Difference between revisions of "EclipseLink/Examples/JPA/EnumToCode"

Revision as of 10:44, 19 September 2009

How to map Enum to coded values

The JPA specification allows for mappings of Enums to database columns using the @Enumerated where the database value is either the Enum's name or ordinal value. EclipseLink allows a developer to map an enum to coded values as well using a converter.

In this example the enum Gender(MALE, FEMALE) is mapped to a single character in the database where M=MALE and F=FEMALE.

Gender Enum

The Gender enum in this example is defined as:

public enum Gender {
    Female, 
    Male
}

Defining the Converter

An ObjectTypeConverter is used and can be defined in an annotation and any entity class of persistence unit. It requires a unique name across all converters in this persistence unit.

@ObjectTypeConverter(name = "gender", objectType = Gender.class, dataType = String.class, conversionValues = {
		@ConversionValue(objectValue = "Male", dataValue = "M"),
		@ConversionValue(objectValue = "Female", dataValue = "F") })

Alternatively the converter can be defined in an EclipseLink specific ORM XML file as:

<object-type-converter name="gender" object-type="model.Gender"	data-type="java.lang.String">
	<conversion-value object-value="Male" data-value="M" />
	<conversion-value object-value="Female" data-value="F" />
</object-type-converter>

Using the Converter

The converter can then be used on any attribute in the domain model of the given enum type.

@Basic
@Convert("gender")
private Gender gender = Gender.Male;

Or in the ORM.XML:

<basic name="gender">
	<column name="GENDER" />
	<convert>gender</convert>
</basic>

Using ENUMs with JPA but without the evil ordinal()

A good article on insulating you JPA entities from changes to the enum values in database