Specifying a Route's Model

Some routes always display the same model. For example, the /photos route will always display the same list of photos available in the application. If your user leaves this route and comes back later, the model does not change.

However, you will often have a route whose model will change depending on user interaction. For example, imagine a photo viewer app. The /photos route will render the photos template with the list of photos as the model, which never changes. But when the user clicks on a particular photo, we want to display that model with the photo template. If the user goes back and clicks on a different photo, we want to display the photo template again, this time with a different model.

In cases like this, it's important that we include some information in the URL about not only which template to display, but also which model.

In Ember, this is accomplished by defining routes with dynamic segments.

Once you have defined a route with a dynamic segment, Ember will extract the value of the dynamic segment from the URL for you and pass them as a hash to the model hook as the first argument:

Router.map(function() {
  this.route('photo', { path: '/photos/:photo_id' });
});

import Route from '@ember/routing/route';

export default Route.extend({
  model(params) {
    return this.get('store').findRecord('photo', params.photo_id);
  }
});

In the model hook for routes with dynamic segments, it's your job to turn the ID (something like 47 or post-slug) into a model that can be rendered by the route's template. In the above example, we use the photo's ID (params.photo_id) as an argument to Ember Data's findRecord method.

Note: A route with a dynamic segment will always have its model hook called when it is entered via the URL. If the route is entered through a transition (e.g. when using the link-to Handlebars helper/), and a model context is provided (second argument to link-to), then the hook is not executed. If an identifier (such as an id or slug/) is provided instead then the model hook will be executed.

For example, transitioning to the photo route this way won't cause the model hook to be executed (because link-to was passed a model/):

<h1>Photos</h1>
{{#each model as |photo|}}
  <p>
    {{#link-to "photo" photo}}
      <img src="{{photo.thumbnailUrl}}" alt="{{photo.title}}" />
    {{/link-to}}
  </p>
{{/each}}

while transitioning this way will cause the model hook to be executed (because link-to was passed photo.id, an identifier, instead):

<h1>Photos</h1>
{{#each model as |photo|}}
  <p>
    {{#link-to "photo" photo.id}}
      <img src="{{photo.thumbnailUrl}}" alt="{{photo.title}}" />
    {{/link-to}}
  </p>
{{/each}}

Routes without dynamic segments will always execute the model hook.

Multiple models can be returned through an RSVP.hash. The RSVP.hash method takes an object with promises or values as properties as an argument, and returns a single promise. When all of the promises in the object resolve, the returned promise will resolve with an object of all of the promise values. For example:

import Route from '@ember/routing/route';
import RSVP from 'rsvp';

export default Route.extend({
  model() {
    return RSVP.hash({
      songs: this.get('store').findAll('song'),
      albums: this.get('store').findAll('album')
    });
  }
});

In the songs template, we can specify both models and use the {{#each}} helper to display each record in the song model and album model:

<h1>Playlist</h1>

<ul>
  {{#each model.songs as |song|}}
    <li>{{song.name}} by {{song.artist}}</li>
  {{/each}}
</ul>

<h1>Albums</h1>

<ul>
  {{#each model.albums as |album|}}
    <li>{{album.title}} by {{album.artist}}</li>
  {{/each}}
</ul>

If you use Ember Data and you are building an RSVP.hash with the model's relationship, consider instead properly setting up your relationships and letting Ember Data take care of loading them.

Sometimes you need to fetch a model, but your route doesn't have the parameters, because it's a child route and the route directly above or a few levels above has the parameters that your route needs.

In this scenario, you can use the paramsFor method to get the parameters of a parent route.

import Route from '@ember/routing/route';

export default Route.extend({
  model() {
    let { album_id } = this.paramsFor('album');

    return this.store.query('song', { album: album_id });
  }
});

This is guaranteed to work because the parent route is loaded. But if you tried to do paramsFor on a sibling route, you wouldn't have the results you expected.

This is a great way to use the parent context to load something that you want. Using paramsFor will also give you the query params defined on that route's controller. This method could also be used to look up the current route's parameters from an action or another method on the route, and in that case we have a shortcut: this.paramsFor(this.routeName).

In our case, the parent route had already loaded its songs, so we would be writing unnecessary fetching logic. Let's rewrite the same route, but use modelFor, which works the same way, but returns the model from the parent route.

import Route from '@ember/routing/route';

export default Route.extend({
  model() {
    let { songs } = this.modelFor('album');

    return songs;
  }
});

In the case above, the parent route looked something like this:

import Route from '@ember/routing/route';
import RSVP from 'rsvp';

export default Route.extend({
  model({ album_id }) {
    return RSVP.hash({
      album: this.store.findRecord('album', album_id),
      songs: this.store.query('songs', { album: album_id })
    });
  }
});

And calling modelFor returned the result of the model hook.