SagaTopic
SagaTopic is where all topics and their metadata is defined in the orchestration service which are involved to overcome the long-running transaction. for instance if you have an PlaceOrderAggregator, In parallel with that you have to create a custom SagaTopic called PlaceOrderTopic for storing all the topics that used while entire place-order long-running transaction. that defined PlaceOrderTopic is used in the SagaEventNavigator for navigating the transaction’s spans.
The topic names should be identical to the Stacksaga kafka endpoints that are define in the target-services by using stacksaga-kafka-client.
as per the classification, you can define 5 topic types(SagaTopicType).
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COMMAND_DO_ACTION: The topics that are triggered for make some changes in the target database’s state. it should have a compensation to undo the changes that has been done in case of feature failure. -
QUERY_DO_ACTION: The topics that are triggered for retreating the data without any state change of the target service. -
COMMAND_UNDO_ACTION: The compensation action of theCOMMAND_DO_ACTION. it is the main default compensation. -
COMMAND_UNDO_BEFORE_ACTION: In addition to the default compensation(COMMAND_UNDO_ACTION), if there should have some additional more actions should be done before the default compensation of theCOMMAND_DO_ACTION, you can create the `COMMAND_UNDO_BEFORE_ACTION`s. -
COMMAND_UNDO_AFTER_ACTION: In addition to the default compensation(COMMAND_UNDO_ACTION), if there should have some additional more actions should be done after the default compensation of theCOMMAND_DO_ACTION, you can create the `COMMAND_UNDO_AFTER_ACTION`s.
The below diagram shows how the SagaTopic interacts with other components of the stacksaga-kafka flow.
(1)
public enum PlaceOrderTopic implements SagaTopic<PlaceOrderTopic> { (2)
DO_USER_VALIDATE(1, "user-service", SagaTopicType.QUERY_DO_ACTION),
DO_MAKE_PAYMENT(1, "order-service", SagaTopicType.COMMAND_DO_ACTION),
UNDO_MAKE_PAYMENT(2, "order-service", SagaTopicType.COMMAND_UNDO_ACTION, DO_MAKE_PAYMENT),
UNDO_MAKE_PAYMENT_SUB_BEFORE_1(-2.1f, "order-service", SagaTopicType.COMMAND_UNDO_BEFORE_ACTION, UNDO_MAKE_PAYMENT),
UNDO_MAKE_PAYMENT_SUB_BEFORE_2(-2.2f, "order-service", SagaTopicType.COMMAND_UNDO_BEFORE_ACTION, UNDO_MAKE_PAYMENT),
UNDO_MAKE_PAYMENT_SUB_AFTER_1(2.1f, "order-service", SagaTopicType.COMMAND_UNDO_AFTER_ACTION, UNDO_MAKE_PAYMENT),
DO_UPDATE_STOCK(3, "order-service", SagaTopicType.COMMAND_DO_ACTION),
UNDO_UPDATE_STOCK(4, "order-service", SagaTopicType.COMMAND_UNDO_ACTION, DO_UPDATE_STOCK),
DO_MAKE_DELIVERY(5, "delivery-service", SagaTopicType.COMMAND_DO_ACTION),
UNDO_MAKE_DELIVERY(6, "delivery-service", SagaTopicType.COMMAND_UNDO_ACTION, DO_MAKE_DELIVERY),
;
(3)
private final String targetServiceName;
(3)
private final SagaTopicType sagaEventType;
(3)
private final PlaceOrderTopic parent;
(3)
private final float topicKey;
(4)
//for initializing primary-execution topics
PlaceOrderTopic(float topicKey, String targetServiceName, SagaTopicType sagaEventType) {
this.targetServiceName = targetServiceName;
this.sagaEventType = sagaEventType;
this.parent = null; //parent is assigned as null due to the primary-execution topic has no any parent
this.topicKey = topicKey;
}
(4)
//for initializing revert-execution topics
PlaceOrderTopic(float topicKey, String targetServiceName, SagaTopicType sagaEventType, PlaceOrderTopic parent) {
this.targetServiceName = targetServiceName;
this.sagaEventType = sagaEventType;
this.parent = parent; //due to revert-execution topics are initialized with this constructor, the parent is assigned.
this.topicKey = topicKey;
}
(2)
@Override
public String targetService() {
(5)
return this.targetServiceName;
}
(2)
@Override
public SagaTopicType topicType() {
(5)
return this.sagaEventType;
}
(2)
@Override
public PlaceOrderTopic parent() {
(5)
return this.parent;
}
(2)
@Override
public float topicKey() {
(5)
return this.topicKey;
}
}| 1 | create a custom enum with desired name for SagaTopic. |
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| 2 | implements the enm from SagaTopic interface passing the same enum as the generic type parameter and @Override the required methods like targetService(), topicType(), parent(), topicKey(). |
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| 3 | create the following fields as final.
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| 4 | create two different constructors with the following parameters.
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| 5 | Returns the respective initialized data in the respective methods. those are accessed by the framework. |