如何在 MongoDB 聚合管道中将对象/子文档数组转换为字符串数组？

问题描述

我有以下结构的文档

{
    "_id":{"$oid":"..."},"work_type": "ASSIGNMENT","materials": [
        {
        "driveFile": {
            "driveFile": {
                "id": "...","title": "filename","alternateLink": "https://drive.google.com/...","thumbnailUrl": "https://drive.google.com/..."
            },"shareMode": "STUDENT_copY"
        }
        },{
        "youtubeVideo": {
            "id": "tfdbq","alternateLink": "https://www.youtube.com/watch?v=..."
            }
        }
    ]
}

并且我想将数组中的对象转换为 JSON 字符串，以便我可以将材料字段作为 sql 中的重复字符串列导入

结果：

{
    "_id":{"$oid":"..."},"materials": [
        "{\"driveFile\":{\"driveFile\":{\"id\":\"...\",\"title\":\"filename\",\"alternateLink\":\"https://drive.google.com/...\",\"thumbnailUrl\":\"https://drive.google.com/...\"},\"shareMode\":\"copY"}}","{\"youtubeVideo\":{\"id\":\"tfdbq\",\"alternateLink\":\"https://www.youtube.com/watch?v=...\"}}""
    ]
}

解决方法

我不确定是否有任何简单的选项可以做到这一点，您可以尝试从 MongoDB v4.4 开始的 $function 运算符，间接它是 JavaScript 代码，

• 使用 aggregate()

  {
    $set: {
      materials: {
        $function: {
          body: function(materials) { 
            let m = []; 
            for (let i = 0; i < materials.length; i++) 
              m.push(JSON.stringify(materials[i])); 
            return m; 
          },args: ["$materials"],lang: "js"
        }
      }
    }
  }

Playground

• 从 MongoDB v4.2 开始使用 update with aggregation pipeline

Playground