在Extbase扩展中$this->cObj在当前范围内已经没有可用了，所以需要先获取你可以使用:

In Extbase extensions $this->cObj is no more available in the current scope, so you need to get it first before you can use:

$cObj = $this->configurationManager->getContentObject();

$ttContentConfig = array(
    'tables'       => 'tt_content',
    'source'       => 123,
    'dontCheckPid' => 1
);

$content .= $cObj->RECORDS($ttContentConfig);