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Diffstat (limited to 'activerecord/lib/active_record/aggregations.rb')
| -rw-r--r-- | activerecord/lib/active_record/aggregations.rb | 261 |
1 files changed, 0 insertions, 261 deletions
diff --git a/activerecord/lib/active_record/aggregations.rb b/activerecord/lib/active_record/aggregations.rb deleted file mode 100644 index 3ae7030caa..0000000000 --- a/activerecord/lib/active_record/aggregations.rb +++ /dev/null @@ -1,261 +0,0 @@ -module ActiveRecord - # = Active Record Aggregations - module Aggregations # :nodoc: - extend ActiveSupport::Concern - - def clear_aggregation_cache #:nodoc: - @aggregation_cache.clear if persisted? - 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). - # - # 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 <=> other_money.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 with any other attribute: - # - # 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. - # - # customer.address_street = "Hyancintvej" - # customer.address_city = "Copenhagen" - # customer.address # => Address.new("Hyancintvej", "Copenhagen") - # - # customer.address_street = "Vesterbrogade" - # customer.address # => Address.new("Hyancintvej", "Copenhagen") - # customer.clear_aggregation_cache - # customer.address # => Address.new("Vesterbrogade", "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. The - # Money#exchange_to method is an example of this. It 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.where(:balance => Money.new(20, "USD")).all - # - 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 of the attribute in the value object. The - # order in which mappings are defined determines 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>. If <tt>:allow_nil</tt> is set to true, the converter - # can return nil to skip the assignment. - # - # 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 = {}) - 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] - - 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) - define_method(name) do - if @aggregation_cache[name].nil? && (!allow_nil || mapping.any? {|pair| !read_attribute(pair.first).nil? }) - attrs = mapping.collect {|pair| read_attribute(pair.first)} - object = constructor.respond_to?(:call) ? - constructor.call(*attrs) : - class_name.constantize.send(constructor, *attrs) - @aggregation_cache[name] = object - end - @aggregation_cache[name] - end - end - - def writer_method(name, class_name, mapping, allow_nil, converter) - define_method("#{name}=") do |part| - klass = class_name.constantize - unless part.is_a?(klass) || converter.nil? || part.nil? - part = converter.respond_to?(:call) ? converter.call(part) : klass.send(converter, part) - end - - if part.nil? && allow_nil - mapping.each { |pair| self[pair.first] = nil } - @aggregation_cache[name] = nil - else - mapping.each { |pair| self[pair.first] = part.send(pair.last) } - @aggregation_cache[name] = part.freeze - end - end - end - end - end -end |