Package org.axonframework.modelling.entity

Class ConcreteEntityMetamodel<E>

java.lang.Object

org.axonframework.modelling.entity.ConcreteEntityMetamodel<E>

Type Parameters:

E - The type of the entity this metamodel describes.

All Implemented Interfaces:

DescribableComponent, EntityMetamodel<E>, EntityEvolver<E>

public class ConcreteEntityMetamodel<E>
extends Object
implements DescribableComponent, EntityMetamodel<E>

Implementation of the EntityMetamodel interface that enables the definition of command handlers and child entities for a given entity type E. Optionally, an EntityEvolver can be provided to evolve the entity state based on events. If no EntityEvolver is provided, state can exclusively be changed through command handlers.

During the handling of commands, handlers defined in child entities take precedence over the parent entity's command handlers. Event handlers are invoked on both the parent and child models, with child models being invoked first.

Since:

5.0.0

Author:

Mitchell Herrijgers

Method Summary

Modifier and Type	Method	Description
void	describeTo(ComponentDescriptor descriptor)	Describe the properties of this DescribableComponent with the given descriptor.
Class<E>	entityType()	Returns the Class of the entity this metamodel describes.
E	evolve(E entity, EventMessage event, ProcessingContext context)	Evolve the given entity by applying the given event to it.
static <E> EntityMetamodelBuilder<E>	forEntityClass(Class<E> entityType)	Creates a builder for the specified entity type.
MessageStream.Single<CommandResultMessage>	handleCreate(CommandMessage message, ProcessingContext context)	Handles the given CommandMessage as the creation of a new entity.
MessageStream.Single<CommandResultMessage>	handleInstance(CommandMessage message, E entity, ProcessingContext context)	Handles the given CommandMessage for the given entity.
Set<QualifiedName>	supportedCommands()	Returns the set of all QualifiedNames that this metamodel supports for command handlers, both creational and instance commands.
Set<QualifiedName>	supportedCreationalCommands()	Returns the set of all QualifiedNames that this metamodel supports for creating entities.
Set<QualifiedName>	supportedInstanceCommands()	Returns the set of all QualifiedNames that this metamodel supports for instance commands.
String	toString()

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Method Details

forEntityClass

@Nonnull
public static <E> EntityMetamodelBuilder<E> forEntityClass(@Nonnull
 Class<E> entityType)

Creates a builder for the specified entity type. This builder provides a fluent API for defining and constructing an EntityMetamodel for the given entity class, allowing the registration of command handlers, child entities, and an optional entity evolver.

Type Parameters:

E - The type of the entity for which the metamodel is being built.

Parameters:

entityType - The Class object representing the entity type.

Returns:

A ConcreteEntityMetamodel.Builder instance configured for the specified entity type.

supportedCommands

@Nonnull
public Set<QualifiedName> supportedCommands()

Description copied from interface: EntityMetamodel

Returns the set of all QualifiedNames that this metamodel supports for command handlers, both creational and instance commands. This is the union of the EntityMetamodel.supportedCreationalCommands() and EntityMetamodel.supportedInstanceCommands() methods.

Specified by:

supportedCommands in interface EntityMetamodel<E>

Returns:

A set of QualifiedName instances representing the supported command names.

supportedCreationalCommands

@Nonnull
public Set<QualifiedName> supportedCreationalCommands()

Description copied from interface: EntityMetamodel

Returns the set of all QualifiedNames that this metamodel supports for creating entities. These are the command types that can be used to create an entity of this type through the EntityMetamodel.handleCreate(org.axonframework.messaging.commandhandling.CommandMessage, org.axonframework.messaging.core.unitofwork.ProcessingContext) method.

Specified by:

supportedCreationalCommands in interface EntityMetamodel<E>

Returns:

A set of QualifiedName instances representing the supported command names.

supportedInstanceCommands

@Nonnull
public Set<QualifiedName> supportedInstanceCommands()

Description copied from interface: EntityMetamodel

Returns the set of all QualifiedNames that this metamodel supports for instance commands. These are the command types that can be used on entity instances of this type through the EntityMetamodel.handleInstance(org.axonframework.messaging.commandhandling.CommandMessage, E, org.axonframework.messaging.core.unitofwork.ProcessingContext) method.

