HV000028: Unexpected exception during isValid call - spring

Question

I created a custom validation rule to check if a username exists in the database.
My User class has a username that has a custom validation rule that when an object is created it checks in the database if that same username exists.
I use an interface UserRepository extends JpaRepository<User, Integer> to save the users to the database and in the custom validation rule to check if the username already exists. I make use of
#Autowired
UserRepository userRepository;
Separately I can validate users and save them to the database, but when using them together like calling userRepository.save(user); the #Autowired UserRepository userRepository; in the custom validation rule does not get initiated so it remains null.
javax.validation.ValidationException: HV000028: Unexpected exception during isValid call.
Custom validation rule
public class UsernameConstraintValidator implements ConstraintValidator<Username, String> {
#Autowired
UserRepository userRepository;
#Override
public boolean isValid(String s, ConstraintValidatorContext constraintValidatorContext) {
return !userRepository.existsUserByUsername(s);
}
}
Trying to save user in the controller
#PostMapping("/save")
public String save(#Valid #ModelAttribute("user") User user,BindingResult result, #RequestParam String password2){
if(result.hasErrors()) return "register";
userRepository.save(user);
return "login";
}
Here is the full stack trace: https://justpaste.it/7rnx7
Here is the full project: https://github.com/leotrimvojvoda/todo

Answer 1

Add spring.jpa.properties.javax.persistence.validation.mode=none in application.propperties
I found the answer in this thread: Spring-Boot How to properly inject javax.validation.Validator
This answer includes the solution to the problem that I was having with bean validation and hibernate.
"...because Hibernate doesn't know about the Spring Context and as far as I can tell there is no way to tell it, not even with the LocalValidatorFactoryBean. This causes the Validator's to run twice. One correctly, and once that fails."
In short the solution is to tell hibernate to not run the validation by adding the following line in your application.propperties
spring.jpa.properties.javax.persistence.validation.mode=none
I suggest you read the full answer of this question to better understand it's implications with LocalValidatorFactoryBean.
Credits also go to João Dias for helping me find this answer.

Answer 2

Your Custom Validation class does not seem a Spring managed bean. Try adding #Component annotation to it as follows:
#Component
public class UsernameConstraintValidator implements ConstraintValidator<Username, String> {
#Autowired
UserRepository userRepository;
#Override
public boolean isValid(String s, ConstraintValidatorContext constraintValidatorContext) {
return !userRepository.existsUserByUsername(s);
}
}
Update 06/09/2021
As it seems (according to https://stackoverflow.com/a/13361762/16572295) you also need to setup a LocalValidatorFactoryBean to have this working:
#Bean
public Validator validatorFactory() {
return new LocalValidatorFactoryBean();
}