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rails--rails/activesupport/lib/active_support/callbacks.rb
Bogdan Gusiev a21b5771ad AS::Callbacks: Refactor :per_key option
2012-01-17 11:43:45 +02:00

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require 'active_support/concern'
require 'active_support/descendants_tracker'
require 'active_support/core_ext/class/attribute'
require 'active_support/core_ext/kernel/reporting'
require 'active_support/core_ext/kernel/singleton_class'
require 'active_support/core_ext/object/inclusion'
module ActiveSupport
# \Callbacks are code hooks that are run at key points in an object's lifecycle.
# The typical use case is to have a base class define a set of callbacks relevant
# to the other functionality it supplies, so that subclasses can install callbacks
# that enhance or modify the base functionality without needing to override
# or redefine methods of the base class.
#
# Mixing in this module allows you to define the events in the object's lifecycle
# that will support callbacks (via +ClassMethods.define_callbacks+), set the instance
# methods, procs, or callback objects to be called (via +ClassMethods.set_callback+),
# and run the installed callbacks at the appropriate times (via +run_callbacks+).
#
# Three kinds of callbacks are supported: before callbacks, run before a certain event;
# after callbacks, run after the event; and around callbacks, blocks that surround the
# event, triggering it when they yield. Callback code can be contained in instance
# methods, procs or lambdas, or callback objects that respond to certain predetermined
# methods. See +ClassMethods.set_callback+ for details.
#
# ==== Example
#
# class Record
# include ActiveSupport::Callbacks
# define_callbacks :save
#
# def save
# run_callbacks :save do
# puts "- save"
# end
# end
# end
#
# class PersonRecord < Record
# set_callback :save, :before, :saving_message
# def saving_message
# puts "saving..."
# end
#
# set_callback :save, :after do |object|
# puts "saved"
# end
# end
#
# person = PersonRecord.new
# person.save
#
# Output:
# saving...
# - save
# saved
#
module Callbacks
extend Concern
included do
extend ActiveSupport::DescendantsTracker
end
# Runs the callbacks for the given event.
#
# Calls the before and around callbacks in the order they were set, yields
# the block (if given one), and then runs the after callbacks in reverse order.
# Optionally accepts a key, which will be used to compile an optimized callback
# method for each key. See +ClassMethods.define_callbacks+ for more information.
#
# If the callback chain was halted, returns +false+. Otherwise returns the result
# of the block, or +true+ if no block is given.
#
# run_callbacks :save do
# save
# end
#
def run_callbacks(kind, key = nil, &block)
self.class.__run_callbacks(key, kind, self, &block)
end
private
# A hook invoked everytime a before callback is halted.
# This can be overriden in AS::Callback implementors in order
# to provide better debugging/logging.
def halted_callback_hook(filter)
end
class Callback #:nodoc:#
@@_callback_sequence = 0
attr_accessor :chain, :filter, :kind, :options, :klass, :raw_filter
def initialize(chain, filter, kind, options, klass)
@chain, @kind, @klass = chain, kind, klass
normalize_options!(options)
@raw_filter, @options = filter, options
@filter = _compile_filter(filter)
@compiled_options = _compile_options(options)
@callback_id = next_id
end
def clone(chain, klass)
obj = super()
obj.chain = chain
obj.klass = klass
obj.options = @options.dup
obj.options[:if] = @options[:if].dup
obj.options[:unless] = @options[:unless].dup
obj
end
def normalize_options!(options)
options[:if] = Array(options[:if])
options[:unless] = Array(options[:unless])
options[:per_key] ||= {}
options[:if] += Array(options[:per_key][:if])
options[:unless] += Array(options[:per_key][:unless])
end
def name
chain.name
end
def next_id
@@_callback_sequence += 1
end
def matches?(_kind, _filter)
@kind == _kind && @filter == _filter
end
def _update_filter(filter_options, new_options)
filter_options[:if].push(new_options[:unless]) if new_options.key?(:unless)
filter_options[:unless].push(new_options[:if]) if new_options.key?(:if)
end
def recompile!(_options, _per_key)
_update_filter(self.options, _options)
_update_filter(self.options, _per_key)
@callback_id = next_id
@filter = _compile_filter(@raw_filter)
@compiled_options = _compile_options(@options)
end
# Wraps code with filter
def apply(code, key=nil, object=nil)
