[8.x] Load collection relations on serialisation restore

[joshhanley]

This PR ensures collection relations are restored after an eloquent collection has been serialised.

This feature was introduced in PR #21191 for single models, and merged in PR #21229, with this feature to be added to collections in a later PR (as noted on the original PR). But I couldn't find any follow up PR that added this.

The use-case I have for this, is for Livewire.

Livewire uses this feature to serialise and restore model properties and eloquent collection properties. Currently model properties restore correctly, but eloquent collections do not, causing an n+1 problem when blade templates iterate through any relations. See this issue on Livewire repo as an example livewire/livewire#2010.

Hope this helps!

[taylorotwell]

I am personally wary of changing this behavior on a patch release. We are having way too many accidental breaking changes lately.

[joshhanley]

@taylorotwell yeah fair enough. Can I add any more tests that would make you comfortable merging this into 8.x or would you prefer I sent this to master?

[austenc]

Although it could be solved on the Livewire side, this seems like it'd be an improvement to the serialization features of the framework instead. Think I've run into this in the past when using queued jobs too. If you're dealing with a ton of relations it seems like it could slow things down, but that's the only potentially bad scenario that comes to mind.

Any other potential downsides you can think of?

[calebporzio]

Just chiming in to echo what Josh and Austen have said.

I consider this expected behavior because Laravel already preserves single model relationships.

You would expect model collections to do the same.

We can solve this on the Livewire side, but would be a great upstream Laravel fix to have in core so people could benefit when dealing with Queues.

[driesvints]

I think a new PR to master can be reconsidered maybe. Seems like Taylor just doesn't wants to do this on the current stable release.

[bilfeldt]

@driesvints is this worth reconsidering as something worth including in th upcoming Laravel 9? 🤞 Of cause that deadline is approaching fast 😄