Data access POC (discussion)

[alexandru-calinoiu]

What does it fix?

This is a POC (prove of concept) for data access, it will add api integration for the discovery screen.

To kick start discussions I will try to walk you through my thought process.

• Our journey starts, like all refactoring stories start, with adding tests for the feature we want to refactor, first commit will add tests for DiscoveryViewModel in order to make sure we don't break anything with the next commits.
• We then add the ThemesRepository with this commit. We add the repository in our feature module as close as possible to our screen. This will allow us full control of what we bring from our datasource and future developers working on this feature have the data fetching right there and don't have to worry about compatibility with other screen/features. Notice that tests did not actually change as functionality there was a slight rename that was needed.
• We continue naturally by adding a graphql query to our feature with this commit is order to achieve this we use the multi modules feature of apollo3. Again because the queries are at the feature level (in the learn module) we can craft them to serve the needs of the functionalities in this module, this is great because graphql allows us exactly this to query only the fields we need.
• We wrap thing up with a small refactoring the ui model, common/ui/models/LessonTheme should have no idea about the underlying datasource, it should only exist so that the composable/LessonThemesItem can be evolved without actually carrying about the api.

One might think that with this approach there might be some duplication, this indeed can happen, I need themes both in the home and learn feature, so this means I will write the same query twice? You can very well write the same query twice, but this approach allows you to write only one query in the home screen that will bring both lessons and themes saving a trip to the api.

TL;TR: developers should be able to work in parallel and isolation to ui composables and any feature module

How has it been tested?

• start the app
• navigate to the discovery screen

TODO:

• use the string id's
• use the image from the api

[daniyelp]

It looks like the way to go. It takes advantage of what GraphQL offers over REST, we don't over fetch data and we minimize the number of API calls. It decouples more the feature modules. Now that we have to repeat ourselves a little is not that much of an inconvenient if we take into consideration the benefits of the approach.