+++ /dev/null
-module ActiveRecord
- module Aggregations # :nodoc:
- def self.included(base)
- base.extend(ClassMethods)
- end
-
- def clear_aggregation_cache #:nodoc:
- self.class.reflect_on_all_aggregations.to_a.each do |assoc|
- instance_variable_set "@#{assoc.name}", nil
- end unless self.new_record?
- end
-
- # Active Record implements aggregation through a macro-like class method called +composed_of+ for representing attributes
- # as value objects. It expresses relationships like "Account [is] composed of Money [among other things]" or "Person [is]
- # composed of [an] address". Each call to the macro adds a description of how the value objects are created from the
- # attributes of the entity object (when the entity is initialized either as a new object or from finding an existing object)
- # and how it can be turned back into attributes (when the entity is saved to the database). Example:
- #
- # class Customer < ActiveRecord::Base
- # composed_of :balance, :class_name => "Money", :mapping => %w(balance amount)
- # composed_of :address, :mapping => [ %w(address_street street), %w(address_city city) ]
- # end
- #
- # The customer class now has the following methods to manipulate the value objects:
- # * <tt>Customer#balance, Customer#balance=(money)</tt>
- # * <tt>Customer#address, Customer#address=(address)</tt>
- #
- # These methods will operate with value objects like the ones described below:
- #
- # class Money
- # include Comparable
- # attr_reader :amount, :currency
- # EXCHANGE_RATES = { "USD_TO_DKK" => 6 }
- #
- # def initialize(amount, currency = "USD")
- # @amount, @currency = amount, currency
- # end
- #
- # def exchange_to(other_currency)
- # exchanged_amount = (amount * EXCHANGE_RATES["#{currency}_TO_#{other_currency}"]).floor
- # Money.new(exchanged_amount, other_currency)
- # end
- #
- # def ==(other_money)
- # amount == other_money.amount && currency == other_money.currency
- # end
- #
- # def <=>(other_money)
- # if currency == other_money.currency
- # amount <=> amount
- # else
- # amount <=> other_money.exchange_to(currency).amount
- # end
- # end
- # end
- #
- # class Address
- # attr_reader :street, :city
- # def initialize(street, city)
- # @street, @city = street, city
- # end
- #
- # def close_to?(other_address)
- # city == other_address.city
- # end
- #
- # def ==(other_address)
- # city == other_address.city && street == other_address.street
- # end
- # end
- #
- # Now it's possible to access attributes from the database through the value objects instead. If you choose to name the
- # composition the same as the attribute's name, it will be the only way to access that attribute. That's the case with our
- # +balance+ attribute. You interact with the value objects just like you would any other attribute, though:
- #
- # customer.balance = Money.new(20) # sets the Money value object and the attribute
- # customer.balance # => Money value object
- # customer.balance.exchange_to("DKK") # => Money.new(120, "DKK")
- # customer.balance > Money.new(10) # => true
- # customer.balance == Money.new(20) # => true
- # customer.balance < Money.new(5) # => false
- #
- # Value objects can also be composed of multiple attributes, such as the case of Address. The order of the mappings will
- # determine the order of the parameters. Example:
- #
- # customer.address_street = "Hyancintvej"
- # customer.address_city = "Copenhagen"
- # customer.address # => Address.new("Hyancintvej", "Copenhagen")
- # customer.address = Address.new("May Street", "Chicago")
- # customer.address_street # => "May Street"
- # customer.address_city # => "Chicago"
- #
- # == Writing value objects
- #
- # Value objects are immutable and interchangeable objects that represent a given value, such as a Money object representing
- # $5. Two Money objects both representing $5 should be equal (through methods such as <tt>==</tt> and <tt><=></tt> from Comparable if ranking
- # makes sense). This is unlike entity objects where equality is determined by identity. An entity class such as Customer can
- # easily have two different objects that both have an address on Hyancintvej. Entity identity is determined by object or
- # relational unique identifiers (such as primary keys). Normal ActiveRecord::Base classes are entity objects.
