Add a document presenting general design considerations

Author: dunglas

core/design.md

@@ -0,0 +1,41 @@
+# General Design Considerations
+
+API Platform can be used [both as a "design-first" and "code-first"](https://swagger.io/blog/api-design/design-first-or-code-first-api-development/)
+API framework. However, the "design-first" approach is recommended: first you design the **public** shape of API endpoints.
+
+To do so, you write a plain old PHP object representing the input and output of your endpoint. This is the class that will
+be marked with the `@ApiResource` annotation.
+This class **doesn't have** to be mapped with Doctrine, or any other persistence system. It must be simple (usually just
+a data structure with no or minimal behaviors) and will be automatically to converted to a  [Hydra](extending-jsonld-context.md)
+and [OpenAPI / Swagger](swagger.md) documentation by API Platform (there is a 1-1 mapping between this object and those
+docs).
+
+Then, it's up to the developer to feed API Platform with an hydrated version of this API resource object by implementing
+the [`DataProviderInterface`](data-providers.md). Basically, the data provider will query the persistence system (RDBMS,
+document or graph DB, external API...), and must hydrate and return the POPO that has been designed in the first time.
+
+When updating a state (`POST`, `PUT`, `PATCH`, `DELETE` HTTP methods), it's up to the developer to persist properly the
+data provided by API Platform's resource object hydrated by the serializer to the persistence system. To do so, there is
+another interface to implement: [`DataPersisterInterface`](data-persisters.md). Here, is the reverse operation, this class
+will read the API Platform resource object, hydrate a DTO and trigger a command, populate and event store, or persist the
+data in any other useful way (it's not the responsibility of API Platform, it's up to the application developer).
+
+For [Rapid Application Development](https://en.wikipedia.org/wiki/Rapid_application_development), convenience and prototyping,
+**if and only if the class is marked with `@ApiResource` is also a Doctrine entity**, the developer can use the Doctrine
+ORM's data provider and data persister implementations shipped with API Platform.
+
+In this case, the public (`@ApiResource`) and internal (Doctrine entity) data model are shared. Then, API Platform will
+be able to query, filter, paginate and persist automatically data.
+This is approach is super-convenient and efficient, but is probably **not a good idea** for non-[CRUD](https://en.wikipedia.org/wiki/Create,_read,_update_and_delete)
+and/or large systems.
+It's up to the developers to use, or to not use those built-in data providers/persisters depending of the business they
+are dealing with. API Platform makes it easy to create custom data providers and persisters, and to implement appropriate patterns such as
+[CQS](https://www.martinfowler.com/bliki/CommandQuerySeparation.html) or [CQRS](https://martinfowler.com/bliki/CQRS.html).
+
+To create [Event Sourcing](https://martinfowler.com/eaaDev/EventSourcing.html)-based systems, a convenient approach is:
+
+* to persist data in an event store using a custom [data persister](data-persisters.md)
+* to create projections in standard RDBMS (Postgres, MariaDB...) tables or views
+* to map those projections with read-only Doctrine entity classes **and** to mark those classes with `@ApiResource`
+
+Then you can benefit of all built-in Doctrine filters, sorting, pagination, auto-joins, etc provided by API Platform.

