node.js - Mongoose 填充错误模式尚未注册模型。使用 mongoose.model(name, schema)

Question

嗨，他们是我的 Mongoose 模型：

var mongoose = require('mongoose');
var db = require('../../config/db-connect');

var Schema = mongoose.Schema;

var modelSchema = new Schema({
 _id: Number,
 make: String,
 name: String
});

var Model = db.model('Model', modelSchema);

module.exports = Model;

这是另一个：

var mongoose = require('mongoose');
var db = require('../../config/db-connect');

var Schema = mongoose.Schema;

var preferenceSchema = new Schema({
  _id: String,
  list: [{ type: Number, ref: 'Model' }],
});

var Preference = db.model('Preference', preferenceSchema);

module.exports = Preference;

如果我尝试这个查询，它会给我一个错误。

Preference
.findOne()
.where('_id').equals(userId)
.populate('list', '_id make name')
.exec( function(err, result) {

if (err) {
    request.log(['server', 'database', 'error'], 'An error occured during the             execution of the query');
       }

MissingSchemaError：未捕获的错误：尚未为模型“模型”注册架构。使用 mongoose.model(name, schema)