Nested fields and expand in REST API

[yii-bot]

This issue has originally been reported by @ghost at yiisoft/yii2#8061.
Moved here by @samdark.

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Facebook Graph API also uses fields and expand query parameters in REST APIs. Now Yii2 supports same but upto 1 level. Can we do nested fields like Facebook, for example:

GET graph.facebook.com/me?fields=albums.limit(5){name, photos.limit(2){name, picture, tags.limit(2)}},posts.limit(5)

In above example, my albums are limits to 5 only and again in each album only name and photos fields will be fetched with max 2 photos per album with again photos nested to give max 2 tags per photo. Along with albums, it will also give max 5 posts of the user.

Now limit(n) would be advance feature but I think nested expand is something easy to implement and really necessary feature to have.

PS: On separate note if you plan to support nested limit, you can also look into offset and sort on nested elements.

[samdark]

Great to have this as a feature.