AssertJ: How to build custom and nested assertions - assertj

Question

I need to compare one PatientDTO dto object with other one PatientModel model object.
Both classes are quite similar:
class PatientDTO {
private String name;
private List<AddressDTO> address;
// Constructors, getters and setters
}
class PatientModel {
private String id;
private String nameElement;
private List<AddressModel> addressElement;
// Constructors, getters and setters
}
class AddressDTO {
private String city;
private String country;
private List<String> linesElement;
// Constructors, getters and setters
}
class AddressModel {
private String city;
private String countryElement;
private List<String> linesElement;
// Constructors, getters and setters
}
Main differences are:
Some fields are not present on DTOs: PatientDTO.id doesn't exist.
Some field names contains suffixes on Model classes: PatientDTO.name <> PatientModel.nameElement.
Other issue I like to solve, is that:
Address related assertion should be shared. I mean, Address-like classes are present on other classes, for exemple, Organization, Practitioner...
I'd like to build an assertion like this:
PatientDTO patientDTO;
PatientModel patientModel;
assertThat(patientDTO).isEqual(patientModel);
Shortly:
Should I build a custom assertion?
Should I have an assertion for Address an other one for Patient containing previous Address assertion? How could I get this?
What aboud Address assertion for Patient, Organization
What I want to avoid is code like this:
assertThat(patientDTO).anySatisfy(p->{
assertThat(p.getName()).withFailMessage("expected name: "+ p.getAddress().getCity()).isEqualTo(patientModel.getNameElement());
assertThat(p.getAddress().getCity()).withFailMessage("expected city: "+ p.getAddress().getCity()).isEqualTo(patientModel.getCityElement());
assertThat(p.getAddress().getCountry()).withFailMessage("expected country: "+ p.getAddress().getCountry()).isEqualTo(patientModel.getCountryElement());
...
}
);
I want to avoid above code since Patient classes are really large. Here I've shorted them for clarity purpouses.
Any ideas?

Answer 1

The field-by-field recursive comparison could help for this purpose:
PatientDTO patientDTO = new PatientDTO(...);
PatientModel patientModel = new PatientModel(...);
assertThat(patientDTO).usingRecursiveComparison()
.isEqualTo(patientModel);
Some fields are not present on DTOs: PatientDTO.id doesn't exist.
There are a few methods that can be used to tune the comparison and ignore fields:
Directly with ignoringFields(String…​ fieldsToIgnore)
By regexes with ignoringFieldsMatchingRegexes(String…​ regexes)
By types with ignoringFieldsOfTypes(Class…​ typesToIgnore)
Some field names contains suffixes on Model classes: PatientDTO.name <> PatientModel.nameElement.
This is currently not supported and was also asked in https://stackoverflow.com/a/70381488/9714611. We plan to raise a feature request about it and I will update the answer once the issue link is ready.
Address related assertion should be shared. I mean, Address-like classes are present on other classes, for exemple, Organization, Practitioner...
If the target is always isEqualTo, probably a custom assertion implementation is not needed as long as the limitation of the recursive comparison about not being able to compare fields with different names is not a show-stopper. These fields would require ad-hoc comparison until a better solution is available.
If the target is to provide assertions in a domain-specific language, like:
assertThat(patientDTO).hasAddress(addressDTO);
then a custom assertion implementation can be added.
Also, there is an assertions generator with plugins for Maven and Gradle that can be used to generate assertions based on the class attributes.