- #
- # It's also important to treat the value objects as immutable. Don't allow the Money object to have its amount changed after
- # creation. Create a new Money object with the new value instead. This is exemplified by the Money#exchange_to method that
- # returns a new value object instead of changing its own values. Active Record won't persist value objects that have been
- # changed through means other than the writer method.
- #
- # The immutable requirement is enforced by Active Record by freezing any object assigned as a value object. Attempting to
- # change it afterwards will result in a ActiveSupport::FrozenObjectError.
- #
- # Read more about value objects on http://c2.com/cgi/wiki?ValueObject and on the dangers of not keeping value objects
- # immutable on http://c2.com/cgi/wiki?ValueObjectsShouldBeImmutable
- #
- # == Custom constructors and converters
- #
- # By default value objects are initialized by calling the <tt>new</tt> constructor of the value class passing each of the
- # mapped attributes, in the order specified by the <tt>:mapping</tt> option, as arguments. If the value class doesn't support
- # this convention then +composed_of+ allows a custom constructor to be specified.
- #
- # When a new value is assigned to the value object the default assumption is that the new value is an instance of the value
- # class. Specifying a custom converter allows the new value to be automatically converted to an instance of value class if
- # necessary.
- #
- # For example, the NetworkResource model has +network_address+ and +cidr_range+ attributes that should be aggregated using the
- # NetAddr::CIDR value class (http://netaddr.rubyforge.org). The constructor for the value class is called +create+ and it
- # expects a CIDR address string as a parameter. New values can be assigned to the value object using either another
- # NetAddr::CIDR object, a string or an array. The <tt>:constructor</tt> and <tt>:converter</tt> options can be used to
- # meet these requirements:
- #
- # class NetworkResource < ActiveRecord::Base
- # composed_of :cidr,
- # :class_name => 'NetAddr::CIDR',
- # :mapping => [ %w(network_address network), %w(cidr_range bits) ],
- # :allow_nil => true,
- # :constructor => Proc.new { |network_address, cidr_range| NetAddr::CIDR.create("#{network_address}/#{cidr_range}") },
- # :converter => Proc.new { |value| NetAddr::CIDR.create(value.is_a?(Array) ? value.join('/') : value) }
- # end
- #
- # # This calls the :constructor
- # network_resource = NetworkResource.new(:network_address => '192.168.0.1', :cidr_range => 24)
- #
- # # These assignments will both use the :converter
- # network_resource.cidr = [ '192.168.2.1', 8 ]
- # network_resource.cidr = '192.168.0.1/24'
- #
- # # This assignment won't use the :converter as the value is already an instance of the value class
- # network_resource.cidr = NetAddr::CIDR.create('192.168.2.1/8')
- #
- # # Saving and then reloading will use the :constructor on reload
- # network_resource.save
- # network_resource.reload
- #
- # == Finding records by a value object
- #
- # Once a +composed_of+ relationship is specified for a model, records can be loaded from the database by specifying an instance
- # of the value object in the conditions hash. The following example finds all customers with +balance_amount+ equal to 20 and
- # +balance_currency+ equal to "USD":
- #
- # Customer.find(:all, :conditions => {:balance => Money.new(20, "USD")})
- #
- module ClassMethods
- # Adds reader and writer methods for manipulating a value object:
- # <tt>composed_of :address</tt> adds <tt>address</tt> and <tt>address=(new_address)</tt> methods.
- #
- # Options are:
- # * <tt>:class_name</tt> - Specifies the class name of the association. Use it only if that name can't be inferred
- # from the part id. So <tt>composed_of :address</tt> will by default be linked to the Address class, but
- # if the real class name is CompanyAddress, you'll have to specify it with this option.
- # * <tt>:mapping</tt> - Specifies the mapping of entity attributes to attributes of the value object. Each mapping
- # is represented as an array where the first item is the name of the entity attribute and the second item is the
- # name the attribute in the value object. The order in which mappings are defined determine the order in which
- # attributes are sent to the value class constructor.
