Adds support for integrating state machines with Sequel models.
Below is an example of a simple state machine defined within a Sequel model:
class Vehicle < Sequel::Model state_machine :initial => :parked do event :ignite do transition :parked => :idling end end end
The examples in the sections below will use the above class as a reference.
By default, the action that will be invoked when a state is transitioned is the save action. This will cause the resource to save the changes made to the state machine's attribute. Note that if any other changes were made to the resource prior to transition, then those changes will be made as well.
For example,
vehicle = Vehicle.create # => #<Vehicle @values={:state=>"parked", :name=>nil, :id=>1}> vehicle.name = 'Ford Explorer' vehicle.ignite # => true vehicle.refresh # => #<Vehicle @values={:state=>"idling", :name=>"Ford Explorer", :id=>1}>
As described in StateMachine::InstanceMethods#state_machine, event attributes are created for every machine that allow transitions to be performed automatically when the object's action (in this case, :save) is called.
In Sequel, these automated events are run in the following order:
before validation - Run before callbacks and persist new states, then validate
before save - If validation was skipped, run before callbacks and persist new states, then save
after save - Run after callbacks
For example,
vehicle = Vehicle.create # => #<Vehicle @values={:state=>"parked", :name=>nil, :id=>1}> vehicle.state_event # => nil vehicle.state_event = 'invalid' vehicle.valid? # => false vehicle.errors.full_messages # => ["state_event is invalid"] vehicle.state_event = 'ignite' vehicle.valid? # => true vehicle.save # => #<Vehicle @values={:state=>"idling", :name=>nil, :id=>1}> vehicle.state # => "idling" vehicle.state_event # => nil
Note that this can also be done on a mass-assignment basis:
vehicle = Vehicle.create(:state_event => 'ignite') # => #<Vehicle @values={:state=>"idling", :name=>nil, :id=>1}> vehicle.state # => "idling"
This technique is always used for transitioning states when the save action (which is the default) is configured for the machine.
Beware that public event attributes mean that events can be fired whenever mass-assignment is being used. If you want to prevent malicious users from tampering with events through URLs / forms, the attribute should be protected like so:
class Vehicle < Sequel::Model set_restricted_columns :state_event # set_allowed_columns ... # Alternative technique state_machine do ... end end
If you want to only have some events be able to fire via mass-assignment, you can build two state machines (one public and one protected) like so:
class Vehicle < Sequel::Model set_restricted_columns :state_event # Prevent access to events in the first machine state_machine do # Define private events here end # Allow both machines to share the same state state_machine :public_state, :attribute => :state do # Define public events here end end
In order to ensure that any changes made during transition callbacks are rolled back during a failed attempt, every transition is wrapped within a transaction.
For example,
class Message < Sequel::Model end Vehicle.state_machine do before_transition do |transition| Message.create(:content => transition.inspect) false end end vehicle = Vehicle.create # => #<Vehicle @values={:state=>"parked", :name=>nil, :id=>1}> vehicle.ignite # => false Message.count # => 0
Note that only before callbacks that halt the callback chain and failed attempts to save the record will result in the transaction being rolled back. If an after callback halts the chain, the previous result still applies and the transaction is not rolled back.
To turn off transactions:
class Vehicle < Sequel::Model state_machine :initial => :parked, :use_transactions => false do ... end end
If using the save action for the machine, this option will be ignored as the transaction will be created by Sequel within save.
If an event fails to successfully fire because there are no matching transitions for the current record, a validation error is added to the record's state attribute to help in determining why it failed and for reporting via the UI.
For example,
vehicle = Vehicle.create(:state => 'idling') # => #<Vehicle @values={:state=>"parked", :name=>nil, :id=>1}> vehicle.ignite # => false vehicle.errors.full_messages # => ["state cannot transition via \"ignite\""]
If an event fails to fire because of a validation error on the record and not because a matching transition was not available, no error messages will be added to the state attribute.
To assist in filtering models with specific states, a series of class methods are defined on the model for finding records with or without a particular set of states.
These named scopes are the functional equivalent of the following definitions:
class Vehicle < Sequel::Model class << self def with_states(*states) filter(:state => states) end alias_method :with_state, :with_states def without_states(*states) filter(~{:state => states}) end alias_method :without_state, :without_states end end
Note, however, that the states are converted to their stored values before being passed into the query.
Because of the way scopes work in Sequel, they can be chained like so:
Vehicle.with_state(:parked).order(:id.desc)
All before/after transition callbacks defined for Sequel resources behave in the same way that other Sequel hooks behave. Rather than passing in the record as an argument to the callback, the callback is instead bound to the object and evaluated within its context.
For example,
class Vehicle < Sequel::Model state_machine :initial => :parked do before_transition any => :idling do put_on_seatbelt end before_transition do |transition| # log message end event :ignite do transition :parked => :idling end end def put_on_seatbelt ... end end
Note, also, that the transition can be accessed by simply defining additional arguments in the callback block.
