Using enums with entity beans

[dsouza]

Hi,

I've been playing around with java 5 type-safe enums and persistence works neatly with them. But I have a question.

Take for example this very simple enum:

public enum MyEnum implements Serializable {
 HIGH,
 LOW
}

If I create an entity bean that has MyEnum as one of it's fields, it will persist HIGH as 0 and LOW as 1 in the database since they are the respective ordinals for each item in the enum.

Now let's say I need to change this enum to:

public enum MyEnum implements Serializable {
 HIGH,
 MEDIUM,
 LOW
}

This breaks my implementation since now LOW = 2. Of course I could just place the MEDIUM after LOW, but this is just an example of what I would need to do. In order to maintain the order inside my code (specially on larger enums) It would be great if I could just add to my enum anywhere I wanted to.

So I thought I could do something such as:

public enum MyEnum implements Serializable {
 HIGH(1000),
 LOW(100)

...
}

By doing this I would have to have a constructor for the enum and a method to retrieve the value I'm passing. Now I could easily add a MEDIUM(500) right in the middle.
But the persistence layer would still be calling ordinal() to obtain an ordinal value to persist in the database. I can't override the ordinal() method because it's final. Is there any way I can get the container to call a different method to obtain an ordinal value for each enum? Any other ideas on how this could be solved?

[epbernard]

you can create an Hibernate UserType and use @Type

[dsouza]

Exactly what I was looking for! Thanks!

However it is the first time I use @Type and I'm having some problems.

As in the docs, I created a UserType class, implemented all methods:

public class EnumUserType implements UserType {

public Class returnedClass() {
 return ConditionType.class;
}

public int[] sqlTypes() {
 return new int[] { Types.NUMERIC };
}
...

and made the appropriate changes in my entity bean:

@Type(type = "mypackage.EnumUserType")
@Column(name = "COND_TYPE", nullable = false)
public ConditionType getConditionType() {
...

ConditionType is an enum as I described in my previous post.

now I'm getting this when I deploy:

org.hibernate.MappingException: Could not determine type for: mypackage.EnumUserType, for columns: [org.hibernate.mapping.Column(COND_TYPE)]
 at org.hibernate.mapping.SimpleValue.getType(SimpleValue.java:266)
 at org.hibernate.mapping.SimpleValue.isValid(SimpleValue.java:253)
...

Still can't figure out what I'm doing wrong. Any ideas on what might be causing this?

[dsouza]

Never mind that last post... It was a typo in my package's name.

[onormann]

You also can use the @Enumerated - annotation and choose the type ORDINAL or STRING, so you won't get problems with the order of newly added enum-constants.

@Enumerated(EnumType.STRING)
@Column(name="CATEGORY", nullable=false)
private Category category;