TYPO3 / TYPO3.CMS

        // Fetch tableRelationFields and save them in cache if not there yet

        $cacheId = static::$cachePrefixTableRelationFields . $tableName;

        if (!$this->useRuntimeCache || !$this->runtimeCache->has($cacheId)) {

            $tableRelationFields = $this->fetchTableRelationFields($tableName);

            $this->runtimeCache->set($cacheId, $tableRelationFields);

        } else {

            $tableRelationFields = $this->runtimeCache->get($cacheId);

        }

        $connectionPool = GeneralUtility::makeInstance(ConnectionPool::class);

        $connection = $connectionPool->getConnectionForTable('sys_refindex');

            // Fetch fields of the table which might contain relations

            $cacheId = static::$cachePrefixTableRelationFields . $tableName;

            if (!$this->useRuntimeCache || !$this->runtimeCache->has($cacheId)) {

                $tableRelationFields = $this->fetchTableRelationFields($tableName);

                if ($this->useRuntimeCache) {

                    $this->runtimeCache->set($cacheId, $tableRelationFields);

                }

            } else {

                $tableRelationFields = $this->runtimeCache->get($cacheId);

            }

            // Return if there are no fields which could contain relations

            if ($tableRelationFields === '') {