Add support for embedding and prefetching

[fzaninotto]

Problem

Pages aggregating data from more than one resource always have to fetch more than one API endpoint in cascade, and with a slow backend this leads to an incomplete and blinking UI.

For example, the Comment list page in the simple example shows the post for each comment. So it has to fetch dataProvider.getList('comments'), then dataProvider.getMany('posts', { ids: [comment postIds] }) (via <ReferenceField>).

Some backends are capable of embedding related records (e.g. the post of a comment). However, populating the cache based on these embeds is cumbersome.

Solution

• Allow developers to embed related data in the main data
• Allow developers to prefetch related records and populate the cache with it

TODO

• Allow every data provider method to return a response meta
• Update useDataProvider to populate query cache when a response contains a meta: { prefetched }
• Add support for embedding and prefetching to ra-data-fakerest
• Add support for embedding to ra-data-json-server
• [ ] Add support for embedding and prefetching to ra-data-simplerest(out of scope)
• Update the simple example to use prefetch in the comment list and show views.
• add tests
• Add doc

const CommentList = () => (
    <ListBase queryOptions={{ meta: { prefetch: ['post'] } }}>
        <ListView />
    </ListBase>
);

[djhi]

Note: json-server supports embeds

[slax57]

Incredible feature! And the actual implementation is actually not as hard as I would have imagined.
Love it!