SagaTemplate<A>

SagaTemplate is the class which is responsible for starting the StackSaga engine to invoke your transaction. By providing the necessary data, you can say to start the process of the transaction for StackSaga engine. SagaTemplate is an instance, and it provides one method called process(…) for starting the process.

SagaTemplate Is a spring bean that you can Autowire (Injectable) in Spring environment. You can autowire it by using spring @Autowire annotation or by creating the constructor.

@RestController
@RequestMapping("/order")
@AllArgsConstructor
public class PlaceOrderSagaController {

    private final SagaTemplate<PlaceOrderAggregator> sagaTemplate; (1)

    @PostMapping
    @ResponseStatus(HttpStatus.ACCEPTED)
    public Map<String, String> placeOrder() {
        (2)
        PlaceOrderAggregator aggregator = new PlaceOrderAggregator();
        aggregator.setUsername("mafei");
        aggregator.setTotal(200.00);

        (3)
        this.sagaTemplate.process(
                aggregator,
                CheckUserExecutor.class
        );
        (4)
        return Collections.singletonMap(
                "order_id",
                aggregator.getAggregatorTransactionId()
        );
    }
}

1	Autowire(inject) the `SagaTemplate` by providing the target Aggregator Class.
2	Initialize your aggregator by providing the initial data.
3	Use the autowired `SagaTemplate` object and call the `process(..)` method. As the first argument, you have to provide the initialized target aggregator object. As the second argument you have to provide, which is the first executor that should be started the transaction. According to the example, The 1st executor is `CheckUserExecutor.class`. It can be either Command-Executor or Query-Executor.
4	Returns the response by obtaining the aggregatorTransactionId from the initialized object.

Due to the fact that the target aggregator class has been extended from the Aggregator, you can use inherited methods from Aggregator class. The getAggregatorTransactionId() method is one of inherited methods from Aggregator class. It will provide you the unique ID for each object (each transaction) that you initialize. It will be the transaction id for the entire transaction.

Even though SagaTemplate<A> can be autowired anywhere in the application, As the best practice it is recommended to use SagaTemplate<A> inside of an EventHandler class according to the StackSaga design pattern called CHES.