discourse/documentation/chat/frontend/lib_collection.js.html
Martin Brennan 60ad836313
DEV: Chat service object initial implementation (#19814)
This is a combined work of Martin Brennan, Loïc Guitaut, and Joffrey Jaffeux.

---

This commit implements a base service object when working in chat. The documentation is available at https://discourse.github.io/discourse/chat/backend/Chat/Service.html

Generating documentation has been made as part of this commit with a bigger goal in mind of generally making it easier to dive into the chat project.

Working with services generally involves 3 parts:

- The service object itself, which is a series of steps where few of them are specialized (model, transaction, policy)

```ruby
class UpdateAge
  include Chat::Service::Base

  model :user, :fetch_user
  policy :can_see_user
  contract
  step :update_age

  class Contract
    attribute :age, :integer
  end

  def fetch_user(user_id:, **)
    User.find_by(id: user_id)
  end

  def can_see_user(guardian:, **)
    guardian.can_see_user(user)
  end

  def update_age(age:, **)
    user.update!(age: age)
  end
end
```

- The `with_service` controller helper, handling success and failure of the service within a service and making easy to return proper response to it from the controller

```ruby
def update
  with_service(UpdateAge) do
    on_success { render_serialized(result.user, BasicUserSerializer, root: "user") }
  end
end
```

- Rspec matchers and steps inspector, improving the dev experience while creating specs for a service

```ruby
RSpec.describe(UpdateAge) do
  subject(:result) do
    described_class.call(guardian: guardian, user_id: user.id, age: age)
  end

  fab!(:user) { Fabricate(:user) }
  fab!(:current_user) { Fabricate(:admin) }

  let(:guardian) { Guardian.new(current_user) }
  let(:age) { 1 }

   it { expect(user.reload.age).to eq(age) }
end
```

Note in case of unexpected failure in your spec, the output will give all the relevant information:

```
  1) UpdateAge when no channel_id is given is expected to fail to find a model named 'user'
     Failure/Error: it { is_expected.to fail_to_find_a_model(:user) }

       Expected model 'foo' (key: 'result.model.user') was not found in the result object.

       [1/4] [model] 'user' 
       [2/4] [policy] 'can_see_user'
       [3/4] [contract] 'default'
       [4/4] [step] 'update_age'

       /Users/joffreyjaffeux/Code/pr-discourse/plugins/chat/app/services/update_age.rb:32:in `fetch_user': missing keyword: :user_id (ArgumentError)
       	from /Users/joffreyjaffeux/Code/pr-discourse/plugins/chat/app/services/base.rb:202:in `instance_exec'
       	from /Users/joffreyjaffeux/Code/pr-discourse/plugins/chat/app/services/base.rb:202:in `call'
       	from /Users/joffreyjaffeux/Code/pr-discourse/plugins/chat/app/services/base.rb:219:in `call'
       	from /Users/joffreyjaffeux/Code/pr-discourse/plugins/chat/app/services/base.rb:417:in `block in run!'
       	from /Users/joffreyjaffeux/Code/pr-discourse/plugins/chat/app/services/base.rb:417:in `each'
       	from /Users/joffreyjaffeux/Code/pr-discourse/plugins/chat/app/services/base.rb:417:in `run!'
       	from /Users/joffreyjaffeux/Code/pr-discourse/plugins/chat/app/services/base.rb:411:in `run'
       	from <internal:kernel>:90:in `tap'
       	from /Users/joffreyjaffeux/Code/pr-discourse/plugins/chat/app/services/base.rb:302:in `call'
       	from /Users/joffreyjaffeux/Code/pr-discourse/plugins/chat/spec/services/update_age_spec.rb:15:in `block (3 levels) in <main>'
```
2023-02-13 13:09:57 +01:00

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<pre id="source" class="source-page line-numbers"><code class="language-js">import { ajax } from "discourse/lib/ajax";
import { tracked } from "@glimmer/tracking";
import { bind } from "discourse-common/utils/decorators";
import { Promise } from "rsvp";
/**
* Handles a paginated API response.
*/
export default class Collection {
@tracked items = [];
@tracked meta = {};
@tracked loading = false;
constructor(resourceURL, handler) {
this._resourceURL = resourceURL;
this._handler = handler;
this._fetchedAll = false;
}
get loadMoreURL() {
return this.meta.load_more_url;
}
get totalRows() {
return this.meta.total_rows;
}
get length() {
return this.items.length;
}
// https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Iteration_protocols
[Symbol.iterator]() {
let index = 0;
return {
next: () => {
if (index &lt; this.items.length) {
return { value: this.items[index++], done: false };
} else {
return { done: true };
}
},
};
}
/**
* Loads first batch of results
* @returns {Promise}
*/
@bind
load(params = {}) {
this._fetchedAll = false;
if (this.loading) {
return Promise.resolve();
}
this.loading = true;
const filteredQueryParams = Object.entries(params).filter(
([, v]) => v !== undefined
);
const queryString = new URLSearchParams(filteredQueryParams).toString();
const endpoint = this._resourceURL + (queryString ? `?${queryString}` : "");
return this.#fetch(endpoint)
.then((result) => {
this.items = this._handler(result);
this.meta = result.meta;
})
.finally(() => {
this.loading = false;
});
}
/**
* Attempts to load more results
* @returns {Promise}
*/
@bind
loadMore() {
let promise = Promise.resolve();
if (this.loading) {
return promise;
}
if (
this._fetchedAll ||
(this.totalRows &amp;&amp; this.items.length >= this.totalRows)
) {
return promise;
}
this.loading = true;
if (this.loadMoreURL) {
promise = this.#fetch(this.loadMoreURL).then((result) => {
const newItems = this._handler(result);
if (newItems.length) {
this.items = this.items.concat(newItems);
} else {
this._fetchedAll = true;
}
this.meta = result.meta;
});
}
return promise.finally(() => {
this.loading = false;
});
}
#fetch(url) {
return ajax(url, { type: "GET" });
}
}
</code></pre>
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