Entity::appendField

protected function appendField(Field $field)
{
	if (isset($this->fields[StringHelper::strtoupper($field->getName())]) && !$this->isClone)
	{
		trigger_error(sprintf(
			'Entity `%s` already has Field with name `%s`.', $this->getFullName(), $field->getName()
		), E_USER_WARNING);

		return false;
	}

	if ($field instanceof Reference)
	{
		// references cache
		$this->references[$field->getRefEntityName()][] = $field;
	}

	$this->fields[StringHelper::strtoupper($field->getName())] = $field;

	if ($field instanceof ScalarField && $field->isPrimary())
	{
		$this->primary[] = $field->getName();

		if($field->isAutocomplete())
		{
			$this->autoIncrement = $field->getName();
		}
	}

	// add reference field for UField iblock_section
	if ($field instanceof UField && $field->getTypeId() == 'iblock_section')
	{
		$refFieldName = $field->getName().'_BY';

		if ($field->isMultiple())
		{
			$localFieldName = $field->getValueFieldName();
		}
		else
		{
			$localFieldName = $field->getName();
		}

		$newFieldInfo = array(
			'data_type' => 'BitrixIblockSection',
			'reference' => array($localFieldName, 'ID')
		);

		$newRefField = new Reference($refFieldName, $newFieldInfo['data_type'], $newFieldInfo['reference'][0], $newFieldInfo['reference'][1]);
		$newRefField->setEntity($this);

		$this->fields[StringHelper::strtoupper($refFieldName)] = $newRefField;
	}

	return true;
}