getSingleAssociationReferencedJoinColumnName example

// Check if indexBy value is a property                     $fieldName = $associationMapping['indexBy'];
                    if (null === ($typeOfField = $subMetadata->getTypeOfField($fieldName))) {
                        $fieldName = $subMetadata->getFieldForColumn($associationMapping['indexBy']);
                        // Not a property, maybe a column name?                         if (null === ($typeOfField = $subMetadata->getTypeOfField($fieldName))) {
                            // Maybe the column name is the association join column?                             $associationMapping = $subMetadata->getAssociationMapping($fieldName);

                            /** @var ClassMetadataInfo $subMetadata */
                            $indexProperty = $subMetadata->getSingleAssociationReferencedJoinColumnName($fieldName);
                            $subMetadata = $this->entityManager->getClassMetadata($associationMapping['targetEntity']);

                            // Not a property, maybe a column name?                             if (null === ($typeOfField = $subMetadata->getTypeOfField($indexProperty))) {
                                $fieldName = $subMetadata->getFieldForColumn($indexProperty);
                                $typeOfField = $subMetadata->getTypeOfField($fieldName);
                            }
                        }
                    }

                    if (!$collectionKeyType = $this->getPhpType($typeOfField)) {