Aggregator Serialization

Creating SagaSerializable Class for Aggregator

Providing sample objects for the framework is very important to capture the feature failures that can be occurred due to the version updates of the Aggregator. You can have a better understanding of version updates through the following topics.

Aggregator’s Event Casting

Let’s look at the implementation of SagaSerializable here:

The SagaSerializable class provides you a method called <T> getSamples() to provide the sample array of objects of your real Aggregator. for each aggregator class that you made should have a separate implementation of SagaSerializable for validating the sample object before the application is started. that process ensures that your aggregator object will not face a serialization error while the transactions are being processed in the production.

you can see a sample SagaSerializable (PlaceOrderAggregatorSample.class) implementation of the PlaceOrderAggregator.

public class PlaceOrderAggregatorSample extends SagaSerializable<PlaceOrderAggregator> { (1)
    public PlaceOrderAggregatorSample() {
        //sample-1
        PlaceOrderAggregator aggregator1 = new PlaceOrderAggregator();
        aggregator1.setOrderId(UUID.randomUUID().toString());

        this.put("1", aggregator1);(2)

        //sample-2
        PlaceOrderAggregator aggregator2 = new PlaceOrderAggregator();
        aggregator2.setOrderId(UUID.randomUUID().toString());
        aggregator2.setUsername("mafei");

        this.put("2", aggregator2);(2)

        //sample-3
        PlaceOrderAggregator aggregator3 = new PlaceOrderAggregator();
        aggregator3.getItemDetails().add(
                PlaceOrderAggregator.ItemDetail
                        .builder()
                        .itemName("Item-01")
                        .price(10.50)
                        .qty(2)
                        .build()
        );

        this.put("3", aggregator3); (2)
    }
}

1	Implement your custom `PlaceOrderAggregatorSample` from the `SagaSerializable<T>`. The generic type should be the aggregator that you wish to check the sample object. According to the example, the Type is `PlaceOrderAggregator`. Then you will have a method for providing the sample objects for that given type.
2	Put your initialized sample objects for the validation process by using `put(key,vlaue)` method. The key should be unique for each. And also you have to provide at least one sample object.

Make sure to keep the default constructor for each SagaSerializable implementation.

Aggregator Serialization And Deserialization

By default, StackSaga uses Jackson ObjectMapper for aggregator serialization and deserialization. Therefore, It is possible to do default casting subject to ObjectMapper in StackSaga. To do that you are able to use all the jackson-annotations that are provided by the Jackson ObjectMapper Library.

It is recommended to use @JsonProperty annotation with a fixed-name for all the properties in your aggregator class. It helps to keep the JSON properties safe from the Java codes in the event-store.
The suggestion does not mean to keep the properties in SNAKE_CASE at all. Therefore, it is not recommended to use SNAKE_CASE configuration for all the properties in your aggregator class. Because it will be changed correspondingly to the property name every time you change the property name in the Java code.

@SagaAggregator(
        version = @SagaAggregatorVersion(major = 1, minor = 0, patch = 1),
        idPrefix = "po",
        name = "PlaceOrderAggregator",
        sagaSerializable = PlaceOrderAggregatorSample.class,
        mapper = PlaceOrderAggregatorJsonMapper.class
)
@Getter
@Setter
public class PlaceOrderAggregator extends Aggregator {

    public PlaceOrderAggregator() {
        super(PlaceOrderAggregator.class);
    }

    @JsonProperty("order_id")
    private String orderId;
    @JsonProperty("username")
    private String username;
    @JsonProperty("total")
    private Double total;
    @JsonProperty("is_active")
    private int isActive;
    @JsonProperty("item_details")
    private List<ItemDetail> itemDetails = new ArrayList<>();
    ...
}