The Rails framework provides a large number of helpers for working with assets, dates, forms, numbers and Active Record objects, to name a few. These helpers are available to all templates by default.
In addition to using the standard template helpers provided in the Rails framework, creating custom helpers to extract complicated logic or reusable functionality is strongly encouraged. By default, the controller will include a helper whose name matches that of the controller, e.g., MyController will automatically include MyHelper.
Additional helpers can be specified using the helper class method in ActionController::Base or any controller which inherits from it.
Examples
The to_s method from the Time class can be wrapped in a helper method to display a custom message if the Time object is blank:
module FormattedTimeHelper
def format_time(time, format=:long, blank_message=" ")
time.blank? ? blank_message : time.to_s(format)
end
end
FormattedTimeHelper can now be included in a controller, using the helper class method:
class EventsController < ActionController::Base
helper FormattedTimeHelper
def index
@events = Event.find(:all)
end
end
Then, in any view rendered by EventController, the format_time method can be called:
<% @events.each do |event| -%>
<p>
<% format_time(event.time, :short, "N/A") %> | <%= event.name %>
</p>
<% end -%>
Finally, assuming we have two event instances, one which has a time and one which does not, the output might look like this:
23 Aug 11:30 | Carolina Railhawks Soccer Match N/A | Carolina Railhaws Training Workshop
The helper class method can take a series of helper module names, a block, or both.
- *args: One or more modules, strings or symbols, or the special symbol :all.
- &block: A block defining helper methods.
Examples
When the argument is a string or symbol, the method will provide the "_helper" suffix, require the file and include the module in the template class. The second form illustrates how to include custom helpers when working with namespaced controllers, or other cases where the file containing the helper definition is not in one of Rails’ standard load paths:
helper :foo # => requires 'foo_helper' and includes FooHelper helper 'resources/foo' # => requires 'resources/foo_helper' and includes Resources::FooHelper
When the argument is a module it will be included directly in the template class.
helper FooHelper # => includes FooHelper
When the argument is the symbol :all, the controller will include all helpers beneath ActionController::Base.helpers_dir (defaults to app/helpers/**/*.rb under RAILS_ROOT).
helper :all
Additionally, the helper class method can receive and evaluate a block, making the methods defined available to the template.
# One line
helper { def hello() "Hello, world!" end }
# Multi-line
helper do
def foo(bar)
"#{bar} is the very best"
end
end
Finally, all the above styles can be mixed together, and the helper method can be invoked with a mix of symbols, strings, modules and blocks.
helper(:three, BlindHelper) { def mice() 'mice' end }
[ show source ]
# File actionpack/lib/action_controller/helpers.rb, line 114
114: def helper(*args, &block)
115: args.flatten.each do |arg|
116: case arg
117: when Module
118: add_template_helper(arg)
119: when :all
120: helper(all_application_helpers)
121: when String, Symbol
122: file_name = arg.to_s.underscore + '_helper'
123: class_name = file_name.camelize
124:
125: begin
126: require_dependency(file_name)
127: rescue LoadError => load_error
128: requiree = / -- (.*?)(\.rb)?$/.match(load_error.message).to_a[1]
129: if requiree == file_name
130: msg = "Missing helper file helpers/#{file_name}.rb"
131: raise LoadError.new(msg).copy_blame!(load_error)
132: else
133: raise
134: end
135: end
136:
137: add_template_helper(class_name.constantize)
138: else
139: raise ArgumentError, "helper expects String, Symbol, or Module argument (was: #{args.inspect})"
140: end
141: end
142:
143: # Evaluate block in template class if given.
144: master_helper_module.module_eval(&block) if block_given?
145: end
Declares helper accessors for controller attributes. For example, the following adds new name and name= instance methods to a controller and makes them available to the view:
helper_attr :name attr_accessor :name
[ show source ]
# File actionpack/lib/action_controller/helpers.rb, line 179
179: def helper_attr(*attrs)
180: attrs.flatten.each { |attr| helper_method(attr, "#{attr}=") }
181: end
Declare a controller method as a helper. For example, the following makes the current_user controller method available to the view:
class ApplicationController < ActionController::Base
helper_method :current_user, :logged_in?
def current_user
@current_user ||= User.find_by_id(session[:user])
end
def logged_in?
current_user != nil
end
end
In a view:
<% if logged_in? -%>Welcome, <%= current_user.name %><% end -%>
[ show source ]
# File actionpack/lib/action_controller/helpers.rb, line 163
163: def helper_method(*methods)
164: methods.flatten.each do |method|
165: master_helper_module.module_eval "def \#{method}(*args, &block) # def current_user(*args, &block)\ncontroller.send(%(\#{method}), *args, &block) # controller.send(%(current_user), *args, &block)\nend # end\n"
166: end
167: end
Provides a proxy to access helpers methods from outside the view.
[ show source ]
# File actionpack/lib/action_controller/helpers.rb, line 184
184: def helpers
185: unless @helper_proxy
186: @helper_proxy = ActionView::Base.new
187: @helper_proxy.extend master_helper_module
188: else
189: @helper_proxy
190: end
191: end