[TYPO3-english] TCA relations not by uid field

[Dmitry]

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? 
-- 
Kind regards,
Dmitry Vasilev
www: http://typo3.ru.net/
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Phone: +7 950 001 85 15