Unable to load Aggregate using Repository.load() for Integer AggregateIdentifier - repository

Question

I've been trying in vain to load an aggregate using the load method of the repository class. I know that the load() method requires a string argument but my aggregate identifier is integer.
I have tried to convert to string, yet I'm not able to load the aggregate. I keep getting null.
My code is shown below
#Autowired
private Repository<Product> repository;
#CommandHandler
public Order(CreateOrderCommand cmd){
try{
//This line throws an error
Product product = (Product) repository.load(Integer.toString(cmd.getProductId()));
}
catch (Exception ex){
System.out.println("Oops! Error Occured: " + ex.getMessage());
}
apply(
new OrderCreatedEvent(
cmd.getOrderId(), cmd.getPrice(), cmd.getNumber(), cmd.getProductId()
)
);
}
I'm providing an more updates:
I simply want to update the products stock, when a new order is placed. So what I did was that in the CommandHandler for creating a new Order, I simply find the Product aggregate and call it's UpdateStock method, which is a command handler.
Is there something I really don't understand?
These are the files below:
The Product aggregate:
#Aggregate
public class Product {
#AggregateIdentifier
private String id;
private Double price;
private Integer stock;
private String description;
public Product() {
}
#CommandHandler
public Product(AddProductCommand cmd){
apply( new ProductAddedEvent(
cmd.getId(),
cmd.getPrice(),
cmd.getStock(),
cmd.getDescription()
)
);
}
#CommandHandler
public void updateStock (UpdateStockCommand cmd){
if(this.stock >= cmd.getStock()){
apply(new StockUpdatedEvent(cmd.getId(), cmd.getStock()));
}
else {
throw new RuntimeException("Out of Stock!");
}
}
#EventSourcingHandler
public void on(StockUpdatedEvent evt){
id = evt.getId();
stock = stock - evt.getStock();
}
#EventSourcingHandler
public void on(ProductAddedEvent evt){
id = evt.getId();
price = evt.getPrice();
stock = evt.getStock();
description = evt.getDescription();
}
}
The Order aggregate:
#Aggregate
public class Order {
#AggregateIdentifier
private String orderId;
private Double price;
private Integer number;
private String productId;
//Repository provides an abstraction for storage of Aggregates
#Autowired
private Repository<Product> repository;
#CommandHandler
public Order(CreateOrderCommand cmd){
try{
//This line throws an error
Product product = (Product) repository.load(cmd.getProductId());
}
catch (Exception ex){
System.out.println("Oops! Error Occured: " + ex.getMessage());
}
apply(
new OrderCreatedEvent(
cmd.getOrderId(), cmd.getPrice(), cmd.getNumber(), cmd.getProductId()
)
);
}
#EventSourcingHandler
public void on(OrderCreatedEvent evt){
orderId = evt.getOrderId();
price = evt.getPrice();
number = evt.getNumber();
productId = evt.getProductId();
}
}

Answer 1

As you have noticed, Axon will enforce a String for the aggregate identifier. This doesn't mean you need to provide a String directly. It'll work perfectly fine as long as you have a sensible toString() method implemented. Hence, using Integer as the aggregate identifier will result in the toString() result of that field to be used as the aggregate identifier.
Having said that, I'm surprised you are unable to load an aggregate based on this.
Maybe we need to do some follow up based on that, but firstly I want to comment on the snippet you're sharing.
It seems like you have a constructor command handler on the Order class. Moreover, that signals to me that the Order class is an aggregate.
I'd like to state that by no means would I ever recommend to load in an Aggregate from within another Aggregate.
Doing so ties in the lock on the Order aggregate with the Product aggregate, thus blocking a larger portion of your system than the sender of CreateOrderCommand would ever expect.
Communication between aggregate should be kept asynchronous at all times, through means of event messages.
That thus requires a dedicated Event Handling Component which does the coordination between both instances based on the published event.
I'd thus strongly suggest a rewrite of your logic on the matter.
When it comes to loading in an aggregate, I'd be hard pressed to give you a reasoning right now.
Hence, let me ask a couple of follow up questions.
I'd suggest to update your original request with the responses by the way; to maintain a nice thread of continuity.
Which version of Axon are you using any way?
Are you using any interesting configurations around the Product aggregate?
Are you pairing your application with Axon Server? If so, standard or enterprise, and which version?
Do you use the Configuration API directly or the axon-spring-boot-starter?
Update
Thanks for updating your question Kindson, let me update my answer too.
Firstly, as I already stated previously, I would never load in an Aggregate from within another Aggregate. Both your Order class and Product class are Aggregates and the snippets make overly clear that you are consolidating the "product Repository" from within the Order aggregate.
This approach does not only prolong locks on your aggregates, thus imposing strains on your users, but following this approach might event incur deadlocks. As a rule of thumb, always follow an asynchronous approach to communicating between aggregate instances. Thus a component reacting on an aggregate's events and dispatching commands to another. This can be done in a regular Event Handling Component, or a Saga for example.
Apart from the above, I have tested locally whether I could use an Integer as an Aggregate Identifier. Thus, as the #AggregateIdentifier annotated field in the aggregate and as the #TargetAggregateIdentifier annotated field on your command message. On top of that, I tried this out by having the framework call the Repository#load(String) operation (thus just dispatching a command on the CommandGateway/CommandBus) and by calling it directly as you did.
Sadly, this works out fine for me. Thus, as another follow up, I'd suggest to share the actual exception you are getting when you are performing the Repository#load(String) operation.