DDD, Anti Corruption layer, how-to?
In my particular implementation, EmployeeAccessService is called by a Repository. It's really a facade into the Anti-corruption layer. It delegates to the EmployeeAccessAdapter. The adapter fetches an object from the legacy model (which it gets from EmployeeAccessFacade),then passes it to the EmployeeAccessTranslator to transform the object from the legacy model to the domain object in my application's model.
EmployeeAccessService
public Employee findEmployee(String empID){
return adapter.findEmployee(empID);
}
EmployeeAccessAdapter
public Employee findEmployee(String empID){
EmployeeAccessContainer container = facade.findEmployeeAccess(empID);
return translator.translate(container);
}
EmployeeAccessTranslator
public Employee translate(EmployeeAccessContainer container){
Employee emp = null;
if (container != null) {
employee = new Employee();
employee.setEmpID(idPrefix + container.getEmployeeDTO().getEmpID());
...(more complex mappings)
From the DDD book (Domain-Driven Design: Tackling Complexity in the Heart of Software) by Eric Evans:
The public interface of the ANTICORRUPTION LAYER usually appears as a set of SERVICES, although occasionally it can take the form of an ENTITY.
and a bit later
One way of organizing the design of the ANTICORRUPTION LAYER is as a combination of FACADES, ADAPTERS (both from Gamma et al. 1995), and translators, along with the communication and transport mechanisms usually needed to talk between systems.
So, you might find examples by looking at the suggested adapter pattern and facade pattern.
I'll try to paraphrase what Eric Evans said, your anti-corruption layer will appear as services to the outside of your layer. So outside of the anti-corruption layer the other layers will not know they are "speaking" with a anti-corruption layer. Inside of the layer you would use adapters and facades to wrap your legacy information sources.
More information about the anti-corruption layer:
- Anatomy of an Anti-Corruption Layer, Part 1
- Building the often needed anti-corruption layer