Flat Mapper Bundle

This bundle aims to solve the problem of building nested DTOs from flat arrays (such as database queries results).

One of its purposes is to help you create DTOs the same way you would with the Doctrine NEW keyword, except at depth. Other ways to do that generally imply mapping entities to DTOs which is less performant (memory and CPU wise). You can find benchmarks for this package at Pixelshaped/flat-mapper-benchmark.

You can also use it to map SQL queries to objects, it has no dependency on a particular ORM.

How to use?

At a glance

Given a DTO such as AuthorDTO

$result = $flatMapper->map(AuthorDTO::class, $authorRepository->getAuthorsAndTheirBooks());

Will give you an array of AuthorDTO hydrated with all their BookDTO books (See complete example).

Installation

composer require pixelshaped/flat-mapper-bundle

Configuration

This bundle can work without any configuration, but will display better performance if mapping validation is disabled and some cache service is autowired.

If you use Symfony, you can create a configuration file to do so:

# config/pixelshaped_flat_mapper.yaml
pixelshaped_flat_mapper:
    validate_mapping: '%kernel.debug%' # disable on prod environment
    cache_service: cache.app

If you don't, you can still benefit from this when instantiating FlatMapper, i.e.:

$flatMapper = (new FlatMapper())
    ->setCacheService($yourCacheService) // PSR-6
    ->setValidateMapping(false)
;

Mapping pre-caching

The mapping for a DTO is created the first time the function is called. Subsequent calls during the same script execution won't recreate the mapping. If a cache service is configured, mapping will be loaded from the cache for next script executions.

If you want to cache all your DTOs in advance to avoid doing it on your hotpaths, you can do:

$dtoClassNames = [CustomerDTO::class, ...];
foreach($dtoClassNames as $className) {
    $flatMapper->createMapping($className);
}

This should be regarded as optional. Mapping information be created in any case when calling:

$flatMapper->map(CustomerDTO::class, $results);

Add mapping to your DTOs

This bundle comes with several attributes that you can use to add mapping to your DTOs:

• #[Identifier]: Any DTO has to have exactly one identifier. This identifier is used internally to keep track of the DTO instances and to create them only once. You can:
  • Use it as a Class attribute if you don't intend to use the property yourself (see example). It will then only be used internally and not be mapped to your DTO.
  • Use it as a Property attribute if you have some use for it (see example).
  • Specify the mapped property name directly on the attribute (see example). This is mandatory when used as a Class attribute.
  • Specify the mapped property name separately with the InboundProperty attribute, Doctrine-style (see example).
• #[Scalar("mapped_property_name")]: The column mapped_property_name of your result set will be mapped to a scalar property of your DTO (the value of the first row will be used). This is optional if your DTO's property names are already matching the result set (see example).
• #[ReferenceArray(NestedDTO::class)]: An array of NestedDTO will be created using the mapping information contained in NestedDTO.
• #[ScalarArray("mapped_property_name")] The column mapped_property_name of your result set will be mapped as an array of scalar properties, such as IDs (see example).

Hydrating nested DTOs

Given:

• AuthorDTO
• BookDTO

Calling FlatMapper with the following result set:

$results = [
    ['author_id' => 1, 'author_name' => 'Alice Brian', 'book_id' => 1, 'book_name' => 'Travelling as a group', 'book_publisher_name' => 'TravelBooks'],
    ['author_id' => 1, 'author_name' => 'Alice Brian', 'book_id' => 2, 'book_name' => 'My journeys', 'book_publisher_name' => 'Lorem Press'],
    ['author_id' => 1, 'author_name' => 'Alice Brian', 'book_id' => 3, 'book_name' => 'Coding on the road', 'book_publisher_name' => 'Ipsum Books'],
    ['author_id' => 2, 'author_name' => 'Bob Schmo', 'book_id' => 1, 'book_name' => 'Travelling as a group', 'book_publisher_name' => 'TravelBooks'],
    ['author_id' => 2, 'author_name' => 'Bob Schmo', 'book_id' => 4, 'book_name' => 'My best recipes', 'book_publisher_name' => 'Cooking and Stuff'],
];

$flatMapper->map(AuthorDTO::class, $results);

Will output:

Array
(
    [1] => AuthorDTO Object
        (
            [id] => 1
            [name] => Alice Brian
            [leafs] => Array
                (
                    [1] => BookDTO Object
                        (
                            [id] => 1
                            [name] => "Travelling as a group"
                            [publisherName] => "TravelBooks"
                        )
                    [2] => BookDTO Object
                        (
                            [id] => 2
                            [name] => "My journeys"
                            [publisherName] => "Lorem Press"
                        )
                    [3] => BookDTO Object
                        (
                            [id] => 3
                            [name] => "Coding on the road"
                            [publisherName] => "Ipsum Books"
                        )
                )
        )
    [2] => AuthorDTO Object
        (
            [id] => 2
            [name] => Bob Schmo
            [leafs] => Array
                (
                    [1] => BookDTO Object
                        (
                            [id] => 1
                            [name] => "Travelling as a group"
                            [publisherName] => "TravelBooks"
                        )
                    [4] => BookDTO Object
                        (
                            [id] => 4
                            [name] => "My best recipes"
                            [publisherName] => "Cooking and Stuff"
                        )
                )
        )
)

