : "I"
        }

【问题讨论】：

标签： mongodb mongoose mongodb-query

【解决方案1】：

你可以在$project中使用$switch

db.COLLECTION.aggregate([

      {
  $match: {
    $and: [{ "CITY_ID": "200-1239", "RESOURCE_ID": "100-101" }]
  }
},

{
  "$project": {
    "RESOURCE_ID": 1,
    "CITY_ID" : 1,
    "EVENT": {
      $switch: {
        branches: [
          { case: { "$eq": ["$EVENT", "1"] }, then: "I" },
          { case: { "$eq": ["$EVENT", "2"] }, then: "U" },
          { case: { "$eq": ["$EVENT", "3"] }, then: "D" },
          { case: { "$eq": ["$EVENT", "0"] }, then: "V" }
        ],
        default: "Z" //You can set default
      }
    }

    }
  } ])

参考链接：https://docs.mongodb.com/manual/reference/operator/aggregation/switch/

【讨论】：

嗨 IftekharDani 我正在尝试此代码一些 trow 错误 Unexpected token ] @ IftekharDani
@Naresh 请检查，我已经更新了我的答案。问题只是缺少括号。
谢谢@IftekharDani 但如何删除默认值
你也可以使用default:"$EVENT"
好的，谢谢@IftekharDani