Question

I have a model object that’s in fact an enum with fields and getters:

@Entity
public enum Type {
   TYPE1, TYPE2, TYPE3, TYPE4;

   @Column
   private Long id;
   @Column
   private String name;
   ...

   public String getName() {
      return this.name;
   }
   ...
}

It compiles and runs fine. However, if I call a getter method, it returns null (it doesn’t load any values stored in the database). Is this the standard behavior? Is there a way to make JPA load them?

Answer 1

I’d say there is some misconception in this aproach:

1. Entities represent objects that can be stored in the database. In this case, the database (or any other persistent store) defines which instances are available.

2. Enums represent a fixed set of constants that are defined in source code. Thus the class itself defines which constants are available. In addition, it’s generally bad practice to change the values of an enum, i.e. the name or id in your case.

You see that they are two quite different concepts which should be treated differently.

To store enums in entities (where the enum is a field of that entity), you could either use @Enumerated and store the name or ordinal of the enum, or (what we do more often) store one of the fields (we mostly use the id) and provide conversion methods.

If you want to store configurable “constants” in the database you might try and use plain entities for that, make the constructor private (Hibernate and other JPA providers should be able to deal with that) and provide an alternative implementation of the Enum class (you can’t use the enum keyword though).