Hydrating Column Arrays

Given ScalarArrayDTO

Calling FlatMapper with the following result set:

$results = [
    ['object1_id' => 1, 'object1_name' => 'Root 1', 'object2_id' => 1],
    ['object1_id' => 1, 'object1_name' => 'Root 1', 'object2_id' => 2],
    ['object1_id' => 1, 'object1_name' => 'Root 1', 'object2_id' => 3],
    ['object1_id' => 2, 'object1_name' => 'Root 2', 'object2_id' => 1],
    ['object1_id' => 2, 'object1_name' => 'Root 2', 'object2_id' => 4],
];

Will output:

Array
(
    [1] => ScalarArrayDTO Object
        (
            [id] => 1
            [name] => Root 1
            [object2s] => Array
                (
                    [0] => 1
                    [1] => 2
                    [2] => 3
                )
        )
    [2] => ScalarArrayDTO Object
        (
            [id] => 2
            [name] => Root 2
            [object2s] => Array
                (
                    [0] => 1
                    [1] => 4
                )
        )
)

Working with Doctrine Queries

Given the following DTO class:

<?php
class CustomerDTO
{
    public function __construct(
        #[Identifier]
        #[Scalar('customer_id')]
        public int $id,
        #[Scalar('customer_name')]
        public string $name,
        #[ScalarArray('shopping_list_id')]
        public array $shoppingListIds
    )
}

The query:

<?php
$result = $this->getOrCreateQueryBuilder()
    ->select('customer.id AS customer_id, customer.name AS customer_name, shopping_list.id AS shopping_list_id')
    ->leftJoin('customer.shopping_list', 'shopping_list')
    ->getQuery()->getResult()
    ;

$flatMapper = new \Pixelshaped\FlatMapperBundle\FlatMapper()

$flatMapper->map(CustomerDTO::class, $result);

Will give you an array of CustomerDTO, with the $shoppingListIds property populated with an array of corresponding ShoppingList IDs.

Working with pagination

You can still use Doctrine to paginate your DQL query:

$qb = $customerRepository->createQueryBuilder('customer');
$qb
    ->leftJoin('customer.addresses', 'customer_addresses')
    ->select('customer.id AS customer_id, customer.ref AS customer_ref, customer_addresses.id AS address_id')
    ->setFirstResult(0)
    ->setMaxResults(10)
    ;

$paginator = new Paginator($qb->getQuery(), fetchJoinCollection: true);
$paginator->setUseOutputWalkers(false);

$result = $flatMapper->map(CustomerWithAddressesDTO::class, $paginator);

Will get you an array of 10 CustomerWithAddressesDTO (granted you do have 10 in your db).

Usage without Symfony

You can use this package without Symfony. Just instantiate the FlatMapper class and use its methods.

Alternatives

Doctrine provides a solution to build DTOs directly from a QueryBuilder:

Given a DTO class such as CustomerDTO:

<?php
class CustomerDTO
{
    public function __construct($name, $email, $city, $value = null){ /* ... */ }
}

Doctrine can execute a query that produces an array array<CustomerDTO>:

<?php
$query = $em->createQuery('SELECT NEW CustomerDTO(c.name, e.email, a.city) FROM Customer c JOIN c.email e JOIN c.address a');
$users = $query->getResult(); // array<CustomerDTO>

Unfortunately, if you need to retrieve DTOs with non-scalar properties, such as:

• an array of IDs
• an array of nested DTOs

then, the solution provided by Doctrine doesn't work. The creation of this bundle arose from that situation.

When I started coding this, I looked for alternatives but found only partial ones:

• mark-gerarts/automapper-plus is great at mapping objects to other objects (namely, entities to DTOs and vice versa), but doesn't solve the problem of mapping denormalized data (i.e. an array with the information for several objects on each row and a lot of redundancy between rows) to objects.
• jolicode/automapper is a great alternative to the previous bundle with the same limitations.
• sunrise-php/hydrator can map arrays to objects, but not denormalized arrays
• Several other bundles can map JSON info to objects.
• doctrine/orm solves this problem internally using ResultSetMapping. It can join on Entities but can't for DTOs because there's no way do declare a mapping for a DTO. That's actually why Doctrine only handles DTOs with scalar properties.
• You can technically build PARTIAL objects with Doctrine, but I consider this to be a bad practice as the next developer has no idea if the object at hand is a complete one or not. You could then map it to a DTO and discard it to avoid this situation, but the algorithmic complexity will likely be higher than the mapping we do with our bundle (O(n)).

Do not hesitate to suggest alternatives or to contribute.