Clarification Needed on Using forEachIfPresent for Null/Empty Checks and Cross-Field Validation

[hrstoyanov]

I have these 2 interfaces:

interface User {
    @Nullable List<String> emails();
    @Nullable List<PassKey> passKeys();
}

interface PassKey {
   byte[] id();
   User user();
}

So, first I try to validate the emails a user can have like this:

    Validator<User> userValidator = ValidatorBuilder.<User>of()  
            .forEachIfPresent(User::emails,"emails", b->b._string(e->e,"email", CharSequenceConstraint::email))
            .build();

This compiles, but I am not sure (and there is no javadocs!) what "forEachIfPresent" means. Does it means that the validation will work if the emails list itself is not empty/null only, or does it mean it will skip NULL/empty email string elements? Because I need both - the validation should only happen if the list of emails is not null/empty, but there should be no NULLS or empty string emails inside. How do I do that?

Also I do not like the "e->e" stuff. I know I could use Function.identity(), anything better?

The second validation is more complicated - I want to make sure that passkeys in User (if there are any) always refer back the owning user, e.g. passkey.user() points back to the owning user. I looked at "cross-field validation" section in the docs, still no idea how to this - any clue?

[making]

Does it means that the validation will work if the emails list itself is not empty/null only, or does it mean it will skip NULL/empty email string elements?

IfPresent means if the fields is not null.

https://yavi.ik.am/#constraints-on-elements-in-a-collection-map-array

If the collection / map / array field is nullable, use forEachIfPresent instead of forEach.

If list is not null, validation will be run on each element, but if it is empty, nothing will happen a s a result.

https://yavi.ik.am/#built-in-constraints
Most built-in constraints, except notXXXX, do not validate fields if they are null. All examples include the case where the fields are null.

Also I do not like the "e->e" stuff. I know I could use Function.identity(), anything better?

Use Email object instead of String.

The second validation is more complicated - I want to make sure that passkeys in User (if there are any) always refer back the owning user, e.g. passkey.user() points back to the owning user. I looked at "cross-field validation" section in the docs, still no idea how to this - any clue?

Something like this?

Validator<User> userValidator = ValidatorBuilder.<User>of()
    .forEachIfPresent(User::emails, "emails", b -> b._string(e -> e, "email", c -> c.notEmpty().email()))
    .constraintOnTarget(new CustomConstraint<>() {
      @Override
      public String defaultMessageFormat() {
        return "tbd";
      }

      @Override
      public String messageKey() {
        return "tbd";
      }

      @Override
      public boolean test(User user) {
        List<PassKey> passKeys = user.passKeys();
        if (passKeys != null) {
          return passKeys.stream()
              .filter(passKey -> !Objects.equals(passKey.user(), user))
              .findAny()
              .isEmpty();
        }
        return true;
      }
    }, "passKeys")
    .build();

[hrstoyanov]

Thanks @making ,let me try that .. will post with any additional question. Closing this one now