What is the Handling Metadata in Ember.js?

Ember.js - Interview Questions

Along with the records returned from your store, you'll likely need to handle some kind of metadata. Metadata is data that goes along with a specific model or type instead of a record.

Pagination is a common example of using metadata. Imagine a blog with far more posts than you can display at once. You might query it like so:

let result = this.store.query('post', {
  limit: 10,
  offset: 0
});

Each serializer will expect the metadata to be returned differently. For example, Ember Data's JSON deserializer looks for a meta key:

{
  "post": {
    "id": 1,
    "title": "Progressive Enhancement is Dead",
    "comments": ["1", "2"],
    "links": {
      "user": "/people/tomdale"
    },
    // ...
  },

  "meta": {
    "total": 100
  }
}

Regardless of the serializer used, this metadata is extracted from the response. You can then read it with .meta.

This can be done on the result of a store.query() call :

store.query('post').then(result => {
  let meta = result.meta;
});

On a belongsTo relationship :

let post = store.peekRecord('post', 1);

let author = await post.author;
let meta = author.meta;

Or on a hasMany relationship :

let post = store.peekRecord('post', 1);

let comments = await post.comments;
let meta = comments.meta;

After reading it, meta.total can be used to calculate how many pages of posts you'll have.

To use the meta data outside of the model hook, you need to return it:

app/routes/users.js :

import Route from '@ember/routing/route';
import { service } from '@ember/service';

export default class UsersRoute extends Route {
  @service store;

  model() {
    return this.store.query('user', {}).then((results) => {
      return {
        users: results,
        meta: results.meta
      };
    });
  }
  setupController(controller, { users, meta }) {
    super.setupController(controller, users);
    controller.meta = meta;
  }
}

To customize metadata extraction, check out the documentation for your serializer.