Ember Substates with Ember data after store already has data

Question

I have read Ember docs related to Substates etc and I understand how it works. In my current application my loading.hbs and other child loading.hbs templates work fine.

I just want to discuss a use case.

1. In my route A, in my model function I do fetchAll for my model.
2. I go to Route A, First time api request is sent and I see my loading screen.
3. now I navigate to some other route B.
4. now I come back to first route A, api request is sent again but this time loading screen is not shown.

I want to develop my understanding here. Now the second time loading screen is not shown which tells us that store had data so there is no sense to put it on loading and after fetch store sent request to sync with backend.

QUESTION

Now I want to know if this is a default behaviour of Ember with Ember-data?

To show this loading screen, will I have to do something manually?

Ideally what I want is, if on second request data was fetched then show it and at the same time show loader to tell user that it is syncing with backend as well.

I know everything can be done manually, I don't want to reinvent the wheel or do things in non-conventional way. So I want to know best optimized solution for this as provided by Ember which an experienced Ember developer can help me understand.

Thanks in advance.

Answer 1

Now I want to know if this is a default behaviour of Ember with Ember-data?

Yes, that's the default behavior of Ember data when you do a findRecord or findAll where shouldBackgroundReloadRecord or shouldBackgroundReloadAll event of the adapter respectively, is defaulted to true. You can turn this off by returning false and ensuring shouldReloadAll or shouldReloadRecord respectively are set at true to ensure the request always hits the API and not fetches from cache.

Ideally, showing data immediately on the screen is always advisable as it has a better UX in terms of giving the user a feel that data is already there and that some parts of the data is being fetched. Check here

To show this loading screen, will I have to do something manually?

You may also want to read this

Answer 2

To add further details after my own research, I found helpful and relevant details in Ember docs.This is all about caching.

If records were already there then promise will be resolved immediately that's why I don't see loading screen for already loaded record, at the same time Ember-Data syncs with backend as well and re-render the template.

Ember Model Docs

Caching The store will automatically cache records for you. If a record had already been loaded, asking for it a second time will always return the same object instance. This minimizes the number of round-trips to the server, and allows your application to render its UI to the user as fast as possible.

For example, the first time your application asks the store for a person record with an ID of 1, it will fetch that information from your server.

However, the next time your app asks for a person with ID 1, the store will notice that it had already retrieved and cached that information from the server. Instead of sending another request for the same information, it will give your application the same record it had provided it the first time. This feature—always returning the same record object, no matter how many times you look it up—is sometimes called an identity map.

Using an identity map is important because it ensures that changes you make in one part of your UI are propagated to other parts of the UI. It also means that you don't have to manually keep records in sync—you can ask for a record by ID and not have to worry about whether other parts of your application have already asked for and loaded it.

One downside to returning a cached record is you may find the state of the data has changed since it was first loaded into the store's identity map. In order to prevent this stale data from being a problem for long, Ember Data will automatically make a request in the background each time a cached record is returned from the store. When the new data comes in, the record is updated, and if there have been changes to the record since the initial render, the template is re-rendered with the new information.