Fix related records auto-save with belongsTo() relation

[gponcon]

Hello!

• Type: bug fix
• Link to issue: [BUG]: When updating including a relation, the relation destination is not updated #15148

In raising this pull request, I confirm the following:

• I have read and understood the Contributing Guidelines
• I have checked that another pull request for this purpose does not exist
• I wrote some tests for this PR
• I have updated the relevant CHANGELOG
• I have created a PR for the documentation about this change

Small description of change:

Models: with a relation belongsTo() - hasMany(), the related records need to be saved in preSaveRelatedRecords(). This fix update the dirtyState of related records to trigger related records save.

[gponcon]

Note that this fix may not be perfect because when you access a linked record it seems to be saved anyway.

According to my tests:

$invoice = Invoices::findFirst();
$invoice->customer->name = "name";
$invoice->save(); // customer is saved 👍 

$invoice = Invoices::findFirst();
$invoice->save(); // customer is not saved 👍 

$invoice = Invoices::findFirst();
echo $invoice->customer->name;
$invoice->save(); // customer is saved 👎 

Maybe there is something to do in __set() or somewhere else?

[zsilbi]

$invoice = Invoices::findFirst();
echo $invoice->customer->name;
$invoice->save(); // customer is saved 👎 

Maybe there is something to do in __set() or somewhere else?

We don't have knowledge about the state of the properties in (related) models.
If the a relatation has been accessed in any way, we will have to save that record, because it could have been modified since the query.
To eliminate this, we would have to enforce using snapshots (which is not a possibility) and compare them to their current state before each action.

dirtyState does not reflect on property changes, it only indicates if the record is saved to the database.

[gponcon]

$invoice = Invoices::findFirst();
$invoice->save(); // customer is not saved 👍

What do you expect to be saved for customer in this case?

customer is not saved because it hasn't been accessed, which sounds pretty good.

[gponcon]

(...)
We don't have knowledge about the state of the properties in (related) models.
If the a relatation has been accessed in any way, we will have to save that record, because it could have been modified since the query.
To eliminate this, we would have to enforce using snapshots (which is not a possibility) and compare them to their current state before each action.

dirtyState does not reflect on property changes, it only indicates if the record is saved to the database.

Thank you for this clarification. Indeed, I did not know how to deal with dirtyState for this resolution.

[niden]

@gponcon Thank you so much for the bug fix. Could you please change your target branch to be 5.0.x? We never send PRs to master unless it is a release

It is looking good

[gponcon]

@niden I modified the target branch as requested. Let me know if it is correct, I am at your disposal.

[niden]

@gponcon Can you please rebase to the latest 5.0.x branch and add an entry to the changelog? Then we can merge this

[niden]

Closing in favor of #15838. Original work preserved