How to use enums with JPA

Question

I have an existing database of a film rental system. Each film has a has a rating attribute. In SQL they used a constraint to limit the allowed values of this attribute.

Answer 1

Resolved!!! Where I found the answer: http://programming.itags.org/development-tools/65254/

Briefly, the convertion looks for the name of enum, not the value of attribute 'rating'. In your case: If you have in the db values "NC-17", you need to have in your enum:

enum Rating {
(...)
NC-17 ( "NC-17" );
(...)

Answer 2

The problem is, I think, that JPA was never incepted with the idea in mind that we could have a complex preexisting Schema already in place.

I think there are two main shortcomings resulting from this, specific to Enum:

1. The limitation of using name() and ordinal(). Why not just mark a getter with @Id, the way we do with @Entity?
2. Enum's have usually representation in the database to allow association with all sorts of metadata, including a proper name, a descriptive name, maybe something with localization etc. We need the easy of use of an Enum combined with the flexibility of an Entity.

Help my cause and vote on JPA_SPEC-47

Answer 3

use this annotation

@Column(columnDefinition="ENUM('User', 'Admin')")

Answer 4

What about this

public String getRating{  
   return rating.toString();
}

pubic void setRating(String rating){  
   //parse rating string to rating enum
   //JPA will use this getter to set the values when getting data from DB   
}  

@Transient  
public Rating getRatingValue(){  
   return rating;
}

@Transient  
public Rating setRatingValue(Rating rating){  
   this.rating = rating;
}

with this you use the ratings as String both on your DB and entity, but use the enum for everything else.

Answer 5

have you tried to store the ordinal value. Store the string value works fine if you don't have an associated String to the value:

@Enumerated(EnumType.ORDINAL)

Answer 6

Enum public enum ParentalControlLevelsEnum { U("U"), PG("PG"), _12("12"), _15("15"), _18("18");

private final String value;

ParentalControlLevelsEnum(final String value) {
    this.value = value;
}

public String getValue() {
    return value;
}

public static ParentalControlLevelsEnum fromString(final String value) {
    for (ParentalControlLevelsEnum level : ParentalControlLevelsEnum.values()) {
        if (level.getValue().equalsIgnoreCase(value)) {
            return level;
        }
    }
    return null;
}

}

compare -> Enum

public class RatingComparator implements Comparator {

public int compare(final ParentalControlLevelsEnum o1, final ParentalControlLevelsEnum o2) {
    if (o1.ordinal() < o2.ordinal()) {
        return -1;
    } else {
        return 1;
    }
}

}