MongoDB更新JSON对象数组报错：qualifications字段类型不符排查

问题背景 #

数据Schema定义如下：

qualifications:[ {
    Experience: [{
      title: String,
      companyName: String,
      location: String,
      years: Number
    }],
    Education:[ {
      school: String,
      years: Number,
    }],
    Licences: [String],
    Honnors: [String],
  }],

需求是向Education数组中添加新对象，尝试了以下添加代码：

const updateEducation = async (req, res) => {
  try {
    const user = await User.findOneAndUpdate(
      { _id: req.body.userid },
      {
        $push: {
            
            qualifications:{
              Education: {
                school: req.body.educationSchool,
                years: req.body.educationYearText
              }
            }
          
        },
      },
      { new: true }
    );

删除代码如下：

const deleteEducation = async (req, res) => {
  try {
    const user = await User.findOneAndUpdate(
      { _id: req.body.userid },
      {
        $pull: {
          "qualifications.Education": {
            school: req.body.school
          }
        },
      }
    );

但添加时出现错误：

"error": "Plan executor error during findAndModify :: caused by :: The field 'qualifications' must be an array but is of type object in document"

问题原因 #

报错核心是qualifications是数组类型，但你用$push直接给它赋值一个对象，这会把整个数组覆盖成单个对象，违反了原本的Schema类型定义，所以MongoDB抛出类型错误。

另外不管是添加还是删除操作，都没正确定位到qualifications数组内部元素的Education子数组——因为qualifications本身是数组，里面只有一个对象元素，必须先定位到这个数组元素，才能操作它的Education子数组。

正确解法 #

1. 向Education数组添加对象 #

需要用数组索引（比如0，因为你的qualifications数组只有一个元素）或者$定位符来指定要操作的qualifications元素，然后对其下的Education数组执行$push：

const updateEducation = async (req, res) => {
  try {
    const user = await User.findOneAndUpdate(
      { _id: req.body.userid },
      {
        $push: {
          // 用0索引定位qualifications数组的第一个（也是唯一）元素
          "qualifications.0.Education": {
            school: req.body.educationSchool,
            years: parseInt(req.body.educationYearText) // 注意转成Number类型，匹配Schema
          }
        }
      },
      { new: true }
    );
    res.status(200).json(user);
  } catch (err) {
    res.status(500).json({ error: err.message });
  }
};

如果未来qualifications数组可能有多个元素，且需要匹配特定条件的元素，可以用$定位符（前提是查询条件能匹配到qualifications里的目标元素）：

// 假设要匹配qualifications中某个条件的元素，比如有特定Experience的元素
const user = await User.findOneAndUpdate(
  { 
    _id: req.body.userid,
    "qualifications.Experience.title": "目标职位" // 匹配qualifications数组中的元素
  },
  {
    $push: {
      "qualifications.$.Education": { // $代表查询条件匹配到的qualifications元素索引
        school: req.body.educationSchool,
        years: parseInt(req.body.educationYearText)
      }
    }
  },
  { new: true }
);

2. 删除Education数组中的对象 #

同理，需要定位到qualifications数组元素下的Education数组，执行$pull：

const deleteEducation = async (req, res) => {
  try {
    const user = await User.findOneAndUpdate(
      { _id: req.body.userid },
      {
        $pull: {
          "qualifications.0.Education": {
            school: req.body.school
          }
        }
      },
      { new: true } // 加上这个选项返回更新后的文档，方便验证
    );
    res.status(200).json(user);
  } catch (err) {
    res.status(500).json({ error: err.message });
  }
};

内容的提问来源于stack exchange，提问作者facosob