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/

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.

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 String payload;

The Converter Class

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<String, String> {

    @Override
    public String convertToDatabaseColumn(String attribute) {
       return swapLetters(attribute);
    }

    @Override
    public String convertToEntityAttribute(String dbData) {
       return swapLetters(attribute);
    }

    private String swapLetters(String s) {
      ...
   }
}