index.md

@@ -12,16 +12,17 @@
     1.  [Installing API Platform Core](core/getting-started.md#installing-api-platform-core)
     2.  [Before Reading this Documentation](core/getting-started.md#before-reading-this-documentation)
     3.  [Mapping the Entities](core/getting-started.md#mapping-the-entities)
-3.  [Configuration](core/configuration.md)
-4.  [Operations](core/operations.md)
+3.  [General Design Considerations](core/design.md)
+4.  [Configuration](core/configuration.md)
+5.  [Operations](core/operations.md)
     1.  [Enabling and Disabling Operations](core/operations.md#enabling-and-disabling-operations)
     2.  [Configuring Operations](core/operations.md#configuring-operations)
     3.  [Subresources](core/operations.md#subresources)
     4.  [Creating Custom Operations and Controllers](core/operations.md#creating-custom-operations-and-controllers)
         1. [Recommended Method](core/operations.md#recommended-method)
         2. [Alternative Method](core/operations.md#alternative-method)
-5.  [Overriding Default Order](core/default-order.md)
-6.  [Filters](core/filters.md)
+6.  [Overriding Default Order](core/default-order.md)
+7.  [Filters](core/filters.md)
     1.  [Doctrine ORM Filters](core/filters.md#doctrine-orm-filters)
         1.  [Search Filter](core/filters.md#search-filter)
         2.  [Date Filter](core/filters.md#date-filter)
@@ -42,7 +43,7 @@
             1. [Using Doctrine Filters](core/filters.md#using-doctrine-filters)
         2.  [Overriding Extraction of Properties from the Request](core/filters.md#overriding-extraction-of-properties-from-the-request)
     4.  [ApiFilter Annotation](core/filters.md#apifilter-annotation)
-7.  [The Serialization Process](core/serialization.md)
+8.  [The Serialization Process](core/serialization.md)
     1.  [Overall Process](core/serialization.md#overall-process)
     2.  [Available Serializers](core/serialization.md#available-serializers)
     3.  [The Serialization Context, Groups and Relations](core/serialization.md#the-serialization-context-groups-and-relations)
@@ -58,35 +59,35 @@
     9.  [Decorating a Serializer and Add Extra Data](core/serialization.md#decorating-a-serializer-and-add-extra-data)
     10. [Entity Identifier Case](core/serialization.md#entity-identifier-case)
     11. [Embedding the JSON-LD Context](core/serialization.md#embedding-the-json-ld-context)
-8.  [Validation](core/validation.md)
+9.  [Validation](core/validation.md)
     1.  [Using Validation Groups](core/validation.md#using-validation-groups)
     2.  [Using Validation Groups on operations](core/validation.md#using-validation-groups-on-operations)
     3.  [Dynamic Validation Groups](core/validation.md#dynamic-validation-groups)
     4.  [Error Levels and Payload Serialization](core/validation.md#error-levels-and-payload-serialization)
-9.  [Error Handling](core/errors.md)
+10.  [Error Handling](core/errors.md)
     1.  [Converting PHP Exceptions to HTTP Errors](core/errors.md#converting-php-exceptions-to-http-errors)
-10.  [Pagination](core/pagination.md)
+11.  [Pagination](core/pagination.md)
     1.  [Disabling the Pagination](core/pagination.md#disabling-the-pagination)
     2.  [Changing the Number of Items per Page](core/pagination.md#changing-the-number-of-items-per-page)
     3.  [Partial Pagination](core/pagination.md#partial-pagination)
-11.  [The Event System](core/events.md)
-12. [Content Negotiation](core/content-negotiation.md)
+12.  [The Event System](core/events.md)
+13. [Content Negotiation](core/content-negotiation.md)
     1.  [Enabling Several Formats](core/content-negotiation.md#enabling-several-formats)
     2.  [Registering a Custom Serializer](core/content-negotiation.md#registering-a-custom-serializer)
     3.  [Creating a Responder](core/content-negotiation.md#creating-a-responder)
     4.  [Writing a Custom Normalizer](core/content-negotiation.md#writing-a-custom-normalizer)
-13. [Using External JSON-LD Vocabularies](core/external-vocabularies.md)
-14. [Extending JSON-LD context](core/extending-jsonld-context.md)
-15. [Data Providers](core/data-providers.md)
