vavr Validation stream of validators

Question

I have a code like this:

  return validators
            .stream()
            .flatMap(v -> v.validate(scoreRequest).stream())
            .collect(toList());

Each validator returns a List<String> of errors, if the list is empty it means that the request is valid.

Now I want to introduce vavr.Validator. The new return type of each validator.validate now is Validation<List<String>,ScoreRequest>

How can I combine the output of each validators using streams like before?

I think you have to clarify your requirements. How could we tell you what *you* intend to do with that changed signature?! You changed the signature of that method to return a validation object. Now *you* have to determine how you want to reasonably process that?! — GhostCat, Apr 16 '19 at 07:06
I just want to combine all the validations performed by each validator. The output of the combine should be: `Validation,ScoreRequest>` — Fabry, Apr 16 '19 at 07:10
You say that **each** validate() method returns a Validation object. How do you expect to merge those? How do you get from a list of ScoreRequest to a single one?! — GhostCat, Apr 16 '19 at 07:31
I thought that the Valivation.combine would have done exactly this. Combine the `List` of errors or return the scoreRequest if the request is valid — Fabry, Apr 16 '19 at 08:04

score 1 · Accepted Answer · answered Apr 19 '19 at 18:17

You can use sequence to do exactly that.

So if your validators is a List<Validation<List<String>, ScoreRequest>>, applying this function to it will return a Validation<Seq<String>, Seq<ScoreRequest>>, which looks exactly like what you want. I let you figure out the plumbing of converting back the Seqs to whatever structure you want.

vavr Validation stream of validators

1 Answers1