Actions have four parts to them (responsibliities, I suppose):
- execution
- supporting methods for perform the validation etc
- target object that they act upon
- event publishing
Our programming model could provide several syntaxes to put these responsibilities in different places. It already supports two (standard actions, and mixins).
To compare these syntaxes, we'll use a concrete example:
public class Customer { // target
...
public static class PlaceOderEvent extends ActionDomainEvent<Customer> {}
@Action(domainEvent = PlaceOrderEvent.class) // event publishing
public Customer placeOrder(Product p, int quantity) { ... } // execution
public boolean hidePlaceOrder() { return this.isBlackListed(); } // supporting methods
public String disablePlaceOrder() { return clockService.outsideShoppingHours(); }
public String disable1PlaceOrder(Product p) { return p.isOutOfStock() ? "Out of stock": null; }
public Collection<Product> choices0PlaceOrder() { ... }
public Product default0PlaceOrder() { return orderService.findLastProductPurchasedBy(this); }
public int default1PlaceOrder() { return 1; }
public String validate1PlaceOrder(int quantity) { return quantity <= 0 ? "Can only order +ve amounts": null; }
public String validatePlaceOrder(Product p, int quantity) { return catalogService.runningLowOn(p) && quantity > 4 ? "We're running low on that product, no more than 4" : null; }
...
@Inject CatalogService catalogService;
@Inject ClockService clockService;
@Inject OrderService orderService;
}
Notes:
- For disable1PlaceOrder(), we could also hide individual parameters similarly
- Instead of choices0PlaceOrder(), we could have used autoComplete0PlaceOrder(String)
Standard syntax
The standard syntax uses regular methods on the target object. Naming conventions are used to associate the action with supporting methods (default, choices, hide, disable and validate).
Here's the same example as before, but with implementation stripped out so that it is easier to compare with the alternate syntaxes that follow:
public class Customer {
public Customer placeOrder(Product p, int quantity) { ... }
public boolean hidePlaceOrder() { ... }
public String disablePlaceOrder() { ... }
public String disable1PlaceOrder(Product p) { ... }
public Collection<Product> choices0PlaceOrder() { ... }
public Product default0PlaceOrder() { ... }
public int default1PlaceOrder() { ... }
public String validate1PlaceOrder(int quantity) { ... }
public String validatePlaceOrder(Product p, int quantity) { ... }
}
Mixins syntax
Mixins change the target, by allowing this set of methods to be moved to a different object target:
public class Customer { ... }
@Action // or @Mixin(method="act") and a bunch of other annotations
public class Customer_placeOrder() { // infer action name from the mixin class name
private final Customer target; // constructor omitted
public Customer act(Product p, int quantity) { ... }
public boolean hideAct() { ... }
public String disableAct() { ... }
public String disable1Act(Product p) { ... }
public Collection<Product> choices0Act() { ... }
public Product default0Act() { ... }
public int default1Act() { ...}
public String validate1Act(int quantity) { ... }
public String validateAct(Product p, int quantity) { ... }
}
Instead of \@Action, the \@Mixin(method="act") could also be used, with additional annotations on the "act" method. I've chosen the version with the least boilerplate here.
Parameters syntax (proposed)
Per this thread on slack, we could introduce a Parameters object (in Java 14+, this might be a record) to bring together all of the parameters into a single object. This would make it easier to avoid issues with numbering etc.
This syntax
public class Customer {
@Value @Accessors(fluent = true)
public class PlaceOrderParameters {
Product product;
int quantity;
}
public Customer placeOrder(Product p, int quantity) { ... }
public boolean hidePlaceOrder() { ... }
public String disablePlaceOrder() { ... }
public String disable1PlaceOrder(PlaceOrderParameters params) { ... }
public Collection<Product> choices0PlaceOrder() { ... }
public Product default0PlaceOrder() { ... }
public int default1PlaceOrder() { ... }
public String validate1PlaceOrder(PlaceOrderParameters params) { ... }
public String validatePlaceOrder(PlaceOrderParameters params) { ... }
}
The \@Value \@Accessors(fluent=true) allows us to use a syntax that is very similar to Java 14 records.
Note that there is some duplication here: the list of the parameter types appears both in the "placeOrder(...)" method, as well as in the PlacerOrdersParameters class.
The above would also be supported with mixins:
@Action
public class Customer_placeOrder {
@Value @Accessors(fluent = true)
public static class PlaceOrderParameters {
Product product;
int quantity;
}
public Customer act(Product p, int quantity) { ... }
public boolean hideAct() { ... }
public String disableAct() { ... }
public String disable1Act(PlaceOrderParameters params) { ... }
public Collection<Product> choices0Act() { ... }
public Product default0Act() { ... }
public int default1Act() { ... }
public String validate1Act(PlaceOrderParameters params) { ... }
public String validateAct(PlaceOrderParameters params) { ... }
}
Parameters on Act syntax (proposed)
This is a variant of the previous, but uses the parameters class in the action as well: