ember js association access backend nodejs mongoose

I am a noob in Ember js/node js/mongo db, and find hard to implement a simple case. I am using nodejs with mongoose as the backend, and emberjs for front end. The requirement is:

A user can belong to many organizations and an organization can have many users. A user can be admin or a customer. This is how I have modelled this in the backend:

models/organization.js

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

var OrganizationSchema = new Schema({
  org_name: String,
  org_address: String,
  org_admins: [{ type: Schema.Types.ObjectId, ref: 'User' }],
  org_customers: [{ type: Schema.Types.ObjectId, ref: 'User' }]
});

module.exports = mongoose.model('Organization',OrganizationSchema);

models/user.js

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

var UserSchema = new Schema({
   username: {type: String, unique: true},
   password: String,
   role: String,
   //organizations: [{type: Schema.Types.ObjectId, ref: 'Organization'}]
});

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

then I have CRUD for Users. I created some organizations storing some users ids as org_admins, and some as org_customers.

I want to create an index view, where all the organizations come up, with corresponding admins and corresponding customers.

This is how the basic template appears on the browser now:

Organizations:
Org1  address1
admins:

5534a5172751c5b05b7e7cd0
5534cb359262868030211796
Customers:


org2  address2
admins:

5534a5172751c5b05b7e7cd0
customers:
5534cb359262868030211796

I want the username of the admins and username of the customers to be displayed.

This is the Ember side code:

app/models/organization.js

import DS from 'ember-data';

export default DS.Model.extend({
  org_name: DS.attr('string'),
  org_address: DS.attr('string'),
  org_admins: DS.attr(),
  org_customer: DS.attr()

});

app/models/user.js

import DS from 'ember-data';

var User =  DS.Model.extend({
username: DS.attr('string'),
password: DS.attr('string'),
role: DS.attr('string')
});

export default User;

This is the template file app/templates/organization.hbs

<ul>
Organizations: 
<p>
{{#each organization in model}}
<li>
<label> {{organization.org_name}} </label>
<label> {{organization.org_address}}</label>
<p> <label> admins: </label></p>
 <ul>
  {{#each admin in organization.org_admins}} 
   <li>{{admin}}</li>
  {{/each}}
</ul>


<p> <label> Customers: </label></p>
 <ul>
  {{#each customer in organization.org_customers}} 
   <li>{{customer}}</li>
  {{/each}}
</ul>
</li>
{{/each}}
</p>
</ul>


<p>
<button {{action 'neworganization'}} > Add Organization </button>
</p>

{{outlet}}

The routes file app/routes/organizations.js

import Ember from 'ember';

export default Ember.Route.extend({
    model: function(){
    return this.store.find('organization');
}
});

I proceeded by getting the username in the controller, but it didnt work. I understand I am doing something wrong in modelling the associations. I also tried using DS.hasMany instead of DS.attr(), but could not achieve my motive, I may be doing something wrong, not understanding the associations properly.

What is the right way I could do this. Please help.