问从nodejs服务器中mongo文档内的子数组中删除项

EN

node:events:353
      throw er; // Unhandled 'error' event
      ^
TypeError: user.pull is not a function

const deleteMessage = (userID) => {

  console.log('userID delete : ' +userID)
  //Delete message collection corresponding to the userID
  Message.findByIdAndDelete({_id:userID}).catch((err) => { console.log(err.message);});

    //Delete messages corresponding to the userID from the receiver' message list
  Message.find({users:{$elemMatch:{ _id:userID}}}, (err,doc)=>{
    console.log(doc);

    doc.forEach((user)=> {

      user.pull({_id:userID})
      doc.save();
    })
    
  }).catch((err) => {
    console.log(err.message);
  });
}

const mongoose = require("mongoose");
const Schema = mongoose.Schema;

const contentSchema = new Schema(
  {
    isMy: Boolean,
    message: String,
    createdAt: Date,
  }
);

const receiverSchema = new Schema({
  _id: String,
  messages: [contentSchema],
});

const messageSchema = new Schema({
  _id: String,
  users: [receiverSchema],
});

module.exports = mongoose.model("Message", messageSchema);