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Installation and Setup

Steps to add StructuredParams to a Rails application.

Table of Contents

Installation

Add the gem to your Gemfile:

gem 'structured_params'
bundle install

Or install it directly:

gem install structured_params

Setup

Register the custom types in a Rails initializer:

# config/initializers/structured_params.rb
StructuredParams.register_types

This registers the :object and :array types with ActiveModel::Type.

Configuration

You can configure StructuredParams in the same initializer:

# config/initializers/structured_params.rb
StructuredParams.register_types

StructuredParams.configure do |config|
  # Controls how array indices appear in human attribute names and full_messages.
  #   0 (default) — 0-based: "Hobbies 0 Name can't be blank"
  #   1           — 1-based: "Hobbies 1 Name can't be blank"
  config.array_index_base = 1
end
Option Default Description
array_index_base 0 Index base for array elements in error messages (0 or 1)

Note: array_index_base affects human_attribute_name and therefore full_messages. For APIs returning raw error keys (the typical pattern), this setting has no visible effect.

Custom Type Registration

To avoid naming conflicts with existing code, register the types under custom names:

StructuredParams.register_types_as(
  object_name: :structured_object,
  array_name:  :structured_array
)

# Then use in your parameter classes
class UserParams < StructuredParams::Params
  attribute :address, :structured_object, value_class: AddressParams
  attribute :hobbies, :structured_array,  value_class: HobbyParams
end