How to map a Java class property that is an object to a single JPA table column?

Question

I have a Sprint Boot web service that is using JPA to map to an underlying SQL database.

One of the domain classes has a property that is a complex Java object that I do not want to persist with the normal mapped/joined tables. Instead I want to map this Java object to a single column in the main table, and ideally store the data in a JSON format in a string column.

Any suggestions?

Answer 1

You can use jpa's AttributeConverter :

@Converter
public class MyObjectConverter implements AttributeConverter<MyObject, String> {
 @Override
 public String convertToDatabaseColumn(MyObject myObject) {
    //convert myobject to json: for instance use ObjectMapper from Jackson
    if( myObject == null )
        return null;

    ObjectMapper mapper = new ObjectMapper();
    return mapper.writeValueAsString(myObject );
 }

 @Override
 public MyObject convertToEntityAttribute(String myObjectString) {
    // convert myObjectString back to object
    if( myObjectString== null )
        return null;

    ObjectMapper mapper = new ObjectMapper();
    return mapper.readValue(myObjectString, MyObject.class);
 }  
}

and use it in your entity as..

@Column
@Converter(converter = MyObjectConverter.class)
MyObject myObject;