Hibernate Mapping: Class having more than one possible value from an enum

Question

I am doing a simple web page and I have a NurseForm entity. When the nurse sees a patient he/she fills this form.

One of this form field is "Actions done" which is basically an enum with:

public enum NurseAction {
    GIVE_MEDICINE, PERFORM_SUTURE, SPRAY_THERAPY, NEBULIZATIONS;
}

A nurse can perform more than one action so I have a property:

private Collection<NurseAction> nurseActions;

From what I understand I need NurseAction to be an Entity, but if I do so I should populate the db by hand.

Can I avoid that? Which is the best way to solve this?

PS: I am a complete newbie to Hibernate.

Answer 1

You can try using @CollectionOfElements(targetElement=NurseAction.class) (you can try to omit the attribute and let hibernate assume it based on the type parameter of the collection)

Note that this annotation is deprecated in hibernate 3.5, in favour of the same annotation from JPA 2.0.

Answer 2

Unfortunately, Hibernate does not (yet) support collections of Enums properly. But do you not think that new actions will most likely be added later on? I would recommend going for an Entity for the action to make sure that you do not have to re-deploy your whole app just because you are adding an action...

Of course, you can also always do something (ugly :) like this:

@Entity public class NurseForm {
   private String actions;

   public void setActions(final List<NurseAction> actions) {
     if(actions == null)
        this.actions = null;
     else
        this.actions = Joiner.on(',').join(actions);
   }

   public List<NurseAction> getActions() {
      List<NurseAction> returner = Lists.newArrayList();
      if(this.actions != null) {
         Iterable<String> actions = Splitter.on(',').split(this.actions);
         for(String action : actions)
            returner.add(NurseAction.valueOf(action);
      }
      return returner;
   }
}

Disclaimer: all of this is untested and even un-compiled. Also, I am making heavy use of google guava because I love it. :)

Good luck!

Answer 3

Under the assumption that any action may only be applied once to a patient, i would suggest using Set instead of Collection. Please correct me if this does not fit your requirements. In case set semantic is ok, i would suggest using an EnumSet to store the actions. It's extremely fast and a compliant Set implementation. It uses a single long value under the hood (as long as you have less than 64 actions).

Now my solution would be to store a single number column to the database using custom UserType which maps from EnumSet to long and vice versa.

Pros

• single column
• fast
• extremely small overhead

Cons

• values in database are hard to read (by humans)
• custom queries are difficult

If you want to take a look at a generic abstract reusable implementation of such a UserType, take a look at http://source.palava2.org/browse/commons.svn.cosmocode.de/cosmocode-hibernate/trunk/src/main/java/de/cosmocode/hibernate/EnumSetUserType.java?r=HEAD