类型引用Mongose模式时出错

Question

我正在开发MERN Stack应用程序。类型引用驻留在不同文件中的架构时出现错误。

在profile.js文件中有以下代码：

const express = require("express");
const router = express.Router();
const mongoose = require("mongoose");
const passport = require("passport");

// Load Profile Model
const Profile = require("../../models/Profile");
// Load User Profile
const User = require("../../models/User");

// @route   GET api/profile/test
// @desc    Tests profile route
// @access  Public
router.get("/test", (req, res) => res.json({ msg: "Profile Works" }));

// @route   GET api/profile
// @desc    Get current users profile
// @access  Private
router.get(
  "/",
  passport.authenticate("jwt", { session: false }),
  (req, res) => {
    const errors = {};

    Profile.findOne({ user: req.user.id })
      .then(profile => {
        if (!profile) {
          errors.noprofile = "There is no profile for this user";
          return res.status(404).json(errors);
        }
        res.json(profile);
      })
      .catch(err => res.status(404).json(err));
  }
);

module.exports = router;

运行应用程序时，出现以下错误：

devconnector777\node_modules\mongoose\lib\schema.js:663
    throw new TypeError('Undefined type `' + name + '` at `' + path +
    ^

TypeError: Undefined type `undefined` at `title.required`
  Did you try nesting Schemas? You can only nest using refs or arrays.
    at Function.Schema.interpretAsType (C:\Users\hp-u\Desktop\devconnector777\node_modules\mongoose\lib\schema.js:663:11)
    at Schema.path devconnector777\node_modules\mongoose\lib\schema.js:512:29)
    at Schema.add devconnector777\node_modules\mongoose\lib\schema.js:378:12)
    at Schema.add devconnector777\node_modules\mongoose\lib\schema.js:367:14)
    at new Schema devconnector777\node_modules\mongoose\lib\schema.js:94:10)
    at Function.Schema.interpretAsType devconnector777\node_modules\mongoose\lib\schema.js:616:27)
    at Schema.path devconnector777\node_modules\mongoose\lib\schema.js:512:29)
    at Schema.add devconnector777\node_modules\mongoose\lib\schema.js:378:12)
    at new Schema devconnector777\node_modules\mongoose\lib\schema.js:94:10)
    at Object.<anonymous> devconnector777\models\Profile.js:5:23)
    at Module._compile (module.js:570:32)
    at Object.Module._extensions..js (module.js:579:10)
    at Module.load (module.js:487:32)
    at tryModuleLoad (module.js:446:12)
    at Function.Module._load (module.js:438:3)
    at Module.require (module.js:497:17)
[nodemon] app crashed - waiting for file changes before starting...

我的models文件夹中有2个js文件，即models> User.js和models> Profile.js： 1.User.js：

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

// Create Schema
const UserSchema = new Schema({
  name: {
    type: String,
    required: true
  },
  email: {
    type: String,
    required: true
  },
  password: {
    type: String,
    required: true
  },
  avatar: {
    type: String
  },
  date: {
    type: Date,
    default: Date.now
  }
});

module.exports = User = mongoose.model("users", UserSchema);

2.Profile.js：

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

// Create Schema
const ProfileSchema = new Schema({
  user: {
    type: Schema.Types.ObjectId,
    ref: "users"
  },
  handle: {
    type: String,
    required: true,
    max: 40
  },
  company: {
    type: String
  },
  website: {
    type: String
  },
  location: {
    type: String
  },
  status: {
    type: String,
    require: true
  },
  skills: {
    type: [String],
    require: true
  },
  bio: {
    type: String
  },
  githubusername: {
    type: String
  },
  experience: [
    {
      title: {
        String,
        required: true
      },
      company: {
        type: String,
        required: true
      },
      location: {
        type: String
      },
      from: {
        type: Date,
        required: true
      },
      to: {
        type: Date
      },
      current: {
        type: Boolean,
        default: false
      },
      description: {
        type: String
      }
    }
  ],
  education: [
    {
      school: {
        String,
        required: true
      },
      degree: {
        type: String,
        required: true
      },
      fieldofstudy: {
        type: String,
        required: true
      },
      from: {
        type: Date,
        required: true
      },
      to: {
        type: Date
      },
      current: {
        type: Boolean,
        default: false
      },
      description: {
        type: String
      }
    }
  ],
  social: {
    youtube: {
      type: String
    },
    twitter: {
      type: String
    },
    facebook: {
      type: String
    },
    linkedin: {
      type: String
    },
    instagram: {
      type: String
    }
  },
  date: {
    type: Date,
    default: Date.now
  }
});

module.exports = Profile = mongoose.model("profile", ProfileSchema);

我无法找出错误原因。如何解决此错误？任何帮助将不胜感激。