如何将MongooseMap转换为JSON对象以将其从Node js发送到React？

Question

In mongoose, there is Map data type that allows to store arbitrary keys. I understand that to get and set values I should use get and set methods. However, when I send an object to frontend, Nodejs sends just empty JSON object. Is there a way to automatically convert Mongoose object, that has Map type, into JSON object to send over the network, without extracting every key with get on the backend?

My model:

var  mongoose = require('mongoose');

var User = require('./user');
var Post = require('./post');
const Schema = mongoose.Schema;
const ObjectId = mongoose.Schema.Types.ObjectId;

const DescriptionSchema = new Schema({
    timeStamp: {type: Date, default: Date.now},
    postid: {type: ObjectId, ref: 'Post'},
    userid: {type: ObjectId, ref: 'User'},
    dstrings:{
        type: Map,
        of: String// key value
      }
});

module.exports = mongoose.model('Description', DescriptionSchema);

My controller:

// '/v1/description/add'
    api.post('/add', authenticate,(req, res) => {
        let description = new Description({         
            postid: ObjectId(req.body.postid),
            userid: ObjectId(req.user.id), 
            dstrings:req.body.dstrings,

        });
        description.save(function(err, description) {
            if (err) {
                res.status(500).json({ message: err });
            } else {
//  description.dstrings is equal to {} on the frontend               
                    res.status(200).json( description );
                }
            });  
        });

JSON.stringify didn't work; I checked database, it has the value.

Answer 1

There is nothing wrong with the .json() Syntax But with arguments of the .save() callback function

The save function's callback will accept the following arguments :

• The error
• The document that was saved

Please read the mongoose Prototype.save() docs

The link is here

Answer 2

Found the answer here . The problem was in serialization. To serialize an object that contains Map we can pass a function as the second argument to JSON.stringify as described in the link above. Then we can deserialize on frontend by passing another function to JSON.parse .