MissingSchemaError：尚未使用moongoose为模型“Post”注册Schema

Question

我收到以下错误MissingSchemaError：尚未为模型“Post”注册Schema。虽然我已经定义了模型。

以下是我使用架构的代码：

var express = require('express');
var router = express.Router();
var mongoose = require( 'mongoose' );
var Post = mongoose.model('Post');
//Used for routes that must be authenticated.
function isAuthenticated (req, res, next) {
    // if user is authenticated in the session, call the next() to call the next request handler 
    // Passport adds this method to request object. A middleware is allowed to add properties to
    // request and response objects

    //allow all get request methods
    if(req.method === "GET"){
        return next();
    }
    if (req.isAuthenticated()){
        return next();
    }

    // if the user is not authenticated then redirect him to the login page
    return res.redirect('/#login');
};

//Register the authentication middleware
router.use('/posts', isAuthenticated);

router.route('/posts')
    //creates a new post
    .post(function(req, res){

        var post = new Post();
        post.text = req.body.text;
        post.created_by = req.body.created_by;
        post.save(function(err, post) {
            if (err){
                return res.send(500, err);
            }
            return res.json(post);
        });
    })
    //gets all posts
    .get(function(req, res){
        console.log('debug1');
        Post.find(function(err, posts){
            console.log('debug2');
            if(err){
                return res.send(500, err);
            }
            return res.send(200,posts);
        });
    });

//post-specific commands. likely won't be used
router.route('/posts/:id')
    //gets specified post
    .get(function(req, res){
        Post.findById(req.params.id, function(err, post){
            if(err)
                res.send(err);
            res.json(post);
        });
    }) 
    //updates specified post
    .put(function(req, res){
        Post.findById(req.params.id, function(err, post){
            if(err)
                res.send(err);

            post.created_by = req.body.created_by;
            post.text = req.body.text;

            post.save(function(err, post){
                if(err)
                    res.send(err);

                res.json(post);
            });
        });
    })
    //deletes the post
    .delete(function(req, res) {
        Post.remove({
            _id: req.params.id
        }, function(err) {
            if (err)
                res.send(err);
            res.json("deleted :(");
        });
    });

module.exports = router;

以下是我定义架构的代码：

var mongoose = require('mongoose');
var Schema = mongoose.Schema;

var postSchema = new mongoose.Schema({
    username: { type: Schema.ObjectId, ref: 'User' },       //should be changed to ObjectId, ref "User"
    created_at: {type: Date, default: Date.now},
    text: String
});

var userSchema = new mongoose.Schema({
    username: String,
    password: String, //hash created from password
    created_at: {type: Date, default: Date.now}
})


mongoose.model('Post', postSchema);
mongoose.model('User', userSchema);

任何人都可以帮助我吗？