我在使用mongoose find（）查询时遇到了问题，我无法解决这个问题。我收到的错误是“TypeError：无法读取undefined”“的属性'find'，我怀疑这是导出/导入问题。如有任何帮助，将不胜感激。
下面是我方案模型文件：

const mongoose = require('mongoose');

const RoleSchema = new mongoose.Schema({
  pageGroup: { 
    type: String, 
    required: true,
  },
  level: { 
    type: String, 
    required: true,
  }
})

const OfficeSchema = new mongoose.Schema({
  officeId: { 
    type: mongoose.Schema.Types.ObjectId, 
    ref: "Office",
    required: true,
  },
  roleId: { 
    type: [mongoose.Schema.Types.ObjectId], 
    required: false,
  },
})

const InstanceSchema = new mongoose.Schema({
  instanceId: { 
    type: mongoose.Schema.Types.ObjectId, 
    ref: "Instance",
    required: true,
  },
  offices: { 
    type: [OfficeSchema], 
    required: false,
  },
})

const UserSchema = new mongoose.Schema({
      firstName: { 
        type: String, 
        required: true 
      },
      lastName: { 
        type: String, 
        required: true 
      },
      email: { 
        type: String, 
        required: false 
      },
      password: { 
        type: String, 
        required: false 
      },
      access: {
        type: [InstanceSchema], 
        required: false,
      }, 
      permissions: {
        type: [RoleSchema], 
        required: false,
      },
      activationToken: {
        type: String,
        required: false,
      },
      roleId: { // new
          type: mongoose.Schema.Types.ObjectId,
          // index: true,
          ref: 'Role',
          // default: null
      },
      employeeId: {
          type: String, 
          required: false 
      },
      instanceId: {
          type: mongoose.Schema.Types.ObjectId, 
          ref: 'Instance', 
          required: true 
      },
      officeId: {
          type: mongoose.Schema.Types.ObjectId, 
          ref: 'Office', 
          required: true 
      }, 
    }, 
    {
      toJSON: { virtuals: true },
      toObject: { virtuals: true },
    })

UserSchema.virtual('instances', {
  ref: 'Instance',
  localField: 'access.instanceId',
  foreignField: '_id',
});

UserSchema.virtual('instances.offices', {
  ref: 'Office',
  localField: 'access.offices.officeId',
  foreignField: '_id',
});

UserSchema.virtual('office', {
  ref: 'Office',
  localField: 'officeId',
  foreignField: '_id',
  justOne: true,
});

UserSchema.virtual('name').get(function() {
  return this.firstName + " " + this.lastName
});

const User = mongoose.model('User', UserSchema);
module.exports = { User }

下面是我的控制器文件中的函数：

const { User } = require('./user.model');

async getEmployees(){
    
    const employees = await User.find({
            instanceId: this._id,
        }, '-password -activationToken -__v -activated')
        .populate('office')
        .sort([['firstName', 1]])
        .exec()

    return employees
},