[Bug] Original data persists when emptying a relationship field with inline_create

[WayneFrisby]

Bug report

What I did

I have created many relationship fields. Most work fine.
Tags with Polymorphic relationships work with no casting on its Model.

Yet, on my Business Model I have this relationship and casting to an array

// Business Model
protected $casts = [
    'phones' => 'array', // Required to get it working
];

public function phones()
{
    return $this->hasMany(Phone::class);
}

// Phone Model
public function business()
{
    return $this->belongsTo(Business::class);
}

without 'inline_create' set to true with the entity set, it works fine, but once set with like this

'inline_create' => [ 'entity' => 'phone' ],

I can't make it null once I have any current-value's set.

Everything else works as expected, but once I've added anything to the database, it's impossible (in the UI) to go back to an empty state.

What I expected to happen

Once deleting all items (in this case, phone numbers) then saving, it updates to an empty state.

What happened

The same or similar to #2760

It remains populated with the original value(s).
I can remove many items to 1 fine, but many/one to none, the original data persists.

What I've already tried to fix it

Many things.

I've tried comparing to working relationship fields. Only difference being the relationships and casting to array (due to JSON string) versus no casting (returns Collection).

Dug into the fetch_or_create file as this seems like where the issue may be.

When clearing the select box the <select> <option>'s remain, yet disappear from the render block. At first I thought this was a bug (might still be?), yet this seems to happen all the time, even on working fields. So I'm guessing that's just how select2 works? Seems odd, but maybe some sort of accessibility thing? We add options (to the select), but never remove them.

The only way I've manged to get it to work (not persist) is to set one <option> to an empty value via the dev tools, then save.

As for the field definition, I've tried many variations with no luck.

            [   
                'name'    => 'phones',
                'type'    => 'relationship',
                'ajax'          => true,
                'inline_create' => [ 'entity' => 'phone' ],
                'attribute' => "number",
                'minimum_input_length' => 0,
                'allows_null' => true,
            ],
           
            // Simplified
            [   
                'name'    => 'phones',
                'type'    => 'relationship',
                'ajax'          => true, // Not sure this makes any difference
                'inline_create' => [ 'entity' => 'phone' ], // Required for desired feature, works fine without but I want it
                'allows_null' => true, // Not sure this makes any difference
            ],

Backpack, Laravel, PHP, DB version

When I run php artisan backpack:version the output is:

PHP VERSION:

PHP 7.4.3 (cli) (built: Oct 6 2020 15:47:56) ( NTS )
Copyright (c) The PHP Group
Zend Engine v3.4.0, Copyright (c) Zend Technologies
with Zend OPcache v7.4.3, Copyright (c), by Zend Technologies

LARAVEL VERSION:

v8.28.1@73dd43d92fcde6c6abc00658ae33391397ca119d

BACKPACK VERSION:

4.1.x-dev@62856b1f01fc3e05c80140fc22f85ea2aac8368c

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[pxpm]

Hello @WayneFrisby thanks for the report.

Indeed InlineCreate was not designed for HasMany relation, because in HasMany the related key is stored on the related model, and not in the current one like BelongsTo. It could work but only on update because you need to have the current entry key to setup in the related model.

We are in the process of providing that functionality but it's through a different field, repeatable.

PR is here: #3410

If you want to give it a try, let us know the results.

Best,
Pedro

[pxpm]

I am going to close this due to inactivity. The solution is beeing provided in the mentioned PR.