SilverStripe\Forms\MultiSelectField not saving into many_many_extraFields

[elbroto]

Module version(s) affected

6.x, 5.x, 4.x

Description

I wanted to save values from a CheckboxSetField into a many_many_extraFields Text field. Doing this with a standard TextField works fine, but any MultiSelectField fails. The way MultiSelectField->saveInto() is implemented does not work with the ManyMany[Ranking] declaration.
However the ManyMany[]-prefix is required. Without that field being present, in GridFieldDetailForm_ItemRequest->getExtraSavedData() the line $record->hasField($savedField) returns false and no $extraData will be available in GridFieldDetailForm_ItemRequest->saveFormIntoRecord()

I hope this makes sense. I spend a few hours debugging this and my brain is a bit mushy. Please see my sample code. Some breakpoints at the places mentioned above will help as well :)

How to reproduce

1. Clean Installation.
2. Use the first code example.
3. Add a team
4. Add a Supporter to the team, change some checkboxes and save
5. Refresh and/or SELECT * FROM Team_Supporters

class TeamModelAdmin extends \SilverStripe\Admin\ModelAdmin {
    private static $url_segment = 'teams';
    private static $managed_models = [
        Team::class,
        Supporter::class,
    ];
}

class Team extends \SilverStripe\ORM\DataObject {
    private static $many_many = [
        'Supporters' => Supporter::class,
    ];

    private static $many_many_extraFields = [
        'Supporters' => [
            'Ranking' => 'Text',
        ],
    ];

    public function getCMSFields() {
        $this->beforeUpdateCMSFields(function ($fields) {
            if (!$this->isInDB())
                return;

            $gfConfig = \SilverStripe\Forms\GridField\GridFieldConfig_RelationEditor::create();
            $detailform = $gfConfig->getComponentByType(\SilverStripe\Forms\GridField\GridFieldDetailForm::class);
            $values = ['a', 'b', 'c', 'd'];
            $values = array_combine($values, $values);

            $detailform->setFields(\SilverStripe\Forms\FieldList::create(
                \SilverStripe\Forms\CheckboxSetField::create('ManyMany[Ranking]', null, $values),
            ));

            $fields->dataFieldByName('Supporters')->setConfig($gfConfig);
        });

        return parent::getCMSFields();
    }
}

class Supporter extends \SilverStripe\ORM\DataObject {}

In order to make it work without core hacking, I had to do the following changes. I would be fine with most of them, but overriding Supporter->__construct() seems a bit hacky.

class Team extends \SilverStripe\ORM\DataObject {

    // [...]

    public function getCMSFields() {
        $this->beforeUpdateCMSFields(function ($fields) {
            if (!$this->isInDB())
                return;

            $gfConfig = \SilverStripe\Forms\GridField\GridFieldConfig_RelationEditor::create();
            $detailform = $gfConfig->getComponentByType(\SilverStripe\Forms\GridField\GridFieldDetailForm::class);
            $values = ['a', 'b', 'c', 'd'];
            $values = array_combine($values, $values);

            $detailform->setFields(\SilverStripe\Forms\FieldList::create(
                \SilverStripe\Forms\CheckboxSetField::create('ManyMany[Ranking]', null, $values),
            ));
            $detailform->setItemEditFormCallback(function (\SilverStripe\Forms\Form $form) {
                $record = $form->getRecord();
                // without the following chain the updated values would be visible only after a page reload
                $valCurrent = $record->getField('ManyMany[Ranking]') ?? $record->getField('Ranking') ?? '[]';
                $field = $form->Fields()->dataFieldByName('ManyMany[Ranking]');
                $field->setValue(json_decode($valCurrent));
            });

            $fields->dataFieldByName('Supporters')->setConfig($gfConfig);
        });

        return parent::getCMSFields();
    }
}

class Supporter extends \SilverStripe\ORM\DataObject {
    public function __construct($record = [], $creationType = self::CREATE_OBJECT, $queryParams = []) {
        parent::__construct($record, $creationType, $queryParams);

        $this->setField('ManyMany[Ranking]', $this->getField('Ranking'));
    }
}

Possible Solution

A better implementation of MultiSelectField->saveInto() / loadFrom() with checking if $fieldName starts with 'ManyMany[' seems to have the least friction?

Additional Context

No response

Validations

• Check that there isn't already an issue that reports the same bug
• Double check that your reproduction steps work in a fresh installation of silverstripe/installer (with any code examples you've provided)