Form Validation

Probably the most common use case is to validate form params. This is a special kind of a validation for a couple of reasons:

  • The input is a hash with stringified keys
  • The input can include values that are strings, hashes or arrays
  • Prior to validation, we need to coerce values and symbolize keys based on the information in the rules

For that reason, dry-validation ships with Params validation:

schema = Dry::Validation.Params do

  required(:age).filled(:int?, gt?: 18)

errors ='email' => '', 'age' => '18').messages

puts errors.inspect
# {
#   :email => ["must be filled"],
#   :age => ["must be greater than 18"]
# }

Form-specific value coercion is handled by a hash-schema using dry-types. It is built automatically for you based on the type expectations and used prior to applying the validation rules.

Handling Empty Strings

Your schema will automatically coerce empty strings to nil provided that you allow a value to be nil:

schema = Dry::Validation.Params do

  required(:age).maybe(:int?, gt?: 18)

result ='email' => '', 'age' => '')

puts result.output
# {:email=>'', :age=>nil}

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