protected function GroupRelatedRowsByParentKeys(array &$MappedRelatedRows, ForeignKey $ForeignKey, array $ParentRows, array $RelatedRows)
{
$ParentJoinTableKeys = $this->ParentForeignKey->GetParentColumns();
$ParentReferencedKeys = $this->ParentForeignKey->GetReferencedColumns();
$GroupedRelatedRows = $this->GroupRowsByColumnValues($RelatedRows, $ParentJoinTableKeys);
$this->MapParentRowKeysToGroupedRelatedRows($MappedRelatedRows, $ParentRows, $ParentReferencedKeys, $GroupedRelatedRows);
}