+14. [Using External JSON-LD Vocabularies](core/external-vocabularies.md)
+15. [Extending JSON-LD context](core/extending-jsonld-context.md)
+16. [Data Providers](core/data-providers.md)
     1.  [Custom Collection Data Provider](core/data-providers.md#custom-collection-data-provider)
     2.  [Custom Item Data Provider](core/data-providers.md#custom-item-data-provider)
     3.  [Injecting the Serializer in an `ItemDataProvider`](core/data-providers.md#injecting-the-serializer-in-an-itemdataprovider)
-16. [Data Persisters](core/data-persisters.md)
-17. [Extensions](core/extensions.md)
+17. [Data Persisters](core/data-persisters.md)
+18. [Extensions](core/extensions.md)
     1.  [Custom Extension](core/extensions.md#custom-extension)
     2.  [Filter upon the current user](core/extensions.md#example)
-18. [Security](core/security.md)
-19. [Performance](core/performance.md)
+19. [Security](core/security.md)
+20. [Performance](core/performance.md)
     1.  [Enabling the Built-in HTTP Cache Invalidation System](core/performance.md#enabling-the-builtin-http-cache-invalidation-system)
     2.  [Enabling the Metadata Cache](core/performance.md#enabling-the-metadata-cache)
     3.  [Using PPM (PHP-PM)](core/performance.md#using-ppm-php-pm)
@@ -98,32 +99,32 @@
             3.  [Override at Resource and Operation Level](core/performance.md#override-at-resource-and-operation-level)
             4.  [Disable Eager Loading](core/performance.md#disable-eager-loading)
         3.  [Partial Pagination](core/performance.md#partial-pagination)
-20. [Operation Path Naming](core/operation-path-naming.md)
+21. [Operation Path Naming](core/operation-path-naming.md)
     1.  [Configuration](core/operation-path-naming.md#configuration)
     2.  [Create a Custom Operation Path Naming](core/operation-path-naming.md#create-a-custom-operation-path-resolver)
         1.  [Defining the Operation Path Naming](core/operation-path-naming.md#defining-the-operation-path-resolver)
         2.  [Registering the Service](core/operation-path-naming.md#registering-the-service)
         3.  [Configure it](core/operation-path-naming.md#configure-it)
-21. [Accept application/x-www-form-urlencoded Form Data](core/form-data.md)
-22. [FOSUserBundle Integration](core/fosuser-bundle.md)
+22. [Accept application/x-www-form-urlencoded Form Data](core/form-data.md)
+23. [FOSUserBundle Integration](core/fosuser-bundle.md)
     1.  [Installing the Bundle](core/fosuser-bundle.md#installing-the-bundle)
     2.  [Enabling the Bridge](core/fosuser-bundle.md#enabling-the-bridge)
     3.  [Creating a `User` Entity with Serialization Groups](core/fosuser-bundle.md#creating-a-user-entity-with-serialization-groups)
-23. [Adding a JWT authentication using LexikJWTAuthenticationBundle](core/jwt.md)
+24. [Adding a JWT authentication using LexikJWTAuthenticationBundle](core/jwt.md)
     1. [Testing with Swagger](core/jwt.md#testing-with-swagger)
     2. [Testing with Behat](core/jwt.md#testing-with-behat)
-24. [NelmioApiDocBundle integration](core/nelmio-api-doc.md)
-25. [AngularJS Integration](core/angularjs-integration.md)
+25. [NelmioApiDocBundle integration](core/nelmio-api-doc.md)
+26. [AngularJS Integration](core/angularjs-integration.md)
     1.  [Restangular](core/angularjs-integration.md#restangular)
     2.  [ng-admin](core/angularjs-integration.md#ng-admin)
-26. [Swagger Support](core/swagger.md)
+27. [Swagger Support](core/swagger.md)
     1. [Override Swagger documentation](core/swagger.md#override-swagger-documentation)
-27. [GraphQL Support](core/graphql.md)
+28. [GraphQL Support](core/graphql.md)
     1. [Overall View](core/graphql.md#overall-view)
     2. [Enabling GraphQL](core/graphql.md#enabling-graphql)
     3. [GraphiQL](core/graphql.md#graphiql)
-28. [Handling Data Transfer Objects (DTOs)](core/dto.md)
-29. [Handling File Upload with VichUploaderBundle](core/file-upload.md)
+29. [Handling Data Transfer Objects (DTOs)](core/dto.md)
+30. [Handling File Upload with VichUploaderBundle](core/file-upload.md)
 
 ## The Schema Generator Component: Generate Data Models from Open Vocabularies