Add error message value formatter to the numericality validator

[joaomangilli]

Summary

Sometimes, we need to format the value being shown in an error message in the numericality validator (like greater_than_or_equal_to: 25, we want to format the number 25 to something like 25.00) to match a monetary value or something like that.

This PR opens an option to format that value the way you need it.

[rafaelfranca]

Makes sense. Can you add a CHANGELOG entry?

[joaomangilli]

@rafaelfranca done

[jonathanhefner]

@joaomangilli Do you have a use-case in mind that would benefit from :value_format instead of specifying a :message Proc? A :message Proc can access the validation value via :count, e.g.:

validates_numericality_of :approved, greater_than: 50000, 
  message: -> (record, data) { "must be greater than #{do_something(data[:count])}" }

Perhaps this could be improved by allowing the :message Proc to modify and return the data Hash, thus still relying on the framework to perform interpolation? e.g.:

validates_numericality_of :approved, greater_than: 50000, 
  message: -> (record, data) { data.merge(count: do_something(data[:count])) }

[joaomangilli]

@jonathanhefner thanks! I think this is a best way to solve the problem. This can pave the way for solving more problems. I'll make the change.

[jonathanhefner]

@joaomangilli To clarify: I'm not sure if returning a Hash from a :message Proc is the best way to solve this. I was just brainstorming out loud. 😃

Another possibility might be using Errors#generate_message or a similar method. For example, if the data Hash included the non-humanized attribute name and the error type, you could write something like:

validates_numericality_of :approved, greater_than: 50000, message: -> (record, data) do 
  data[:count] = do_something(data[:count])
  record.errors.generate_message(data[:attribute_symbol], data[:type], data)
end

[joaomangilli]

@jonathanhefner sorry, I wanted to say that it looks like a better (not the best) solution.

But the more I think about it the more I think that this validator should offer a native option to format the count value, without the need to deal with the message.

I know that this value is part of the message, but I think it makes sense to pass this value already formatted, so we don't have to deal with it in the message.

Because to do this in the message, we need to change the method of the message to offer more options or flexibility and it still won't solve the problem, as we will still need to use this method to "interpolate" the formatted value in the message.

What do you think?

[joaomangilli]

@rafaelfranca can we go ahead with this?

[rails-bot]

This pull request has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs.
Thank you for your contributions.

[rails-bot]

This pull request has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs.
Thank you for your contributions.