I have the following projection in my Java (Spring Boot) app:

public interface DemoProjection {
    UUID getUuid();
    String getName();
    String getSurname();

    String getLabel();
    void setLabel(String label);

I want to set this label field in my service:

public DemoProjection findAByUuid(UUID uuid) {
        // returns a single record
        final DemoProjection demo =  demoRepository.findAByUuid(uuid);
        final String label = String.format(
                "Name: %s%nSurnamame Surname: %s",
                demo.geteName(),
                demo.getSurname());

        // ! this line throws error
        demo.setLabel(label);
        return demo;
    }

demo.setLabel(label); throws error: "cannot set projection A TupleBackedMap cannot be modified."

So, how can I set label field in the projection?

CodePudding user response：

You can't actually do that. Spring Data uses proxies and AOP to bind the query result to your projection interface, and since it's an interface you can't change that in a magical way. I would suggest creating a model/dto and map your projection values there:

public class DemoDto {
  private String uuid;
  private String name;
  private String surname;
  
  //getters and setters ommited for brevity
}

You can create a DemoDto object with your desired values.

In alternative, you can use a projection class instead of a projection interface. Check spring docs on how to do that :)

CodePudding user response：

Just create a default method in your DemoProjection interface to return getLabel formatted as you wish:

public interface DemoProjection {
  UUID getUuid();
  String getName();
  String getSurname();

  default String getLabel() {
      return String.format(
            "Name: %s%nSurnamame Surname: %s",
            geteName(),
            getSurname());
  }
}

this is required as you can't set a Projection after it has been created by JPA but since you only need formatting there is no need to set anything - default method does the trick.