Registering Converters in JPA 2.1 with EclipseLink

问题:

On JavaEE environment, I use JPA 2.1 implementation with EclipseLink,

I have some entities that contain enums. So I have created converters for these enumerations.

Car entity :

@Entity
public class Car implements Serializable {

    private static final long serialVersionUID = 6L;

    @Id
    private String      id;

    @Convert (converter = CarColorConverter.class)
    private CarColor    color;

    public enum CarColor {
        Black,
        Gray,
        White,
        Red
    };

    public Car () {
        id = GenerateUUID.id ();
    }

    ....
}

CarColor Converter :

@Converter (converterClass = CarColorConverter.class, name = "CarColorConverter") 
public class CarColorConverter implements AttributeConverter<CarColor, String> { 

    private static final String BLACK   = "Black";
    private static final String GRAY    = "Gray";
    private static final String WHITE   = "White";
    private static final String RED     = "Red";

    @Override
    public String convertToDatabaseColumn (CarColor entityData) {

        switch (entityData) {
            case Black:
                return BLACK;

            case Gray:
                return GRAY;

            case White:
                return WHITE;

            case Red:
                return RED;

            default:
                throw new IllegalArgumentException ("Unknown : " + entityData);
        }
    }

    @Override
    public CarColor convertToEntityAttribute (String dbData) {

        switch (dbData) {
            case BLACK:
                return CarColor.Black;

            case GRAY:
                return CarColor.Gray;

            case WHITE:
                return CarColor.White;

            case RED:
                return CarColor.Red;

            default:
                throw new IllegalArgumentException ("Unknown : " + dbData);
        }
    }
}

persistence.xml

<?xml version="1.0" encoding="UTF-8"?>
<persistence 
    version="2.1"
    xmlns="http://xmlns.jcp.org/xml/ns/persistence" 
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/persistence http://xmlns.jcp.org/xml/ns/persistence/persistence_2_1.xsd">

    <persistence-unit name="xyz-restful-api" transaction-type="RESOURCE_LOCAL">

        <!-- Converters -->
        <!--<class>com.xyz.model.converters.CarColorConverter</class>-->

        <!-- Entities / Model -->
        <class>com.xtz.model.Car</class>

        <properties>
            ...
        </properties>

    </persistence-unit>

</persistence>

1. When I comment the declaration of the converter on the persistence.xml file, and try to persist my entities in the DB I get this error : "Please ensure the converter class name is correct and exists with the persistence unit definition.". and no compilation time exception, only a warning pretty explicit :

   Class "com.xyz.model.converters.CarTypeConverter" is annotated, but not listed in the persistence.xml file

2. However, when I uncomment the declaration of the converter on the on the persistence.xml file, and try to persist my entities in the DB I get this error : "Please ensure the converter class name is correct and exists with the persistence unit definition.". and a compilation time exception :

   Class "com.xyz.model.converters.CarColorConverter" is listed in the persistence.xml file, but is not annotated

Am I declaring the converters in a wrong way ?

Thank you.

回答1:

Give this a try and ensure you have included the correct packages.

Car entity

Stays the same

import javax.persistence.Convert;

@Entity
public class Car implements Serializable {

    [...]

    @Convert(converter = CarColorConverter.class)
    private CarColor    color;

    [...]
}

CarColor Converter

You only need the empty Annotation

import javax.persistence.AttributeConverter;
import javax.persistence.Converter;

@Converter
public class CarColorConverter implements AttributeConverter<CarColor, String> {
    [...]
}

persistence.xml

You can either

• declare no class at all

or

• declare every class that is involved.

As soon as you need to declare an entity manually (e.g. when it resists in a library) then you also need do declare all other entity/converter classes.

<?xml version="1.0" encoding="UTF-8"?>
<persistence 
    version="2.1"
    xmlns="http://xmlns.jcp.org/xml/ns/persistence" 
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/persistence http://xmlns.jcp.org/xml/ns/persistence/persistence_2_1.xsd">

    <persistence-unit name="xyz-restful-api" transaction-type="RESOURCE_LOCAL">

        <!-- Converters -->
        <class>com.xyz.model.converters.CarColorConverter</class>

        <!-- Entities / Model -->
        <class>com.xtz.model.Car</class>

        [...]
    </persistence-unit>
</persistence>

回答2:

My guess is that you have intermixed javax.persistence and org.eclipse.persistence.annotations packages.

Using javax.persistence package classes, you may use an empty Converter annotation on the converter class and a Convert annotation on the entity class specifying the converter class.

回答3:

Just wanted to make the small remark, that the empty @Converter annotation is supported from JPA 2.1 up via EclipseLink 1. You find the used JPA version under project(rightclick)->properties->facets.

Also note that as mentioned above, if you start to add a single class in the persistence.xml you have to add everything.

回答4:

Wait till they release the patch for your application server.

https://bugs.eclipse.org/bugs/show_bug.cgi?id=443546

The release schedules pending are listed in http://www-01.ibm.com/support/docview.wss?uid=swg27004980

The workaround for now is to store it as a String and have a getter and setter that would do the transform for you like this

public final class StaticEnumToStringConverter {

    public static <E extends Enum<E>> String convertToDatabaseColumn(final E attribute) {

        if (attribute == null) {
            return null;
        }
        return attribute.toString();
    }

    public static <E extends Enum<E>> E convertToEntityAttribute(final String dbData, final Class<E> enumClass) {

        if (dbData == null) {
            return null;
        }
        for (final E c : EnumSet.allOf(enumClass)) {
            if (dbData.equals(c.toString())) {
                return c;
            }
        }
        throw new IllegalArgumentException(dbData);

    }

    private StaticEnumToStringConverter() {

    }
}

Then use in the JPA Entity as:

@NotNull
@Column(nullable = false)
private String genderAtBirth;

public Gender getGenderAtBirth() {
    return StaticEnumToStringConverter.convertToEntityAttribute(genderAtBirth, Gender.class);
}
public void setGenderAtBirth(final Gender genderAtBirth) {

    this.genderAtBirth = StaticEnumToStringConverter.convertToDatabaseColumn(genderAtBirth);
}