Specified by:

supportedInstanceCommands in interface EntityMetamodel<E>

Returns:

A set of QualifiedName instances representing the supported command names.

handleCreate

@Nonnull
public MessageStream.Single<CommandResultMessage> handleCreate(@Nonnull
 CommandMessage message,
 @Nonnull
 ProcessingContext context)

Description copied from interface: EntityMetamodel

Handles the given CommandMessage as the creation of a new entity. It is up to the registered command handler to create the entity.

This method is used to handle commands for new entities. If you want to handle commands for existing entities, use the EntityMetamodel.handleInstance(org.axonframework.messaging.commandhandling.CommandMessage, E, org.axonframework.messaging.core.unitofwork.ProcessingContext) method instead. If the command handler is only known as an instance command handler and this method is called, it will result in a failed message stream.

Specified by:

handleCreate in interface EntityMetamodel<E>

Parameters:

message - The CommandMessage to handle.

context - The ProcessingContext for the command.

Returns:

A stream with a message containing the result of the command handling, which may be a CommandResultMessage or an error message.

handleInstance

@Nonnull
public MessageStream.Single<CommandResultMessage> handleInstance(@Nonnull
 CommandMessage message,
 @Nonnull
 E entity,
 @Nonnull
 ProcessingContext context)

Description copied from interface: EntityMetamodel

Handles the given CommandMessage for the given entity. If any of its children can handle the command, it will be delegated to them. Otherwise, the command will be handled by this metamodel. If the command is not handled by this metamodel or any of its children, an MessageStream.failed(Throwable) will be returned.

This method is used to handle commands for existing entities. If you want to handle commands for new entities, use the EntityMetamodel.handleCreate(org.axonframework.messaging.commandhandling.CommandMessage, org.axonframework.messaging.core.unitofwork.ProcessingContext) method instead. If the command handler is only known as a creational command handler and this method is called, it will result in a failed message stream.

Specified by:

handleInstance in interface EntityMetamodel<E>

Parameters:

message - The CommandMessage to handle.

entity - The entity instance to handle the command for.

context - The ProcessingContext for the command.

Returns:

A stream with a message containing the result of the command handling, which may be a CommandResultMessage or an error message.

evolve

@Nullable
public E evolve(@Nonnull
 E entity,
 @Nonnull
 EventMessage event,
 @Nonnull
 ProcessingContext context)

Description copied from interface: EntityEvolver

Evolve the given entity by applying the given event to it.

Specified by:

evolve in interface EntityEvolver<E>

Parameters:

entity - The current entity to evolve with the given event.

event - The event that might adjust the entity.

context - The context within which to evolve the entity by the given event.

Returns:

The evolved entity based on the given event, or the same entity when nothing happened.

entityType

@Nonnull
public Class<E> entityType()

Description copied from interface: EntityMetamodel

Returns the Class of the entity this metamodel describes.

Specified by:

entityType in interface EntityMetamodel<E>

Returns:

The Class of the entity this metamodel describes.

describeTo

public void describeTo(@Nonnull
 ComponentDescriptor descriptor)

Description copied from interface: DescribableComponent

Describe the properties of this DescribableComponent with the given descriptor.

Components should call the appropriate describeProperty methods on the descriptor to register their properties. The descriptor is responsible for determining how these properties are formatted and structured in the final output.

Best Practices: As a general rule, all relevant fields of a DescribableComponent implementation should be described in this method. However, developers have discretion to include only the fields that make sense in the context. Not every field may be meaningful for description purposes, especially internal implementation details. Furthermore, components might want to expose different information based on their current state. The final decision on what properties to include lies with the person implementing the describeTo method, who should focus on providing information that is useful for understanding the component's configuration and state.

Example implementation:

 public void describeTo(ComponentDescriptor descriptor) {
     descriptor.describeProperty("name", this.name);
     descriptor.describeProperty("enabled", this.enabled);
     descriptor.describeProperty("configuration", this.configuration); // A nested component
     descriptor.describeProperty("handlers", this.eventHandlers);      // A collection
 }
 

Specified by:

describeTo in interface DescribableComponent

Parameters:

descriptor - The component descriptor to describe this DescribableComponentn its properties in.

toString

public String toString()

Overrides:

toString in class Object