converting between transfer and domain objects

Joachim Van der Auwera

What is a tranfer object

Class with only getters and setters

Project Lombok recommended

@DataPublic class PersonTo { private String firstName; private String lastName; private String gender; private String birthday;}

Why use transfer objects

Decouple API and domain model

Manage application boundaries (e.g. transactions)

@Data@EntityPublic class Person { @Id Private Long id; @Basic private String firstName; @Basic private String lastName; @Basic private Gender gender; @Basic private LocalDate birthday;}

How?

Stupid boilerplate conversion code

Public Person toDomain( PersonTo to) { Person res = new Person();

Res.setFirstName( to.getFirstName()); ... Return res;}

Not always simple...

Null checks

Domain lookup

Type conversion

Still boilerplate !

Gender gender;if (StringUtils. isBlank(to.getGender)) { Gender = null;} else { Gender = Gender.valueOf( to.getGender());}res.setGender(gender);

In the real world...

Project for Flemish Government, REST API

almost 10% of the code was custom conversion between TO and domain objects

Inconsistent conversion behaviour

Stupid work, easy to make mistakes

Testing

Automate

Automatic conversion...

jTransfo

dozer

jTransfo features

Easy to use

Annotation based

No dependencies

Many transfer objects one domain object

Security enabled

Integrations

Spring framework

CDI

Joda-time

Hibernate

JRebel

Works well with Project Lombok (highly recommended!)

Easy conversion

JTransfo jTransfo = new JTransfoImpl();SomeDomain domainObject = jTransfo. convertTo(transferObject, SomeDomain.class);

SomeDomain domainObject = new SomeDomain();jTransfo.convert(transferObject, domainObject);

List list = jTransfo. convertList(transferObjects, SomeDomain.class);

Easy conversion

@Data@DomainClass("pkg.Person")public class PersonTo { private String name;

@MappedBy(field = country, path = addr) private String addrCountry;

@MappedBy(readOnly = true) private String gender;

@NotMapped private String globaalNummer;}

@MapOnlies({ @MapOnly("create"), @MapOnly(value = "*", readOnly = true)})private String somefield;

Security

jTransfo.convertTo(transferObject, SomeDomainClass.class, create, admin);

Type conversion and lists

@MappedBy(typeConverter = "filterToList")private List filters;

@MappedBy(typeConverter = "readOnlyDomain")private LayerTo layer;

Type conversion, Spring config

ORM link, object finder

Automatically build new / linked object

Find in Hibernate maybe

Always consistent

Use ReadOnlyDomain to either update links only or linked object contents as well

Inheritance support

Declare child types to convert to correct object

Normal annotations on child classes (correct domain class)

@DomainClass(value = "pkg.ObjectDomain")@DomainClassDelegate(delegates = { SomeChildTo.class, OtherChildTo.class})public class ObjectTo {

Convert interceptor

Set method to call on each convert invocation

Validations

Side effects

T convert( Object source, T target, boolean isTargetTo, ConvertSourceTarget next, String... tags);

www.jtransfo.org

https://github.com/joachimvda/jtransfo

@joachimvda

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