Finite State Machine is a powerful Ruby gem that allows you to easily manage state transitions in your applications. Whether you are building a simple web application or a complex system, this gem provides a clean and intuitive way to define, manage, and trigger state transitions.
Installation
To install Finite State Machine, simply add the following line to your Gemfile:
gem 'finite_state_machine'
Then run the following command to install the gem:
bundle install
Usage
Finite State Machine provides a simple and intuitive way to define your states, events, and transitions. To get started, you need to define your state machine:
class Order
include FiniteStateMachine
state_machine initial: :new do
state :new, value: 0
state :processing, value: 1
state :shipped, value: 2
state :delivered, value: 3
event :process do
transition :new => :processing
transition :processing => :shipped
end
event :deliver do
transition :shipped => :delivered
end
end
end
In the example above, we define an order state machine with four states: new, processing, shipped, and delivered. We then define two events: process and deliver. The transitions define how the state machine moves from one state to another when an event is triggered.
To use the state machine in your application, create a new instance of the Order
class and call the specified events:
order = Order.new
order.process
order.deliver
The state of the Order
instance will automatically update when an event is triggered. You can access the current state using the current_state
method:
puts order.current_state # Output: delivered
Callbacks
Finite State Machine provides callbacks that allow you to execute code before or after specific state transitions. You can use these callbacks to perform additional actions or validations when a transition occurs.
To define a callback, simply add a block of code to the relevant transition. For example:
event :process do
transition :new => :processing, before: -> { do_something_before }
transition :processing => :shipped, after: -> { do_something_after }
end
In this example, the before
callback will execute the do_something_before
method before transitioning from the new state to the processing state. The after
callback will execute the do_something_after
method after transitioning from the processing state to the shipped state.
You can also define global callbacks that will be executed for all transitions, regardless of the specific event:
event :all, before: -> { do_something_before_all }
In this case, the do_something_before_all
method will be executed before any transition occurs.
Guards
Finite State Machine allows you to define guards, which are conditions that need to be met in order for a transition to occur. Guards can be used to perform conditional logic or validations before allowing a state transition.
To define a guard, simply add a block of code to the relevant transition. For example:
event :process do
transition :new => :processing, guard: -> { customer_valid? }
end
In this example, the transition from the new state to the processing state will only occur if the customer_valid?
method returns true
. If the method returns false
, the transition will not happen.
State Queries
Finite State Machine provides methods to query the state of an object. These methods can be useful when you need to perform different actions based on the current state of an object.
Here are some of the state query methods:
state_name?
: Returnstrue
if the object is in the specified state, otherwise returnsfalse
.state_name!
: Raises an exception if the object is not in the specified state.in_state?(:state_name)
: Returnstrue
if the object is in the specified state, otherwise returnsfalse
.current_state
: Returns the current state of the object.
Advanced Configuration
Finite State Machine provides advanced configuration options to handle more complex scenarios. These options include defining state value types, setting up multiple state machines for a single class, and specifying the initial state explicitly.
For detailed information on these advanced configuration options, including examples and use cases, please refer to the official documentation.
Conclusion
The Finite State Machine gem provides a clean and intuitive way to manage state transitions in your Ruby applications. Whether you are working on a small project or a large-scale system, this gem can help you organize and streamline your code. Try it out and discover the power of state machines!