Spring JPA repository: prevent update on save

Question

My user DB table looks like this:

CREATE TABLE user (
    username VARCHAR(32) PRIMARY KEY,
    first_name VARCHAR(256) NOT NULL,
    last_name          


        

Answer 1

One can perhaps use existsById(ID primaryKey) to test it, if userRepository extends CrudRepository:

if(userRepository.existsById(username)){
    //Throw your Exception
} else {
    this.userRepository.save(user);
}

see https://docs.spring.io/spring-data/jpa/docs/current/reference/html/