case @kind
when :before
<<-RUBY_EVAL
if !halted && #{@compiled_options}
# This double assignment is to prevent warnings in 1.9.3 as
# the `result` variable is not always used except if the
# terminator code refers to it.
result = result = #{@filter}
halted = (#{chain.config[:terminator]})
if halted
halted_callback_hook(#{@raw_filter.inspect.inspect})
end
end
#{code}
RUBY_EVAL
when :after
<<-RUBY_EVAL
#{code}
if #{@compiled_options}
#{@filter}
end
RUBY_EVAL
when :around
name = define_conditional_callback
<<-RUBY_EVAL
#{name}(halted) do
#{code}
value
end
RUBY_EVAL
end
end
private
# Compile around filters with conditions into proxy methods
# that contain the conditions.
#
# For `around_save :filter_name, :if => :condition':
#
# def _conditional_callback_save_17
# if condition
# filter_name do
# yield self
# end
# else
# yield self
# end
# end
#
def define_conditional_callback
name = "_conditional_callback_#{@kind}_#{next_id}"
@klass.class_eval <<-RUBY_EVAL, __FILE__, __LINE__ + 1
def #{name}(halted)
if #{@compiled_options} && !halted
#{@filter} do
yield self
end
else
yield self
end
end
RUBY_EVAL
name
end
# Options support the same options as filters themselves (and support
# symbols, string, procs, and objects), so compile a conditional
# expression based on the options
def _compile_options(options)
conditions = ["true"]
unless options[:if].empty?
conditions << Array(_compile_filter(options[:if]))
end
unless options[:unless].empty?
conditions << Array(_compile_filter(options[:unless])).map {|f| "!#{f}"}
end
conditions.flatten.join(" && ")
end
# Filters support:
#
# Arrays:: Used in conditions. This is used to specify
# multiple conditions. Used internally to
# merge conditions from skip_* filters
# Symbols:: A method to call
# Strings:: Some content to evaluate
# Procs:: A proc to call with the object
# Objects:: An object with a before_foo method on it to call
#
# All of these objects are compiled into methods and handled
# the same after this point:
#
# Arrays:: Merged together into a single filter
# Symbols:: Already methods
# Strings:: class_eval'ed into methods
# Procs:: define_method'ed into methods
# Objects::
# a method is created that calls the before_foo method
# on the object.
#
def _compile_filter(filter)
method_name = "_callback_#{@kind}_#{next_id}"
case filter
when Array
filter.map {|f| _compile_filter(f)}
when Symbol
filter
when String
"(#{filter})"
when Proc
@klass.send(:define_method, method_name, &filter)
return method_name if filter.arity <= 0
method_name << (filter.arity == 1 ? "(self)" : " self, Proc.new ")
else
@klass.send(:define_method, "#{method_name}_object") { filter }
_normalize_legacy_filter(kind, filter)
scopes = Array(chain.config[:scope])
method_to_call = scopes.map{ |s| s.is_a?(Symbol) ? send(s) : s }.join("_")
@klass.class_eval <<-RUBY_EVAL, __FILE__, __LINE__ + 1
def #{method_name}(&blk)
#{method_name}_object.send(:#{method_to_call}, self, &blk)
end
RUBY_EVAL
method_name
end
end
def _normalize_legacy_filter(kind, filter)
if !filter.respond_to?(kind) && filter.respond_to?(:filter)
filter.singleton_class.class_eval <<-RUBY_EVAL, __FILE__, __LINE__ + 1
def #{kind}(context, &block) filter(context, &block) end
RUBY_EVAL
elsif filter.respond_to?(:before) && filter.respond_to?(:after) && kind == :around
def filter.around(context)
should_continue = before(context)
yield if should_continue
after(context)
end
end
end
end
# An Array with a compile method
class CallbackChain < Array #:nodoc:#
attr_reader :name, :config
def initialize(name, config)
@name = name
@config = {
:terminator => "false",
:rescuable => false,
:scope => [ :kind ]
}.merge(config)
end
def compile(key=nil, object=nil)
method = []
method << "value = nil"
method << "halted = false"
callbacks = yielding
reverse_each do |callback|
callbacks = callback.apply(callbacks, key, object)
end
method << callbacks
method << "raise rescued_error if rescued_error" if config[:rescuable]
method << "halted ? false : (block_given? ? value : true)"
method.flatten.compact.join("\n")
end
# Returns part of method that evaluates the callback block
def yielding
method = []
if config[:rescuable]
method << "rescued_error = nil"
method << "begin"
end
method << "value = yield if block_given? && !halted"
if config[:rescuable]
method << "rescue Exception => e"
method << "rescued_error = e"
method << "end"
end
method.join("\n")
