Improvements to Validation API!

This is issue is for suggesting improvements to the Javalin’s validation API (Validator/Rule classes)

To consider:

• Allow Nullable Types to Be Processed By Validator (https://github.com/tipsy/javalin/issues/991)
• Allow custom validation errors and validation rules overriding (https://github.com/tipsy/javalin/issues/993)
• Add validator method returning default value (https://github.com/tipsy/javalin/pull/835)

[MrThreepwood]

I’ll take a stab at adding something. I think the fundamental difference here is that you see args as some extra unrelated thing. I see the args as part of the error. The error returned from a check is not just a string, it is a string and a map/array of args. It doesn’t make any more sense to me to add the “args” for an error to the request attributes than it would to add the message. The message and the args go together. If the message is stored in the validator, the args should be stored in the validator.

I think I can add it in such a way that most users of the API won’t know the difference. I would still prefer that the predicate return the error rather than passing a predicate and a error separately, as it would allow for sane default errors from standardized validation checks, but I’ll just keep it to Adding the args for now.

[MrThreepwood]

The point is that you really can’t format the error after retrieving it from the validator. During validations, you have to tell the validator: check("start_date", { it > some_date && it < some_other_date }), “here’s an error”)`. This then fails, so you can now format it in the exception handler for validation errors, but what were the dates? How do you access them? You need to provide it to the front ends in the format I’ve described previously, so how do you do that?