TYPO3 TCA relations not by uid field

Question

In my TCA I have relation n:1 SuperClass -> Code

    'super_class' => [
        'exclude' => true,
        'label' => 'Super Class',
        'config' => [
            'type' => 'select',
            'renderType' => 'selectSingle',
            'foreign_table' => 'tx_classification_item',
            'minitems' => 0,
            'maxitems' => 1,
        ],
    ],

Field "super_class" related to field "uid". I need to set relation between "super_class" and "code" fields, not "uid" field. Can I do it?

Answer 1

Right in the docs, section "Simple 1:n relation". https://docs.typo3.org/typo3cms/TCAReference/ColumnsConfig/Type/Inline.html

You're looking for the config option 'foreign_table_field', which defines the relation field in the foreign table. This should do the trick for you:

'super_class' => [
    'exclude' => true,
    'label' => 'Super Class',
    'config' => [
        'type' => 'select',
        'renderType' => 'selectSingle',
        'foreign_table' => 'tx_classification_item',
        'foreign_table_field' => 'code',
        'minitems' => 0,
        'maxitems' => 1,
    ],
],

Answer 2

I'm really sure, that this isn't possible for selects, but it's possible for inline elements. There you can use the field foreign_table_field. Otherwise you could use a user function for that:

'config' => [
    'type' => 'user',
    'userFunc' => YYY\XXX\TCA\TcaReferenceField::class . '->render',
]

The code would be something like this:

public function render(array $configuration, UserElement $userElement) {
    $row = $configuration['row'];

    // Do some Magic here.

    $select = '<label style="font-weight: 400;">' . self::MESSAGE_FIELD_LABEL;
    $select .= '<select name="' . $configuration['itemFormElName'] . '" class="form-control form-control-adapt" ' .
    'onchange=\'' . $configuration['fieldChangeFunc']['alert'] . '\'>';
    $select .= '<option value=""></option>';
    foreach ($contentElementUids as $siteName => $contentElementUid) {
        $isSelected = ($contentElementUid === (int) $configuration['itemFormElValue']);
        $select .= '<option ' . ($isSelected ? 'selected' : '') . ' value="' . $contentElementUid . '">' .
        $siteName . '</option>';
    }
    $select .= '</select></label>';

    return $select;
}