end
end
module ClassMethods
# This method calls the callback method for the given key.
# If this called first time it creates a new callback method for the key,
# calculating which callbacks can be omitted because of per_key conditions.
#
def __run_callbacks(key, kind, object, &blk) #:nodoc:
name = __callback_runner_name(key, kind)
unless object.respond_to?(name)
str = send("_#{kind}_callbacks").compile(key, object)
class_eval <<-RUBY_EVAL, __FILE__, __LINE__ + 1
def #{name}() #{str} end
protected :#{name}
RUBY_EVAL
end
object.send(name, &blk)
end
def __reset_runner(symbol)
name = __callback_runner_name(nil, symbol)
undef_method(name) if method_defined?(name)
end
def __callback_runner_name(key, kind)
"_run__#{self.name.hash.abs}__#{kind}__callbacks"
end
# This is used internally to append, prepend and skip callbacks to the
# CallbackChain.
#
def __update_callbacks(name, filters = [], block = nil) #:nodoc:
type = filters.first.in?([:before, :after, :around]) ? filters.shift : :before
options = filters.last.is_a?(Hash) ? filters.pop : {}
filters.unshift(block) if block
([self] + ActiveSupport::DescendantsTracker.descendants(self)).reverse.each do |target|
chain = target.send("_#{name}_callbacks")
yield target, chain.dup, type, filters, options
target.__reset_runner(name)
