TYPO3 Core

Can we skip those special values?

In validateTcaType() possibly add check for ':' indicating this is no fieldName directly but points to a "sub-field".

foreach ($tableDefinition['columns'] as $fieldName => $fieldConfig) {
                if ((strpos($fieldName, ':') === false) && isset($fieldConfig['config']) && is_array($fieldConfig['config']) && empty($fieldConfig['config']['type'])) {

A Workaround that worked for me is to XClass the \TYPO3\CMS\Extbase\Persistence\Generic\Mapper\DataMapper and override the method: getTargetType. What needs to be done is to check if the array key is present in the $row before using it:

/**
     * Returns the target type for the given row.
     *
     * @param string $className The name of the class
     * @param array $row A single array with field_name => value pairs
     * @return string The target type (a class name)
     */
    public function getTargetType($className, array $row)
    {
        $dataMap = $this->getDataMap($className);

        $targetType = $className;
        if ($dataMap->getRecordTypeColumnName() !== null) {
            foreach ($dataMap->getSubclasses() as $subclassName) {
                $recordSubtype = $this->getDataMap($subclassName)->getRecordType();

                // Check if column is present in the row
                if (array_key_exists($dataMap->getRecordTypeColumnName(), $row) && (string)$row[$dataMap->getRecordTypeColumnName()] === (string)$recordSubtype) {
                    $targetType = $subclassName;
                    break;
                }
            }
        }
        return $targetType;
    }

The method is based on TYPO3 V11.5.27

Seems like Extbase never did support the <relation-field>:<related-table-field> notation.

In the backend the BackendUtility::getTCAtypeValue() method can be used to resolve this. Thus a possible fix in DataMapper::getTargetType() could be using this:

+use TYPO3\CMS\Backend\Utility\BackendUtility;

-                if ((string)$row[$dataMap->getRecordTypeColumnName()] === (string)$recordSubtype) {
+                if (BackendUtility::getTCAtypeValue($this->convertClassNameToTableName($className), $row) === (string)$recordSubtype) {