org.axonframework.commandhandling.model

Interface Aggregate<T>

Type Parameters:

T - The aggregate root type

All Known Implementing Classes:

AnnotatedAggregate, EventSourcedAggregate, LockAwareAggregate

public interface Aggregate<T>

Interface that describes an aggregate. An aggregate is an isolated tree of entities that is capable of handling commands. Implementations of this interface defer the actual handling of commands to a wrapped instance of type T or one of its entities.

When a command is dispatched to an aggregate Axon will load the aggregate instance and invoke the related command handler method. It is rarely necessary to interact with aggregates directly. Though it is not recommended it is possible to invoke methods on the wrapped instance using invoke(Function) and execute(Consumer).

Method Summary

Modifier and Type	Method and Description
void	execute(Consumer<T> invocation) Execute a method on the underlying aggregate or one of its instances.
Object	handle(CommandMessage<?> commandMessage) Handle the given commandMessage on the aggregate root or one of its child entities.
Object	identifier() Get the unique identifier of this aggregate
default String	identifierAsString() Get the unique identifier of this aggregate, represented as a String.
<R> R	invoke(Function<T,R> invocation) Invoke a method on the underlying aggregate root or one of its instances.
boolean	isDeleted() Check if this aggregate has been deleted.
Class<? extends T>	rootType() Get the class type of the wrapped aggregate root that the Aggregate defers to for command handling.
String	type() Get the String representation of the aggregate's type.
Long	version() Get the aggregate's version.

Method Detail

type

String type()

Get the String representation of the aggregate's type. This defaults to the simple name of the rootType() unless configured otherwise.

Returns:

The aggregate's type

identifierAsString

default String identifierAsString()

Get the unique identifier of this aggregate, represented as a String.

Returns:

The aggregate's identifier as a String

identifier

Object identifier()

Get the unique identifier of this aggregate

Returns:

The aggregate's identifier

version

Long version()

Get the aggregate's version. For event sourced aggregates this is identical to the sequence number of the last applied event.

Returns:

The aggregate's version

handle

Object handle(CommandMessage<?> commandMessage)
       throws Exception

Handle the given commandMessage on the aggregate root or one of its child entities.

Parameters:

commandMessage - The command to be handled by the aggregate

Returns:

The result of command handling. Returns null in case the command yields no result.

Throws:

Exception - in case one is triggered during command processing

invoke

<R> R invoke(Function<T,R> invocation)

Invoke a method on the underlying aggregate root or one of its instances. Use this over execute(Consumer) to obtain an invocation result, for instance in order to query the aggregate.

Note that the use of this method is not recommended as aggregates are not meant to be queried. Relying on this method is commonly a sign of design smell.

Type Parameters:

R - The type of the result produced by the given invocation

Parameters:

invocation - The function that performs the actual invocation

Returns:

The invocation result

execute

void execute(Consumer<T> invocation)

Execute a method on the underlying aggregate or one of its instances.

Note that the use of this method is not recommended as the wrapped aggregate instance is not meant to be exposed. Relying on this method is commonly a sign of design smell.

Parameters:

invocation - The function that performs the invocation

isDeleted

boolean isDeleted()

Check if this aggregate has been deleted. This is checked by aggregate repositories when an aggregate is loaded. In case the repository is asked to load a deleted aggregate the repository will refuse by throwing an AggregateDeletedException.

Returns:

true in case the aggregate was deleted, false otherwise

rootType

Class<? extends T> rootType()

Get the class type of the wrapped aggregate root that the Aggregate defers to for command handling.

Returns:

The aggregate root type