# File lib/state_machine/integrations/sequel/versions.rb, line 5 def self.active? !defined?(::Sequel::MAJOR) || ::Sequel::MAJOR == 2 || ::Sequel::MAJOR == 3 && ::Sequel::MINOR <= 13 end
Whether this integration is available. Only true if Sequel::Model is defined.
# File lib/state_machine/integrations/sequel.rb, line 229 def self.available? defined?(::Sequel::Model) end
Should this integration be used for state machines in the given class? Classes that include Sequel::Model will automatically use the Sequel integration.
# File lib/state_machine/integrations/sequel.rb, line 236 def self.matches?(klass) klass <= ::Sequel::Model end
# File lib/state_machine/integrations/sequel/versions.rb, line 26 def action_hook action == :save ? :save : super end
# File lib/state_machine/integrations/sequel/versions.rb, line 13 def handle_save_failure 'save_failure(:save)' end
# File lib/state_machine/integrations/sequel/versions.rb, line 9 def handle_validation_failure 'raise_on_save_failure ? save_failure(:validation) : result' end
Adds a validation error to the given object
# File lib/state_machine/integrations/sequel.rb, line 254 def invalidate(object, attribute, message, values = []) object.errors.add(self.attribute(attribute), generate_message(message, values)) end
# File lib/state_machine/integrations/sequel/versions.rb, line 23 def load_inflector end
Pluralizes the name using the built-in inflector
# File lib/state_machine/integrations/sequel.rb, line 264 def pluralize(word) load_inflector super end
Resets any errors previously added when invalidating the given object
# File lib/state_machine/integrations/sequel.rb, line 259 def reset(object) object.errors.clear end
Forces the change in state to be recognized regardless of whether the state value actually changed
# File lib/state_machine/integrations/sequel.rb, line 242 def write(object, attribute, value, *args) result = super column = self.attribute.to_sym if (attribute == :state || attribute == :event && value) && owner_class.columns.include?(column) && !object.changed_columns.include?(column) object.changed_columns << column end result end
Creates a new callback in the callback chain, always ensuring that it's configured to bind to the object as this is the convention for Sequel callbacks
# File lib/state_machine/integrations/sequel.rb, line 395 def add_callback(type, options, &block) options[:bind_to_object] = true options[:terminator] = @terminator ||= lambda {|result| result == false} super end
Creates a scope for finding records with a particular state or states for the attribute
# File lib/state_machine/integrations/sequel.rb, line 376 def create_with_scope(name) lambda {|model, values| model.filter(:"#{owner_class.table_name}__#{attribute}" => values)} end
Creates a scope for finding records without a particular state or states for the attribute
# File lib/state_machine/integrations/sequel.rb, line 382 def create_without_scope(name) lambda {|model, values| model.filter(~{:"#{owner_class.table_name}__#{attribute}" => values})} end
Adds hooks into validation for automatically firing events. This is a bit more complicated than other integrations since Sequel doesn't provide an easy way to hook around validation calls
# File lib/state_machine/integrations/sequel.rb, line 311 def define_action_helpers super if action == :save define_helper :instance, def valid?(*args) yielded = false result = self.class.state_machines.transitions(self, :save, :after => false).perform do yielded = true super end if yielded || result result else #{handle_validation_failure} end end, __FILE__, __LINE__ + 1 end end
Uses custom hooks for :save actions in order to preserve failure behavior within Sequel. This is a bit more complicated than other integrations since Sequel doesn't provide an easy way to hook around save calls.
# File lib/state_machine/integrations/sequel.rb, line 337 def define_action_hook if action == :save define_helper :instance, def #{action_hook}(*) yielded = false result = self.class.state_machines.transitions(self, :save).perform do yielded = true super end if yielded || result result else #{handle_save_failure} end end, __FILE__, __LINE__ + 1 else super end end
Skips defining reader/writer methods since this is done automatically
# File lib/state_machine/integrations/sequel.rb, line 300 def define_state_accessor name = self.name owner_class.validates_each(attribute) do |record, attr, value| machine = record.class.state_machine(name) machine.invalidate(record, :state, :invalid) unless machine.states.match(record) end end
Defines an initialization hook into the owner class for setting the initial state of the machine before any attributes are set on the object
# File lib/state_machine/integrations/sequel.rb, line 278 def define_state_initializer # Hooks in to attribute initialization to set the states *prior* to # the attributes being set define_helper :instance, # Initializes dynamic states def initialize(*) super do |*args| self.class.state_machines.initialize_states(self, :static => false) changed_columns.clear yield(*args) if block_given? end end # Initializes static states def set(*) self.class.state_machines.initialize_states(self, :dynamic => false) if values.empty? super end, __FILE__, __LINE__ + 1 end
Runs a new database transaction, rolling back any changes if the yielded block fails (i.e. returns false).
# File lib/state_machine/integrations/sequel.rb, line 388 def transaction(object) object.db.transaction {raise ::Sequel::Error::Rollback unless yield} end
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