dry-validation

Error Messages

By default dry-validation comes with a set of pre-defined error messages for every built-in predicate. They are defined in a yaml file which is shipped with the gem. This file is compatible with I18n format.

You can provide your own messages and configure your schemas to use it like that:

schema = Dry::Validation.Schema do
  configure { config.messages_file = '/path/to/my/errors.yml' }
end

You can also provide a namespace per-schema that will be used by default:

schema = Dry::Validation.Schema do
  configure { config.namespace = :user }
end

Lookup rules:

en:
  errors:
    size?:
      arg:
        default: "size must be %{num}"
        range: "size must be within %{left} - %{right}"

      value:
        string:
          arg:
            default: "length must be %{num}"
            range: "length must be within %{left} - %{right}"

    filled?: "must be filled"

    included_in?: "must be one of %{list}"
    excluded_from?: "must not be one of: %{list}"

    rules:
      email:
        filled?: "the email is missing"

      user:
        filled?: "name cannot be blank"

        rules:
          address:
            filled?: "You gotta tell us where you live"

Given the yaml file above, messages lookup works as follows:

messages = Dry::Validation::Messages::YAML.load(%w(/path/to/our/errors.yml))

# matching arg type for size? predicate
messages[:size?, rule: :name, arg_type: Fixnum] # => "size must be %{num}"
messages[:size?, rule: :name, arg_type: Range] # => "size must be within %{left} - %{right}"

# matching val type for size? predicate
messages[:size?, rule: :name, val_type: String] # => "length must be %{num}"

# matching predicate
messages[:filled?, rule: :age] # => "must be filled"
messages[:filled?, rule: :address] # => "must be filled"

# matching predicate for a specific rule
messages[:filled?, rule: :email] # => "the email is missing"

# with namespaced messages
user_messages = messages.namespaced(:user)

user_messages[:filled?, rule: :age] # "cannot be blank"
user_messages[:filled?, rule: :address] # "You gotta tell us where you live"

By configuring messages_file and/or namespace in a schema, default messages are going to be automatically merged with your overrides and/or namespaced.

I18n Integration

If you are using i18n gem and load it before dry-validation then you’ll be able to configure a schema to use i18n messages:

require 'i18n'
require 'dry-validation'

schema = Dry::Validation.Schema do
  configure { config.messages = :i18n }

  required(:email).filled
end

# return default translations
schema.call(email: '').messages
{ :email => ["must be filled"] }

# return other translations (assuming you have it :))
puts schema.call(email: '').messages(locale: :pl)
{ :email => ["musi być wypełniony"] }

Important: I18n must be initialized before using a schema, dry-validation does not try to do it for you, it only sets its default error translations automatically.

Full Messages

By default, messages do not include a rule’s name, if you want it to be included simply use :full option:

schema.call(email: '').messages(full: true)
{ :email => ["email must be filled"] }

Finding the right key

dry-validation has one error key for each kind of validation (Refer to errors.yml for the full list). key? and filled? can usually be mistaken for eachother, so pay attention to them:

  • key?: a required parameter is missing in the params hash.
  • filled?: a required parameter is in the params hash but has an empty value.