core-bundle/src/Resources/contao/library/Contao/Model/Collection.php
public function getRelated($strKey)
	{
		if ($this->intIndex < 0)
		{
			$this->first();
		}

		return $this->arrModels[$this->intIndex]->getRelated($strKey);
	}
public function getRelated($strKey)
	{
		if ($this->intIndex < 0)
		{
			$this->first();
		}

		return $this->arrModels[$this->intIndex]->getRelated($strKey);
	}
Lazy load related records

@param string $strKey The property name

@return Collection|Model The model or a model collection if there are multiple rows