Ruby on Rails- constraints in ruby on rails - ruby on rails tutorial - rails guides - rails tutorial - ruby rails

We can filter what routes are available using constraints.

There are several ways to use constraints including:

segment constraints
request based constraints
advanced constraints

example

requested based constraint to only allow a specific IP address to access a route:

constraints(ip: /127\.0\.0\.1$/) do
  get 'route', to: "controller#action"
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See other similar examples ActionDispatch::Routing::Mapper::Scoping.

We want to do something more complex we can use more advanced constraints and create a class to wrap the logic:

# lib/api_version_constraint.rb
class ApiVersionConstraint
  def initialize(version:, default:)
    @version = version
    @default = default
  end

  def version_header
    "application/vnd.my-app.v#{@version}"
  end

  def matches?(request)
    @default || request.headers["Accept"].include?(version_header)
  end
end

# config/routes.rb
require "api_version_constraint"

Rails.application.routes.draw do
  namespace :v1, constraints: ApiVersionConstraint.new(version: 1, default: true) do
    resources :users # Will route to app/controllers/v1/users_controller.rb
  end

  namespace :v2, constraints: ApiVersionConstraint.new(version: 2) do
    resources :users # Will route to app/controllers/v2/users_controller.rb
  end
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One form, several submit buttons

We can also use the value of the submit tags of a form as a constraint to route to a different action. If we have a form with multiple submit buttons (eg "preview" and "submit"), We could capture this constraint directly in our routes.rb, instead of writing javascript to change the form destination URL.
Example with the commit_param_routing gem we can take advantage of rails submit_tag
Rails submit_tag first parameter lets we change the value of our form commit parameter

# app/views/orders/mass_order.html.erb
<%= form_for(@orders, url: mass_create_order_path do |f| %>
    <!-- Big form here -->
  <%= submit_tag "Preview" %>
  <%= submit_tag "Submit" %>
  # => <input name="commit" type="submit" value="Preview" />
  # => <input name="commit" type="submit" value="Submit" />
  ...
<% end %>

# config/routes.rb
resources :orders do
  # Both routes below describe the same POST URL, but route to different actions 
  post 'mass_order', on: :collection, as: 'mass_order',
    constraints: CommitParamRouting.new('Submit'), action: 'mass_create' # when the user presses "submit"
  post 'mass_order', on: :collection,
    constraints: CommitParamRouting.new('Preview'), action: 'mass_create_preview' # when the user presses "preview"
  # Note the `as:` is defined only once, since the path helper is mass_create_order_path for the form url
  # CommitParamRouting is just a class like ApiVersionContraint
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