If you don’t respect these two possibilities, then you will get bit in the butt alot, when you least expect it. To be fair, these situations can happen whether you’re using Hibernate or not, but when we first started using the framework we made lots of assumptions.

Here is a completely ridiculous example that violates the above restrictions:

public class User
{
  private boolean isSurnameLast;
  private Name name;  

  private String fullName;
  private String initials;

  public boolean setSurnameLast(boolean surnameLast)
  {
    this.isSurnameLast=surnameLast;
  }

  public void setName(Name name)
  {
    this.name = name;
    String lastName;
    String firstName;
    initials = new StringBuffer(name.getSurName().substring(0,1)).append(".").append(name.getGivenName().substring(0,1)).toString();
    if(isSurnameLast)
    {
      lastName = name.getSurName();
      firstName = name.getGivenName();
    }
    else
    {
      lastName = name.getGivenName();
      firstName = name.getSurName();
    }
    fullName = new StringBuffer(firstName).append(" ").append(lastName).toString();
  }
  // more getters and setters blah blah blah
}

(Ignore the lame “business logic” here…)

So you look in your database and you see that all the Users database entries have names and properly set surnameLast values, and all the Names database entries have a surName and a givenName. Sure the code is sloppy, but this is gonna work fine!

Nope, this setName is loaded with problems.

First, you’ll notice as your app runs that somehow setName is being called and passed a null. What?! Why! Durn that Hibernate, it is trying to trick you! No matter, we’ll catch it with a null check. You’ll shield your eyes as to when and why Hibernate or cglib or whatever is calling setters on an instance that isn’t even in the database, but at least it won’t blow up. This is the first bad smell you’ve blown through, you sloppy panicky codemonkey:

  public void setName(Name name)
  {
    if(name!=null) // hahah
   {
       this.name = name;
      ....

Then you’ll start realizing that no matter what the database says, sometimes you are getting the surname first in the full name! “Smith Joan!”, you’ll cry, but “it’s true for Joan Smith in the database! Why?” Well, sometimes Hibernate is calling setName before it calls setSurnameLast. It doesn’t matter which you have mapped first in the User.hbm.xml file, or which field you have first in the code. You can’t depend on other properties of User being initialized in the Hibernate setters.

Now, you’re also going to get NullPointerExceptions thrown out of this code, because sometimes that Name instance you’re being passed hasn’t had its properties initialized by Hibernate yet. Talk about something that seems sneaky and evil but is totally above board: Hibernate has created the new Name instance and has passed that reference to other instances, but hasn’t fully populated the Name instance yet.

That means this line will blow sky-high sometimes:

initials = new StringBuffer(name.getSurName().substring(0,1)).append(".").append(name.getGivenName().substring(0,1)).toString();

The sane thing to do here?

  public void setName(Name name)
  {
    this.name = name;
  }

So if you’re using Hibernate, go take a look at your classes and mappings! You may very well be doing something dangerous.

The Hibernate API allows you a lot of access to its configuration object model, and this is ideal for finding out how Hibernate is interacting with your code. I wrote a small class to do this inspection. The method below is run after a Hibernate Configuration object named creatively as “configuration” has been built with mapping files:

public Map findSetters() throws MappingException
{
  Map classToSetters = new HashMap();
  Iterator classMappingIterator =   configuration.getClassMappings();

  while(classMappingIterator.hasNext())
  {
    PersistentClass persistentClass = (PersistentClass)classMappingIterator.next();
    Class mappedClass = persistentClass.getMappedClass();
    Iterator propertyIt = persistentClass.getPropertyIterator();
    List classSetters = new LinkedList();

    classToSetters.put(mappedClass, classSetters);

    while(propertyIt.hasNext())
    {
      Property property = (Property)propertyIt.next();
      Setter setter = property.getSetter(mappedClass);

      classSetters.add(setter.getMethodName());
    }
  }
  return classToSetters;
}

I have uploaded a Java project that contains the full HibernateInspector class, as well as some sample classes and mappings. Un-tar it, and run

ant -Dhibernate.home="path to hibernate 3" 

to build and run the example.