Dozer and enums

While trying to map a persistent heavyweight class to a cleaner (and much smaller) POJO I also wanted to substitute some String parameters of the persistent class to Enums. The tool of choice is Dozer, of which I already wrote.

As I had the possibility to create the POJO from scratch I choose only the properties I needed and used the same names of the persistent class, thus having no need to write a custom mapping at all.

To check that everything was working fine I wrote a unit test - what else would you expect? :-) - as simple as that:

@Test
public void testPojoToPersistenceEntity() {
 System.out.println("testPojoToPersistenceEntity");
 MyPojo pojo = new MyPojo(
         propOne,
         propTwo,
         propThree,
         propFour);
 MyPersistentClass persistent = mapper.map(pojo, MyPersistentClass.class);
 assertNotNull(persistent);
 assertEquals(propOne, persistent.getPropOne());
 assertEquals(propTwoTxt, persistent.getPropTwo());
 assertEquals(propThreeTxt, persistent.getPropThree());
 assertEquals(propFour, persistent.getPropFour());
}

I run the test and got a green bar for free. You may notice that in the comparison there are a couple of different variables: these are the names of the Enums, and I was quite pleased with the fact that Dozer had silently mapped them just as I expected.

Happy as a clam I wrote another test for the other way round:

@Test
public void testPersistenceEntityToExistingPojo() {
  System.out.println("testPersistenceEntityToExistingPojo");
  MyPersistentClass persistent = new MyPersistentClass(
          propOne,
          propTwoTxt,
          propThreeTxt,
          propFour);
  persistent.setPropFive(propFive);
  persistent.setPropSix(propSix);
  MyPojo pojo = new MyPojo(
          propOne,
          propTwo,
          propThree,
          propFour);
  assertEquals(0d, pojo.getPropFive(), 0.01d);
  assertEquals(0d, pojo.getPropSix(), 0.01d);
  mapper.map(persistent, pojo);
  assertEquals(propFive, pojo.getPropFive(), 0.01d);
  assertEquals(propSix, pojo.getPropSix(), 0.01d);
}

Still smiling I hit the CTRL+F6 combination and... WTF? red bar?

org.dozer.MappingException: Illegal object type for the method 'setPropTwo'.
  Expected types:
      my.package.MyEnum
  Actual types:
      java.lang.String

Hmmm... weird... but not too much after all, I had been too optimistic.

After a little investigation, and taken for granted that I didn't want to write a custom mapper for each and every enumeration I could need, given the current conditions of use of the POJO I tried to map a one-way relationship. The problem is that when you mark a field as one-way Dozer only maps from <class-a> to <class-b>, while I needed exactly the opposite behaviour. Changing the order of the classes was not an option as we use the convention of mapping all the domain classes as <class-a> so I had to revert to the <field-exclude> syntax:

<mapping>
  <class-a>my.model.package.MyPersistentClass</class-a>
  <class-b>my.package.MyPojo</class-b>
      <field-exclude type="one-way">
          <a>propTwo</a>
          <b>propTwo</b>
      </field-exclude>
      <field-exclude type="one-way">
          <a>propThree</a>
          <b>propThree</b>
      </field-exclude>
</mapping>

Not exactly what I had in mind, because it doesn't let me create a new instance of a POJO, but for now it will suffice.

Any hints?