code: public function getHTMLFragments($gridField) {
  		$dataClass = $gridField->getList()->dataClass();
  		$obj = singleton($dataClass);
  		if(!$obj->canCreate()) return "";
  
  		$dbField = $this->getDataObjectField();
  
  		$textField = TextField::create(
  			"gridfieldaddbydbfield[" . $obj->ClassName . "][" . Convert::raw2htmlatt($dbField) . "]"
  			)->setAttribute("placeholder", $obj->fieldLabel($dbField))
  			->addExtraClass("no-change-track");
  
  		$addAction = new GridField_FormAction($gridField, 
  			'add',
  			_t('GridFieldAddByDBField.Add', 
  				"Add {name}", "Add button text", 
  				array("name" => $obj->i18n_singular_name())
  			), 
  			'add', 
  			'add'
  		);
  		$addAction->setAttribute('data-icon', 'add');
  
  		// Start thinking about rending this back to the GF
  		$forTemplate = new ArrayData(array());
  		$forTemplate->Fields = new ArrayList();
  
  		$forTemplate->Fields->push($textField);
  		$forTemplate->Fields->push($addAction);
  
  		return array(
  			$this->targetFragment => $forTemplate->renderWith("GridFieldAddByDBField")
  		);
  	}
docs: Renders the TextField and add button to the GridField.
  
  @param $girdField GridField
  
  @return string HTML