Nodal TL;DR Many-to-Many Relationship

1. Command Line

npm install -g nodal
nodal new many-to-many
cd many-to-many
nodal g:model User name:string
nodal g:model Group name:string
nodal g:controller v1 --for Users
nodal g:controller v1 --for Groups
nodal g:model UserGroup user_id:int group_id:int
nodal g:controller v1 --for UserGroup
nodal db:create
nodal db:prepare
nodal db:migrate
nodal db:seed

2. seed.json

/* config/seed.json */
{

  "development": {
    "User": [
      {"name": "Kevin"}, 
      {"name": "Michelle"}, 
      {"name": "Connie"}, 
      {"name": "Liam"}
    ],
    "Group": [
      {"name": "deluxe-pug" },
      {"name": "savory-penguin"},
      {"name": "sabine-sardine"}
    ]
  },

  "test": {},

  "production": {}

}

3. user_groups_controller.js

module.exports = (function() {

  'use strict';

  const Nodal = require('nodal');
  const UserGroup = Nodal.require('app/models/user_group.js');
  const //import models

  class V1UserGroupsController extends Nodal.Controller {

    index() {

      UserGroup.query()
        .where(this.params.query)
        .end((err, models) => {

          this.respond(err || models);

        });

    }

    show() {

      UserGroup.find(this.params.route.id, (err, model) => {

        this.respond(err || model);

      });

    }


    create() {

      let user_id;
      let group_id;
      let user_group;
      const userName = { name: this.params.body.userName };
      const groupName = { name: this.params.body.groupName };

      User.findOrCreateBy("name", userName, (err, user) => {
        if ( err ) { return this.respond(err); } // make sure your handle error
        user_id = user.get('id');

        Group.findOrCreateBy("name", groupName, (err, group) => {
          if ( err ) { return this.respond(err); } // every step!!!
          group_id = group.get('id');

          user_group = { user_id, group_id };
          
          UserGroup.create(user_group, (err, userGroup) => {
            this.respond(err || userGroup);
          });

        });

      });

    }

    update() {

      UserGroup.update(this.params.route.id, this.params.body, (err, model) => {

        this.respond(err || model);

      });

    }

    destroy() {

      UserGroup.destroy(this.params.route.id, (err, model) => {

        this.respond(err || model);

      });

    }

  }

  return V1UserGroupsController;

})();