end
end
# Install a callback for the given event.
#
# set_callback :save, :before, :before_meth
# set_callback :save, :after, :after_meth, :if => :condition
# set_callback :save, :around, lambda { |r| stuff; result = yield; stuff }
#
# The second arguments indicates whether the callback is to be run +:before+,
# +:after+, or +:around+ the event. If omitted, +:before+ is assumed. This
# means the first example above can also be written as:
#
# set_callback :save, :before_meth
#
# The callback can specified as a symbol naming an instance method; as a proc,
# lambda, or block; as a string to be instance evaluated; or as an object that
# responds to a certain method determined by the <tt>:scope</tt> argument to
# +define_callback+.
#
# If a proc, lambda, or block is given, its body is evaluated in the context
# of the current object. It can also optionally accept the current object as
# an argument.
#
# Before and around callbacks are called in the order that they are set; after
# callbacks are called in the reverse order.
#
# Around callbacks can access the return value from the event, if it
# wasn't halted, from the +yield+ call.
#
# ===== Options
#
# * <tt>:if</tt> - A symbol naming an instance method or a proc; the callback
# will be called only when it returns a true value.
# * <tt>:unless</tt> - A symbol naming an instance method or a proc; the callback
# will be called only when it returns a false value.
# * <tt>:prepend</tt> - If true, the callback will be prepended to the existing
# chain rather than appended.
# * <tt>:per_key</tt> - A hash with <tt>:if</tt> and <tt>:unless</tt> options;
# see "Per-key conditions" below.
#
# ===== Per-key conditions
#
# When creating or skipping callbacks, you can specify conditions that
# are always the same for a given key. For instance, in Action Pack,
# we convert :only and :except conditions into per-key conditions.
#
# before_filter :authenticate, :except => "index"
#
# becomes
#
# set_callback :process_action, :before, :authenticate, :per_key => {:unless => proc {|c| c.action_name == "index"}}
#
# Per-key conditions are evaluated only once per use of a given key.
# In the case of the above example, you would do:
#
# run_callbacks(:process_action, action_name) { ... dispatch stuff ... }
#
# In that case, each action_name would get its own compiled callback
# method that took into consideration the per_key conditions. This
# is a speed improvement for ActionPack.
#
def set_callback(name, *filter_list, &block)
mapped = nil
__update_callbacks(name, filter_list, block) do |target, chain, type, filters, options|
mapped ||= filters.map do |filter|
Callback.new(chain, filter, type, options.dup, self)
end
filters.each do |filter|
chain.delete_if {|c| c.matches?(type, filter) }
end
options[:prepend] ? chain.unshift(*(mapped.reverse)) : chain.push(*mapped)
target.send("_#{name}_callbacks=", chain)
end
end
# Skip a previously set callback. Like +set_callback+, <tt>:if</tt> or <tt>:unless</tt>
# options may be passed in order to control when the callback is skipped.
#
# class Writer < Person
# skip_callback :validate, :before, :check_membership, :if => lambda { self.age > 18 }
# end
#
def skip_callback(name, *filter_list, &block)
__update_callbacks(name, filter_list, block) do |target, chain, type, filters, options|
filters.each do |filter|
filter = chain.find {|c| c.matches?(type, filter) }
if filter && options.any?
new_filter = filter.clone(chain, self)
chain.insert(chain.index(filter), new_filter)
new_filter.recompile!(options, options[:per_key] || {})
end
chain.delete(filter)
end
target.send("_#{name}_callbacks=", chain)
end
end
# Remove all set callbacks for the given event.
#
def reset_callbacks(symbol)
callbacks = send("_#{symbol}_callbacks")
ActiveSupport::DescendantsTracker.descendants(self).each do |target|
chain = target.send("_#{symbol}_callbacks").dup
callbacks.each { |c| chain.delete(c) }
target.send("_#{symbol}_callbacks=", chain)
target.__reset_runner(symbol)
end
self.send("_#{symbol}_callbacks=", callbacks.dup.clear)
__reset_runner(symbol)
end
# Define sets of events in the object lifecycle that support callbacks.
#
# define_callbacks :validate
# define_callbacks :initialize, :save, :destroy
#
# ===== Options
#
# * <tt>:terminator</tt> - Determines when a before filter will halt the callback
# chain, preventing following callbacks from being called and the event from being
# triggered. This is a string to be eval'ed. The result of the callback is available
# in the <tt>result</tt> variable.
#
# define_callbacks :validate, :terminator => "result == false"
#
# In this example, if any before validate callbacks returns +false+,
# other callbacks are not executed. Defaults to "false", meaning no value
# halts the chain.
#
# * <tt>:rescuable</tt> - By default, after filters are not executed if
# the given block or a before filter raises an error. By setting this option
# to <tt>true</tt> exception raised by given block is stored and after
# executing all the after callbacks the stored exception is raised.
#
# * <tt>:scope</tt> - Indicates which methods should be executed when an object
# is used as a callback.
#
# class Audit
# def before(caller)
# puts 'Audit: before is called'
# end
#
# def before_save(caller)
# puts 'Audit: before_save is called'
# end
# end
#
# class Account
# include ActiveSupport::Callbacks
#
# define_callbacks :save
# set_callback :save, :before, Audit.new
#
# def save
# run_callbacks :save do
# puts 'save in main'
# end
# end
# end
#
# In the above case whenever you save an account the method <tt>Audit#before</tt> will
# be called. On the other hand
#
# define_callbacks :save, :scope => [:kind, :name]
#
# would trigger <tt>Audit#before_save</tt> instead. That's constructed by calling
# <tt>#{kind}_#{name}</tt> on the given instance. In this case "kind" is "before" and
# "name" is "save". In this context +:kind+ and +:name+ have special meanings: +:kind+
# refers to the kind of callback (before/after/around) and +:name+ refers to the
# method on which callbacks are being defined.
#
# A declaration like
#
# define_callbacks :save, :scope => [:name]
#
# would call <tt>Audit#save</tt>.
#
def define_callbacks(*callbacks)
config = callbacks.last.is_a?(Hash) ? callbacks.pop : {}
callbacks.each do |callback|
class_attribute "_#{callback}_callbacks"
send("_#{callback}_callbacks=", CallbackChain.new(callback, config))
end
end
end
end
end
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