保存Data Express / Mongoose时引用其他模型

Question

I have a simple express app where users can log in and post pictures of mountains. I'm having an issue saving the posts the users add. Specifically, the user id that is referenced from another schema(user schema). When I submit the form, I get an undefined error on the "._id" and I'm not sure how to go about fixing it.

Below are my model schemas.

const userSchema = new Schema({
    name: String,
    email: String,
    username: String,
    password: String,
});



const canyonSchema = new Schema({
     canyon: String,
   image: String,
   description: String,
   cost: Number,
   createdAt: { type: Date, default: Date.now },
   author: {
      id: {
         type: mongoose.Schema.Types.ObjectId,
         ref: "User"
      },
      username: String
   }
});
const Canyon = mongoose.model("Canyon", canyonSchema);
module.exports = Canyon;

const  User = mongoose.model('User', userSchema);
module.exports = User 

Here is the logic that is supposed to save the information to mongo. When I run, I get a "._id undefined". Any help.

    const User = require('../models/user');
    const Canyon = require('../models/Canyon');

    router.post("/add", , function(req, res){

     if(req.body.canyon &&
        rea.body.image &&
        req.body.description){

        const newCanyon = {
            canyon: req.body.canyon,
            image: req.body.image,
            description: req.body.description,
            author: {
                id: req.user._id,
            }, username: req.user.username
          };

          Canyon.create(newCanyon, function(error, canyon){
            if(error){
                return next(error)
            } else {
                req.session.userId = user._id;
                return res.redirect('/profile')
            }
          });
     } else {
        const err = new Error('All fields required.');
          err.status = 400;
          return next(err);
     }

      });

Answer 1

In your model schema, instead of

const canyonSchema = new Schema({
 canyon: String,
 image: String,
 description: String,
 cost: Number,
 createdAt: { type: Date, default: Date.now },
 author: {
  id: {
     type: mongoose.Schema.Types.ObjectId,
     ref: "User"
  },
  username: String
  }
});

Make the author itself the reference:

const canyonSchema = new Schema({
 canyon: String,
 image: String,
 description: String,
 cost: Number,
 createdAt: { type: Date, default: Date.now },
 author: { type: mongoose.Schema.ObjectId, ref: 'User', index: true },
 });

To create a canyon object,

const newCanyon = {
        canyon: req.body.canyon,
        image: req.body.image,
        description: req.body.description,
        author: req.user._id
      };

To get the user information embedded in the canyon object when query on canyons, just populate the author in the query,

Canyon.findById(id).populate('author').exec()