@SagaEventHandler
methods. Unlike regular event handlers, multiple instances of a saga may exist at any time. Sagas are managed by a single event processor (Tracking or Subscribing), which is dedicated to dealing with events for that specific saga type.@SagaEventHandler
. If a specific event signifies the start of a transaction, add another annotation to that same method: @StartSaga
. This annotation will create a new saga and invoke its event handler method when a matching event is published.forceNew
property on the @StartSaga
annotation to true
.@EndSaga
. The saga its life cycle will be ended after the invocation of the handler. Alternatively, you can call SagaLifecycle.end()
from inside the saga to end the life cycle. This allows you to conditionally end the saga.AssociationValue
s. An AssociationValue
consists of a key and a value. The key represents the type of identifier used, for example "orderId" or "order". The value represents the corresponding value, "1" or "2" in the previous example.@SagaEventHandler
annotated methods are evaluated is identical to that of @EventHandler
methods (see Annotated event handler). A method matches if the parameters of the handler method match the incoming event, and if the saga has an association with the property defined on the handler method.@SagaEventHandler
annotation has two attributes, of which associationProperty
is the most important one. This is the name of the property on the incoming event that should be used to find associated sagas. The key of the association value is the name of the property. The value is the value returned by property its getter method.String getOrderId()
, which returns "123". If a method accepting this event is annotated with @SagaEventHandler(associationProperty="orderId")
, this Event is routed to all Sagas that have been associated with an AssociationValue
with key "orderId" and value "123". This may either be exactly one, more than one, or even none at all.keyName
in the @SagaEventHandler
annotation. It would then become @SagaEventHandler(associationProperty="sellOrderId", keyName="orderId")
ResourceInjector
. It is used by the SagaRepository
to inject resources into a saga. Axon provides a SpringResourceInjector
, which injects annotated fields and methods with resources from the Application Context. Axon also provides a SimpleResourceInjector
, which injects resources that have been registered with it into @Inject
annotated methods and fields.TipSince resources should not be persisted with the saga, make sure to add thetransient
keyword to those fields. This will prevent the serialization mechanism to attempt to write the contents of these fields to the repository. The repository will automatically re-inject the required resources after a saga has been deserialized.
SimpleResourceInjector
allows for a pre-specified collection of resources to be injected. It scans the (setter) methods and fields of a Saga to find ones that are annotated with @Inject
.ConfigurationResourceInjector
. It will inject any resource available in the configuration. Components like the EventBus
, EventStore
, CommandBus
and CommandGateway
are available by default. You can also register your own components using configurer.registerComponent()
.SpringResourceInjector
uses Spring's dependency injection mechanism to inject resources into a Saga. This means you can use setter injection or direct field injection if you require. The method or field to be injected needs to be annotated in order for Spring to recognize it as a dependency, for example with @Autowired
.SagaManager
and the SagaRepository
.AnnotatedSagaManager
, which is provided to an Event Processor to perform the actual invocation of handlers. It is initialized using the type of the Saga to manage, as well as a SagaRepository
where Sagas of that type can be stored and retrieved. A single AnnotatedSagaManager
can only manage a single Saga type.SagaRepository
is responsible for storing and retrieving sagas, for use by the SagaManager
. It is capable of retrieving specific saga instances by their identifier as well as by their association values.AnnotatedSagaRepository
implementation, which allows the lookup of saga instances while guaranteeing that only a single instance of the saga may be accessed at the same time. It uses a SagaStore
to perform the actual persistence of saga instances.JdbcSagaStore
, InMemorySagaStore
, JpaSagaStore
and MongoSagaStore
.CachingSagaStore
which wraps another implementation to add caching behavior. Note that the CachingSagaStore
is a write-through cache, which means save operations are always immediately forwarded to the backing Store, to ensure data safety.JpaSagaStore
