Mongoose nested schema

Question

I want to make a system of topics. each topic may have subtopics which are also topics. meaning the subtopics may also have subtopics. for example example image

I tried to create a topic schema and add a subtopic field which will ref to topic schema too. cant seem to get this working my schema code:

const mongoose = require('mongoose');

const TopicSchema = new mongoose.Schema({
    name: {type:String,unique:true},
    sub_topic:[{type:mongoose.Schema.Types.ObjectId, ref : 'Topic'}] 
});

const Topic =mongoose.model('Topic', TopicSchema);
module.exports = Topic;

Also what the data im sending to the server should look like to make a new instance? and on the server how do i save it?

i try to save like this now : const topic = new Topic();

topic.name = req.body.name;
topic.sub_topic.name=req.body.sub_topic

and the data im sending is :(json)

{
    "name":"TestMain",
    "sub_topic":[{"name":"TestSub"}]            
}

UPDATE : got this done using a recursive function.

function subtopicHandler(topic, sub_topic) {
    Topic.find({
      "name": topic.name
    }, function (err, res) {
      if (err) throw err
      return;
    })

    if (sub_topic == undefined) {
      let ntopic = new Topic();
      ntopic.name = topic.name;
      ntopic.sub_topic == undefined;
      ntopic.save(function (err, result) {
        if (err) console.log('saving err', err)
      });
      return ntopic._id;
    }
    let mainTopic = new Topic();
    mainTopic.name = topic.name;
    sub_topic.forEach(function (sub) {
      mainTopic.sub_topic.push(subtopicHandler(sub, sub.sub_topic));
    })
    var retME;
    mainTopic.save(function (err, result) {
      if (err) {
        console.log('saving err', err)
        throw err;
      }
    });
    return mainTopic._id;

  }

Using this schema :

const TopicSchema = new mongoose.Schema({
    name: {type:String,unique:true},
    sub_topic:[{type:mongoose.Schema.Types.ObjectId, ref : 'Topic'}] 
});

and data sent as :

{
    "name":"A",
    "sub_topic":[
                    {"name":"C","sub_topic":
                        [
                            {"name":"C1"}
                            ,
                            {"name":"C2"}
                        ]
                    }
                    ,
                    {"name":"B"}
                    ,
                    {"name":"D","sub_topic":
                        [
                            {"name":"D1"}
                            ,
                            {"name":"D2"}
                            ,
                            {"name":"D3"}
                        ]
                    }
                ]            
}

to the API endpoint handled this way:

let mainTopic = new Topic();
    mainTopic.name = req.body.name;
    subtopicHandler(mainTopic, req.body.sub_topic);
  })

Answer 1

If you are sending following json

const obj = {
    "name":"TestMain",
    "sub_topic":[{"name":"TestSub"}]            
}

Then,

let mainTopic = new Topic();
let subTopic = new Topic();

// assuming for now you have only one sub-topic in array
subTopic.name = obj[0].name;

subTopinc.save(function(err,result)=>{
    if(!err){
        mainTopic.name = obj.name;
        mainTopic.sub_topic = [result._id]
        mainTopic.save(function(err,result){
            console.log(result);
        })
    }
});

From you schema definition and the given json you can follow the above step to get the results.

Hope this will help you.

Answer 2

You can do this with sub docs check out the documentation.

https://mongoosejs.com/docs/subdocs.html