diff options
Diffstat (limited to 'activerecord/lib/active_record/aggregations.rb')
| -rw-r--r-- | activerecord/lib/active_record/aggregations.rb | 144 |
1 files changed, 108 insertions, 36 deletions
diff --git a/activerecord/lib/active_record/aggregations.rb b/activerecord/lib/active_record/aggregations.rb index a5d3a50ef1..9eee7f2d98 100644 --- a/activerecord/lib/active_record/aggregations.rb +++ b/activerecord/lib/active_record/aggregations.rb @@ -10,10 +10,10 @@ module ActiveRecord end unless self.new_record? end - # Active Record implements aggregation through a macro-like class method called +composed_of+ for representing attributes + # 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) + # 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 @@ -30,10 +30,10 @@ module ActiveRecord # class Money # include Comparable # attr_reader :amount, :currency - # EXCHANGE_RATES = { "USD_TO_DKK" => 6 } - # - # def initialize(amount, currency = "USD") - # @amount, @currency = amount, currency + # EXCHANGE_RATES = { "USD_TO_DKK" => 6 } + # + # def initialize(amount, currency = "USD") + # @amount, @currency = amount, currency # end # # def exchange_to(other_currency) @@ -56,19 +56,19 @@ module ActiveRecord # # class Address # attr_reader :street, :city - # def initialize(street, city) - # @street, @city = street, city + # def initialize(street, city) + # @street, @city = street, city # end # - # def close_to?(other_address) - # city == other_address.city + # 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: @@ -87,8 +87,8 @@ module ActiveRecord # 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" + # customer.address_street # => "May Street" + # customer.address_city # => "Chicago" # # == Writing value objects # @@ -103,12 +103,51 @@ module ActiveRecord # 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 + # 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 @@ -122,47 +161,71 @@ module ActiveRecord # <tt>composed_of :address</tt> adds <tt>address</tt> and <tt>address=(new_address)</tt> methods. # # Options are: - # * <tt>:class_name</tt> - specify the class name of the association. Use it only if that name can't be inferred + # * <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 a number of mapping arrays (attribute, parameter) that bind an attribute name - # to a constructor parameter on the value class. - # * <tt>:allow_nil</tt> - specifies that the aggregate object will not be instantiated when all mapped - # attributes are +nil+. Setting the aggregate class to +nil+ has the effect of writing +nil+ to all mapped attributes. + # * <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+. - # - # An optional block can be passed to convert the argument that is passed to the writer method into an instance of - # <tt>:class_name</tt>. The block will only be called if the argument is not already an instance of <tt>:class_name</tt>. + # * <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)) {|balance| balance.to_money } + # 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) + 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 ] + 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 + 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) - reader_method(name, class_name, mapping, allow_nil) - writer_method(name, class_name, mapping, allow_nil, block) - create_reflection(:composed_of, part_id, options, self) end private - def reader_method(name, class_name, mapping, allow_nil) + 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? }) - instance_variable_set("@#{name}", class_name.constantize.new(*mapping.collect {|pair| read_attribute(pair.first)})) + 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 @@ -170,14 +233,23 @@ module ActiveRecord end - def writer_method(name, class_name, mapping, allow_nil, conversion) + 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 - part = conversion.call(part) unless part.is_a?(class_name.constantize) || conversion.nil? + 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 |