uses JPA to store the state and association values of sagas. Sagas themselves do not need any JPA annotations; Axon will serialize the sagas using a Serializer
(similar to event serialization, you can choose between an XStreamSerializer
or JacksonSerializer
, which can be set by configuring the default Serializer
in your application. For more details, see Serializers.JpaSagaStore
is configured with an EntityManagerProvider
, which provides access to an EntityManager
instance to use. This abstraction allows for the use of both application managed and container managed EntityManager
s. Optionally, you can define the serializer to serialize the Saga instances with. Axon defaults to the XStreamSerializer
.JdbcSagaStore
uses plain JDBC to store stage instances and their association values. Similar to the JpaSagaStore
, saga instances do not need to be aware of how they are stored. They are serialized using a serializer.JdbcSagaStore
is initialized with either a DataSource
or a ConnectionProvider
. While not required, when initializing with a ConnectionProvider
, it is recommended to wrap the implementation in a UnitOfWorkAwareConnectionProviderWrapper
. It will check the current Unit of Work for an already open database connection, to ensure that all activity within a unit of work is done on a single connection.JdbcSagaRepository
uses plain SQL statements to store and retrieve information. This may mean that some operations depend on the database specific SQL dialect. It may also be the case that certain database vendors provide non-standard features that you would like to use. To allow for this, you can provide your own SagaSqlSchema
. The SagaSqlSchema
is an interface that defines all the operations the repository needs to perform on the underlying database. It allows you to customize the SQL statement executed for each operation. The default is the GenericSagaSqlSchema
. Other implementations available are PostgresSagaSqlSchema
, Oracle11SagaSqlSchema
and HsqlSagaSchema
.MongoSagaStore
stores the saga instances and their associations in a MongoDB database. The MongoSagaStore
stores all sagas in a single collection in a MongoDB database. For each saga instance, a single document is created.MongoSagaStore
also ensures that at any time, only a single Saga instance exists for any unique Saga in a single JVM. This ensures that no state changes are lost due to concurrency issues.MongoSagaStore
is initialized using a MongoTemplate
and optionally a Serializer
. The MongoTemplate
provides a reference to the collection to store the sagas in. Axon provides the DefaultMongoTemplate
, which takes a MongoClient
instance as well as the database name and name of the collection to store the sagas in. The database name and collection name may be omitted. In that case, they default to "axonframework"
and "sagas"
, respectively.CachingSagaStore
implementation. It is a SagaStore
that wraps another one, which does the actual storage. When loading sagas or association values, the CachingSagaStore
will first consult its caches, before delegating to the wrapped repository. When storing information, all calls are always delegated to ensure that the backing storage always has a consistent view on the saga's state.SagaStore
in a CachingSagaStore
. The constructor of the CachingSagaStore
takes three parameters: 1. The SagaStore
to wrap 2. The cache to use for association values 3. The cache to use for saga instancesDefault Saga Processor nameAs a Saga is a type of event handler, it is part of an Event Processor. Without defining any assignment rules, a Saga's processor name equals the Saga name appended with "Processor",With a Saga calledMySaga
, that would mean the processor is calledMySagaProcessor
.
SagaConfigurer
to construct the Saga, Saga Manager, Saga Repository and Saga Store. A default configuration for a Saga called MySaga
would look as follows:EventProcessingConfigurer
:@Saga
to auto-configure it:SagaStore
to use. The SagaStore
represents the mechanism that 'physically' stores the Saga instances, for which it uses the AnnotatedSagaRepository
(the default) to store and retrieve Saga instances. If no SagaStore
is configured Axon defaults an InMemorySagaStore
, thus not persisting the Saga on shutdown. To configure a SagaStore
for MySaga
consider the following snippet:SagaStore
, the SagaConfigurer
should be used through the EventProcessingConfigurer#registerSaga(Class<T>, Consumer<SagaConfigurer<T>>)
method:EventProcessingConfigurer#registerSagaStore(Function<Configuration, SagaStore>)
method.JpaSagaStore
or JdbcSagaStore
respectively. To provide a custom SagaStore
, providing a bean to the application context and defining the bean name on the @Saga
annotation suffices: