becklyn / ddd-core
DDD framework for PHP
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Requires
- php: >=8.0
- becklyn/utilities: ^2.0
- illuminate/collections: ^8.12 || ^9.0
- ramsey/uuid: ^4.0
- webmozart/assert: ^1.9
Requires (Dev)
- phpspec/prophecy-phpunit: ^2.0
- phpunit/phpunit: ^9.1
README
becklyn/ddd-core is a set of components for developing software with domain-driven design, event sourcing and CQRS. Support is included for:
- entity identity
- domain events and their handling
- event store and event sourcing
- transaction handling
- command handling
The components are designed to facilitate the following workflow:
- A command is dispatched through a command bus
- This initiates a transaction where a command handler processes the command and performs the desired action on an aggregate or executes a domain service
- If an unhandled exception occurs, the transaction is rolled back and all changes are discarded
- Otherwise, the transaction is committed, events raised by the aggregate or domain service are collected, persisted to the event store, and dispatched through an event bus
- Event subscribers listen to the events and dispatch new commands if other aggregates need to be modified in response, or if other kinds of actions need to be undertaken
- This repeats the "core transaction loop" until all events are resolved and no new commands are initiated, or in other words until eventual consistency is achieved.
Usage
becklyn/ddd-core provides the components mostly as abstract classes and interfaces to facilitate use independent of any specific technological infrastructure. Our choice is Symfony with Doctrine and SimpleBus, and we provide implementations tying everything together in the becklyn/ddd-doctrine-bridge and becklyn/ddd-symfony-bridge libraries. If you wish to use other technologies, you will need to provide your own implementations for the event store and event, transaction and command handling.
Core Loop
Here's a more detailed explanation on how to achieve the becklyn/ddd-core workflow:
- Dispatch a command via the
CommandBus
. Commands are plain PHP classes of your own creation, essentially DTOs, and they should contain all the data necessary to perform the desired action. At a minimum, they should contain the identity of the aggregate being manipulated. - The
CommandBus
should route the command to its corresponding handler. The implementation provided by becklyn/ddd-symfony-bridge does this automatically within a properly configured Symfony application. Otherwise, you will have to ensure this yourself. - Process the command in a handler extending the abstract
CommandHandler
class:- Each command class must have exactly one handler class.
- Your handler should have a public method accepting the command as its argument, and the method should call
CommandHandler::handleCommand
. handleCommand
will in turn call the abstractexecute
method in which you should implement your command handling logic:- Load an aggregate implementing the
EventProvider
interface (we recommend doing so from a repository). - Perform an action on the aggregate, raising domain events within it (you can use the
EventProviderCapabilities
orEventSourcedProviderCapabilities
trait in the aggregate to facilitate this). - Return the aggregate fom the
execute
method.
- Load an aggregate implementing the
CommandHandler
will dequeue any events raised by the aggregate returned fromexecute
, register them with theEventRegistry
and commit the transaction through theTransactionManager
.- Alternatively, a domain service may be called from
execute
. In such cases, the service should use theEventRegistry
to dequeue and register any events raised by the affected aggregate, andCommandHandler::execute
should return null.
TransactionManager::commit
should take care of any persistence concerns and callEventManager::flush
. Similarly,TransactionManager::rollback
should discard and changes and callEventManager::clear
. A Doctrine implementation is provided by becklyn/ddd-doctrine-bridge.- Flushing the
EventManager
collects all events registered by theEventRegistry
and dispatches them through theEventBus
. Clearing theEventManager
simply discards all events. - The
EventBus
should dispatch the events to any subscribers subscribing to them. becklyn/ddd-symfony-bridge provides a Symfony/SimpleBus implementation that does this automatically within a properly configured Symfony application. - If any other aggregates need to react to changes made to the initial aggregate, subscribe to the relevant events through event subscribers:
- Multiple subscribers may subscribe to any single event. It is not recommended that subscribers depend on the order in which they process events, nor that a subscriber should stop the propagation of an event. While we enforce these practices in becklyn/ddd-symfony-bridge, we do not impose any restrictions on your own implementations.
- The subscribers shouldn't contain any domain logic, but should instead generally only dispatch new commands.
Entities, Aggregates and Events
Entities must implement the EventProvider
interface, and they must raise a domain event for every change to their state. The EventProviderCapabilities
can be used by entities to facilitate this. Each entity must also have its corresponding identity class implementing the EntityId
interface. AbstractEntityId
is provided for a default implementation.
One entity in every aggregate serves as the aggregate root. Any and all interaction with the aggregate is allowed only through this entity, and thus only aggregate roots should have repositories. Aggregate root identities must implement the AggregateId
interface instead of just EntityId
. AbstractAggregateId
is provided for a default implementation. When dequeueEvents
is called on an aggregate root, it should in turn collect all of the events from other entities in the aggregate and return them along the events raised by the aggregate root.
Events must implement the DomainEvent
interface and may do so extending the AbstractDomainEvent
class. A domain event records a state change and must contain all the data necesary for it to be replayed from the previous state.
If using event sourcing, aggregates should use the EventSourcedProviderCapabilities
trait instead of EventProviderCapabilities
. While it is possible to implement repositories using the EventStore
and its getAggregateStream
method directly, this will likely result in low performance for most implementations if a large number of aggregates is fetched at once. For such scenarios we recommend using projections instead.
Testing
We write our PHPUnit/Prophecy unit tests inspired by the BDD workflow of "given/when/then". To test the code interacting with components from this library, we have gathered various given/when/then helper methods into traits. You can find them within the Testing namespaces of individual subdomans present in the library, for example:
Becklyn\Ddd\Commands\Testing\CommandHandlerTestTrait
Becklyn\Ddd\Events\Testing\DomainEventTestTrait