Map enum in JPA with fixed values ?

Posted by Kartoch on Stack Overflow See other posts from Stack Overflow or by Kartoch
Published on 2010-05-01T22:14:59Z Indexed on 2010/05/01 23:37 UTC
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I'm looking for the different ways to map an enum using JPA. I especially want to set the integer value of each enum entry and to save only the integer value.

@Entity
@Table(name = "AUTHORITY_")
public class Authority implements Serializable {

  public enum Right {
      READ(100), WRITE(200), EDITOR (300);

      private int value;

      Right(int value) { this.value = value; }

      public int getValue() { return value; }
  };

  @Id
  @GeneratedValue(strategy = GenerationType.AUTO)
  @Column(name = "AUTHORITY_ID")
  private Long id;

  // the enum to map : 
  private Right right;
}

A simple solution is to use the Enumerated annotation with EnumType.ORDINAL:

@Column(name = "RIGHT")
@Enumerated(EnumType.ORDINAL)
private Right right;

But in this case JPA maps the enum index (0,1,2) and not the value I want (100,200,300).

Th two solutions I found do not seem simple...

First Solution

A solution, proposed here, uses @PrePersist and @PostLoad to convert the enum to an other field and mark the enum field as transient:

@Basic
private int intValueForAnEnum;

@PrePersist
void populateDBFields() {
  intValueForAnEnum = right.getValue();
}

@PostLoad
void populateTransientFields() {
  right = Right.valueOf(intValueForAnEnum);
}

Second Solution

The second solution proposed here proposed a generic conversion object, but still seems heavy and hibernate-oriented (@Type doesn't seem to exist in JEE):

@Type(
    type = "org.appfuse.tutorial.commons.hibernate.GenericEnumUserType",
    parameters = {
            @Parameter(
                name  = "enumClass",                      
                value = "Authority$Right"),
            @Parameter(
                name  = "identifierMethod",
                value = "toInt"),
            @Parameter(
                name  = "valueOfMethod",
                value = "fromInt")
            }
)

Is there any other solutions ?

I've several ideas in mind but I don't know if they exist in JPA:

  • use the setter and getter methods of right member of Authority Class when loading and saving the Authority object
  • an equivalent idea would be to tell JPA what are the methods of Right enum to convert enum to int and int to enum
  • Because I'm using Spring, is there any way to tell JPA to use a specific converter (RightEditor) ?

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