Best practices for handling unique constraints with Hibernate

[spice ruin]

Stack: java 17, spring boot, hibernate 6, postgres

Suppose we have a user entity with two unique fields - username and email.
When I try to create a new user with session.persist(userEntity), it throws a org.hibernate.exception.ConstraintViolationException, which is of course correct.
The exception contains all information for the programmer to see what's wrong, but, I'm trying to display a user-friendly error to the user (web UI), not an exception message.
The only thing that comes to my mind is to check each field explicitly, something like:

boolean emailExists = session.createQuery("select 1 from User where email = :email")
    .setParameter("email", user.getEmail())
    .uniqueResultOptional()
    .isPresent();

if (emailExists) {
   // handle email already exists
}

boolean usernameExists = session.createQuery("select 1 from User where username = :username")
    .setParameter("username", user.getUsername())
    .uniqueResultOptional()
    .isPresent();

if (usernameExists){
   // handle username already exists
}

session.persist(user);

The code above works, but it doesn't look like the ideal solution because:

• we talk to the database (up to) 3 times instead of only once
• duplication of business logic, we've already created unique database indexes and annotated our entities with @Column(unique=true), adding another explicit check for uniqueness seems kinda... wrong

Thanks in advance ✌️

[weak nimbus]

Detected code, here are some useful tools:

Formatted code

boolean emailExists = session.createQuery("select 1 from User where email = :email").setParameter("email", user.getEmail()).uniqueResultOptional().isPresent();
if (emailExists) {
  // handle email already exists
}
boolean usernameExists = session.createQuery("select 1 from User where username = :username").setParameter("username", user.getUsername()).uniqueResultOptional().isPresent();
if (usernameExists) {
  // handle username already exists
}
session.persist(user);

<@&987246584574140416> please have a look, thanks.