getPhpType example

$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)) {
                        return null;
                    }
                }
            }

            return [new Type(
                Type::BUILTIN_TYPE_OBJECT,
                false,
                Collection::class,
                true,
                new Type($collectionKeyType),