- # * <tt>:allow_nil</tt> - Specifies that the value object will not be instantiated when all mapped
- # attributes are +nil+. Setting the value object to +nil+ has the effect of writing +nil+ to all mapped attributes.
- # This defaults to +false+.
- # * <tt>:constructor</tt> - A symbol specifying the name of the constructor method or a Proc that is called to
- # initialize the value object. The constructor is passed all of the mapped attributes, in the order that they
- # are defined in the <tt>:mapping option</tt>, as arguments and uses them to instantiate a <tt>:class_name</tt> object.
- # The default is <tt>:new</tt>.
- # * <tt>:converter</tt> - A symbol specifying the name of a class method of <tt>:class_name</tt> or a Proc that is
- # called when a new value is assigned to the value object. The converter is passed the single value that is used
- # in the assignment and is only called if the new value is not an instance of <tt>:class_name</tt>.
- #
- # Option examples:
- # composed_of :temperature, :mapping => %w(reading celsius)
- # composed_of :balance, :class_name => "Money", :mapping => %w(balance amount), :converter => Proc.new { |balance| balance.to_money }
- # composed_of :address, :mapping => [ %w(address_street street), %w(address_city city) ]
- # composed_of :gps_location
- # composed_of :gps_location, :allow_nil => true
- # composed_of :ip_address,
- # :class_name => 'IPAddr',
- # :mapping => %w(ip to_i),
- # :constructor => Proc.new { |ip| IPAddr.new(ip, Socket::AF_INET) },
- # :converter => Proc.new { |ip| ip.is_a?(Integer) ? IPAddr.new(ip, Socket::AF_INET) : IPAddr.new(ip.to_s) }
- #
- def composed_of(part_id, options = {}, &block)
- options.assert_valid_keys(:class_name, :mapping, :allow_nil, :constructor, :converter)
-
- name = part_id.id2name
- class_name = options[:class_name] || name.camelize
- mapping = options[:mapping] || [ name, name ]
- mapping = [ mapping ] unless mapping.first.is_a?(Array)
- allow_nil = options[:allow_nil] || false
- constructor = options[:constructor] || :new
- converter = options[:converter] || block
-
- ActiveSupport::Deprecation.warn('The conversion block has been deprecated, use the :converter option instead.', caller) if block_given?
-
- reader_method(name, class_name, mapping, allow_nil, constructor)
- writer_method(name, class_name, mapping, allow_nil, converter)
-
- create_reflection(:composed_of, part_id, options, self)
- end
-
- private
- def reader_method(name, class_name, mapping, allow_nil, constructor)
- module_eval do
- define_method(name) do |*args|
- force_reload = args.first || false
- if (instance_variable_get("@#{name}").nil? || force_reload) && (!allow_nil || mapping.any? {|pair| !read_attribute(pair.first).nil? })
- attrs = mapping.collect {|pair| read_attribute(pair.first)}
- object = case constructor
- when Symbol
- class_name.constantize.send(constructor, *attrs)
- when Proc, Method
- constructor.call(*attrs)
- else
- raise ArgumentError, 'Constructor must be a symbol denoting the constructor method to call or a Proc to be invoked.'
- end
- instance_variable_set("@#{name}", object)
- end
- instance_variable_get("@#{name}")
- end
- end
-
- end
-
- def writer_method(name, class_name, mapping, allow_nil, converter)
- module_eval do
- define_method("#{name}=") do |part|
- if part.nil? && allow_nil
- mapping.each { |pair| self[pair.first] = nil }
- instance_variable_set("@#{name}", nil)
- else
- unless part.is_a?(class_name.constantize) || converter.nil?
- part = case converter
- when Symbol
- class_name.constantize.send(converter, part)
- when Proc, Method
- converter.call(part)
- else
- raise ArgumentError, 'Converter must be a symbol denoting the converter method to call or a Proc to be invoked.'
- end
- end
- mapping.each { |pair| self[pair.first] = part.send(pair.last) }
- instance_variable_set("@#{name}", part.freeze)
- end
- end
- end
- end
- end
- end
-end
projects / feedcatcher.git / blobdiff