This is a State Machine implementation based on the http://en.wikipedia.org/wiki/State_pattern From the classic book http://en.wikipedia.org/wiki/Design_Patterns Each state is a separate class. You can add methods to the state classes, but each state class must have implement the same list of methods. State transitions are the responsibility of the state classes.
Many other state machines focus on events and state transitions. This state machine focuses on behavior. The main benefit of this gem is to reduce conditional logic by removing #if checks in the model and moving the logic into the state objects. Using Composition in this way can go a long way to simplify Rails models.
Add this line to your application's Gemfile:
And then execute:
Or install it yourself as:
$ gem install state_objects
class WalkLights < ActiveRecord::Migration def self.change create_table :walk_lights do |t| t.string :color_state, :default => LightRedState.db_value end end class LightRedState < StateObjects::Base state_object_values :red, 'R', "Dont Walk" def change model.color_state_green! model.save! end end class LightGreenState < StateObjects::Base state_object_values :green, 'G', 'Walk' def change model.color_state_red! model.save! end end class WalkLight < ActiveRecord::Base extend StateObjects::ModelAdditions state_objects :color_state, LightGreenState, LightRedState state_object_events :color_state, :change scope :red, where(LightRedState.occurs ) scope :green, where(LightGreenState.occurs ) end # now lets use it north_south_elm_300_block = WalkLight.create(color_state: LightRedState.db_value) while (true) pause rand(200) # keep the pedestrians guessing :-) north_south_elm_300_block.change end
color_states returns a array of 2-value arrays suitable to fill a select tag The second example shows how to start the selection on a blank
<%= select :walk_light, :color_state, WalkLight.color_states %> <%= select :walk_light, :color_state, [['','']] + WalkLight.color_states %>
assert_equal "['Walk', 'Dont Walk']", WalkLight.color_state_js_list
adds the following INSTANCE METHODS to WalkLight
color_state # returns the single character value as in the db color_state_label # returns the current values label color_state_symbol # returns the current values symbol
- methods ending in '?' return boolean if the value is set
methods ending in '!' set the value ( this does NOT save the model)
walk_light = WalkLight.build(color_state: LightGreenState.db_value) walk_light.color_state_red! assert_equal 'R', walk_light.color_state assert_equal :red, walk_light.color_state_symbol assert_equal true, walk_light.color_state_red? assert_equal "Dont Walk", walk_light.color_state_label assert_equal [["Walk", "G"], ["Dont Walk", "R"]], WalkLight.color_states
<%= select :walk_light, :color_state, WalkLight.color_states %>
<% WalkLight.color_state_hash.each do | key, value | %> <%= radio_button :walk_light, :color_state, key %> <%= value %><br /> <% end %>
It's now easy to add scopes with using _occurs, which will generate your where statement for you.
scope :red, where(WalkLight.color_state_red_occurs ) # => "(color_state ='R')" scope :green, where(WalkLight.color_state_green_occurs ) # => "(color_state ='G')"
- Fork it
- Create your feature branch (
git checkout -b my-new-feature)
- Commit your changes (
git commit -am 'Add some feature')
- Push to the branch (
git push origin my-new-feature)
- Create new Pull Request
- Scott Baron - for helping with the unit tests.