JPA Attribute Converter

External

• https://www.thoughts-on-java.org/jpa-21-how-to-implement-type-converter
• https://www.thoughts-on-java.org/jpa-21-type-converter-better-way-to/
• https://www.thoughts-on-java.org/how-to-use-jpa-type-converter-to/

Internal

• JPA Concepts

Overview

An attribute converter allows the developer to specify methods to convert between the database and the Java representation of an attribute. Attribute conversion was introduced in JPA 2.1. All entity class. mapped superclass or embeddable class attributes can be type-converted, with the following exceptions:

• identity (@Id) attributes
• version (@Version) attributes
• relationship attributes (@OneToOne, @OneToMany, @ManyToOne, @ManyToMany)
• attributes annotated as @Temporal or @Enumerated.

Playground Example

https://github.com/ovidiuf/playground/tree/master/spring/jpa/attribute-converter

Programming Model

@Convert Annotation

Annotate the entity fields to be converter with @javax.persistence.Convert:

@Convert(converter = PayloadConverter.class)
private Payload payload;

The Converter Class

https://docs.oracle.com/javaee/7/api/javax/persistence/AttributeConverter.html

Provide a converter class, which must implement AttributeConverter<Entity-Field-Type, Database-Type> and be annotated with @javax.persistence.Converter:

@Converter
public class PayloadConverter implements AttributeConverter<Payload, String> {

  @Override
  public String convertToDatabaseColumn(Payload attribute) {
     ...
  }

  @Override
  public Payload convertToEntityAttribute(String dbData) {
     ...
  }
}