well_formed-dry_types

dry-types coercion integration for WellFormed form objects.

Declare typed attributes with dry_attribute and coercion runs automatically before validation — keeping your forms free of manual casting logic.

Installation

bundle add well_formed-dry_types

Usage

Require the gem in your application:

require "well_formed-dry_types"

Include WellFormed::DryTypes in any form, then use dry_attribute in place of attribute for fields that need type coercion:

module Types
  include Dry.Types()
end

class CreateOrderForm < WellFormed::ResourceForm
  include WellFormed::DryTypes

  resource_alias :order

  dry_attribute :quantity, Types::Params::Integer
  dry_attribute :amount,   Types::Params::Decimal
  dry_attribute :status,   Types::String.enum("pending", "confirmed")

  validates :quantity, presence: true, numericality: {greater_than: 0}
  validates :amount,   presence: true
  validates :status,   presence: true
end

Coercion runs before validation. If coercion fails, an error is added to the attribute and validation is skipped for that field:

form = CreateOrderForm.new(order, current_user, {quantity: "abc", amount: "9.99", status: "pending"})
form.valid?
# => false
form.errors[:quantity]
# => ["must be Params::Integer"]  # dry-types error message

Custom error messages

Pass message: to override the default dry-types error message.

I18n key

dry_attribute :status, Types::String.enum("pending", "confirmed"), message: :inclusion

Passes the symbol to errors.add, which resolves it through your I18n translations.

Literal string

dry_attribute :amount, Types::Params::Decimal, message: "must be a number"

Default (no message option)

dry_attribute :quantity, Types::Params::Integer

Falls back to the error message from dry-types itself.

Inheritance

_dry_attributes merges up the superclass chain, so subclass forms inherit parent coercions and can add their own:

class BaseOrderForm < WellFormed::ResourceForm
  include WellFormed::DryTypes
  dry_attribute :amount, Types::Params::Decimal
end

class CreateOrderForm < BaseOrderForm
  dry_attribute :quantity, Types::Params::Integer
  # inherits :amount coercion from BaseOrderForm
end

API

Class macro	Description
dry_attribute(name, type, message: nil)	Declares a coerced attribute. Coercion runs before validation via a before_validate callback.

How it works

When WellFormed::DryTypes is included, a before_validate callback (_coerce_dry_attributes) is registered. Before each validation run, every dry_attribute is coerced in declaration order. On Dry::Types::CoercionError, an error is added and the raw value is left in place. Subsequent validators can still run against the failing attribute (e.g. a presence check on a nil optional).

License

MIT