Fix: mutually_exclusive and exactly_one_of validation error messages now label parameters as strings, consistently with requires and optional.

[dblock]

I was getting

"[:user_id, :profile_id]" => ["- exactly one parameter must be provided"]

but at the same time

"user_id" => ["is missing"]

This also enables returning JSON, ie. not translating an array of parameters into a string.

[dblock]

@oliverbarnes and @Morred, check this out pls.

[dblock]

You get a mutually exclusive error when more than one are present, so this is only used when none are present.

[oliverbarnes]

makes sense 👍

[dblock]

For reference, I've also added a JSON formatter to the validation errors. The README now says:

The default response from a Grape::Exceptions::ValidationErrors is a humanly readable string, such as "beer, wine are mutually exclusive", in the following example.

params do
  optional :beer
  optional :wine
  optional :juice
  exactly_one_of :beer, :wine, :juice
end

You can rescue a Grape::Exceptions::ValidationErrors and respond with a custom response or turn the response into well-formatted JSON for a JSON API that separates individual parameters and the corresponding error messages. The following rescue_from example produces [{"params":["beer","wine"],"messages":["are mutually exclusive"]}].

format :json
subject.rescue_from Grape::Exceptions::ValidationErrors do |e|
  rack_response e.to_json, 400
end

[dblock]

Note that you cannot just turn ValidationErrors#errors into a hash, JSON doesn't allow multiple values in the key.

[oliverbarnes]

I like that, nice + elegant solution