[5.8] Add deleted_at date cast for soft deleting models

[timacdonald]

This PR utilises a trait initializer to automatically add deleted_at to the $dates array of any model that uses the SoftDeletes trait. Previously this has to be added manually to each model - unlike the created_at and updated_at that is handled "under the hood".

In essence...

class Post extends Eloquent
{
    use SoftDeletes;

    // no need for this anymore
    // protected $dates = ['deleted_at'];
}

Notes:

• An existing$casts entry for deleted_at will take precedence (test exists).
• A duplicate $dates entry for deleted_at will have no impact as the array is not a key => value pair, but a value array. Also when getDates is called it already runs array_unique to remove any duplicate entries (test exists).
• An existing mutator getDeletedAtAttribute will take precedence (test exists).

Breaking:

This will be a breaking change if you are not expecting the value of deleted_at to be cast, i.e. you never added it to the $dates array as outlined in the docs. But as mentioned earlier, a mutator will take precedence if for whatever reason you don't want the automatic casting.

[taylorotwell]

Is there any path for opting out of the cast?

[timacdonald]

Just added a new test to confirm the current behaviour can be maintained by adding a cast.

This is the easiest opt-out and the one I see being in the upgrade guide if this PR was to be accepted. A boolean toggle seemed like overkill as the cast is a one-liner.

protected $casts = [
    'deleted_at' => 'string', // retain current functionality
]; 

It is also possible to opt-out with an attribute mutator - but obviously that is more than a one liner.

The order of precedence is:

1. Mutator
2. $casts
3. $dates

If you feel a boolean toggle opt-out attribute would be the best way I will happily add that.

Edit: I think there might be some other cases I need to consider that the cast to string might not handle and perhaps a Boolean toggle to opt out would be best. Will take a look at them tomorrow.

[timacdonald]

After sitting on this for the day I think the boolean flag is the better overall approach. I've implemented it in a seperate commit, so you can roll it back if you prefer opting out via a cast to string as mentioned above.

With the current PR you can opt-out by setting the boolean flag on the model (test exists)...

class Post extends Eloquent
{
    // opt-out of the automatic casting...
    protected $castDeletedAtToDateInstance = false;
}

[driesvints]

Not that I have a better alternative but the current property name looks super confusing and long..

[taylorotwell]

Eh, I think I prefer the string cast to the property.

[timacdonald]

Just reverted and removed the boolean flag. However Travis is said to have failed - but as I'm looking at it right now it actually hasn't run the tests. Not sure if you can whack it with a big spanner to get it to run again?

[taylorotwell]

Merged.