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ensuring that documentation does not exceed 100 columns

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Neeraj Singh 2010-07-31 07:12:29 -04:00
parent 69b401220c
commit 6ac9482905
1 changed files with 65 additions and 51 deletions
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116
activerecord/lib/active_record/aggregations.rb
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@ -9,11 +9,13 @@ module ActiveRecord
end unless self.new_record? end unless self.new_record?
end 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+
# as value objects. It expresses relationships like "Account [is] composed of Money [among other things]" or "Person [is] # for representing attributes as value objects. It expresses relationships like "Account [is]
# composed of [an] address". Each call to the macro adds a description of how the value objects are created from the # composed of Money [among other things]" or "Person [is]
# 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
# and how it can be turned back into attributes (when the entity is saved to the database). Example: # 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 # class Customer < ActiveRecord::Base
# composed_of :balance, :class_name => "Money", :mapping => %w(balance amount) # composed_of :balance, :class_name => "Money", :mapping => %w(balance amount)
@ -68,9 +70,10 @@ module ActiveRecord
# end # end
# end # end
# #
# Now it's possible to access attributes from the database through the value objects instead. If you choose to name the # Now it's possible to access attributes from the database through the value objects instead. If
# composition the same as the attribute's name, it will be the only way to access that attribute. That's the case with our # you choose to name the composition the same as the attribute's name, it will be the only way to
# +balance+ attribute. You interact with the value objects just like you would any other attribute, though: # 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.new(20) # sets the Money value object and the attribute
# customer.balance # => Money value object # customer.balance # => Money value object
@ -79,8 +82,9 @@ module ActiveRecord
# customer.balance == Money.new(20) # => true # customer.balance == Money.new(20) # => true
# customer.balance < Money.new(5) # => false # 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 # Value objects can also be composed of multiple attributes, such as the case of Address. The order
# determine the order of the parameters. Example: # of the mappings will
# determine the order of the parameters.
# #
# customer.address_street = "Hyancintvej" # customer.address_street = "Hyancintvej"
# customer.address_city = "Copenhagen" # customer.address_city = "Copenhagen"
@ -91,38 +95,43 @@ module ActiveRecord
# #
# == Writing value objects # == Writing value objects
# #
# Value objects are immutable and interchangeable objects that represent a given value, such as a Money object representing # Value objects are immutable and interchangeable objects that represent a given value, such as
# $5. Two Money objects both representing $5 should be equal (through methods such as <tt>==</tt> and <tt><=></tt> from Comparable if ranking # a Money object representing $5. Two Money objects both representing $5 should be equal (through
# makes sense). This is unlike entity objects where equality is determined by identity. An entity class such as Customer can # methods such as <tt>==</tt> and <tt><=></tt> from Comparable if ranking makes sense). This is
# easily have two different objects that both have an address on Hyancintvej. Entity identity is determined by object or # unlike entity objects where equality is determined by identity. An entity class such as Customer can
# relational unique identifiers (such as primary keys). Normal ActiveRecord::Base classes are entity objects. # 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 # It's also important to treat the value objects as immutable. Don't allow the Money object to have
# creation. Create a new Money object with the new value instead. This is exemplified by the Money#exchange_to method that # its amount changed after creation. Create a new Money object with the new value instead. This
# returns a new value object instead of changing its own values. Active Record won't persist value objects that have been # is exemplified by the Money#exchange_to method that returns a new value object instead of changing
# changed through means other than the writer method. # 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
# change it afterwards will result in a ActiveSupport::FrozenObjectError. # 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 # Read more about value objects on http://c2.com/cgi/wiki?ValueObject and on the dangers of not
# immutable on http://c2.com/cgi/wiki?ValueObjectsShouldBeImmutable # keeping value objects immutable on http://c2.com/cgi/wiki?ValueObjectsShouldBeImmutable
# #
# == Custom constructors and converters # == 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 # By default value objects are initialized by calling the <tt>new</tt> constructor of the value
# mapped attributes, in the order specified by the <tt>:mapping</tt> option, as arguments. If the value class doesn't support # class passing each of the mapped attributes, in the order specified by the <tt>:mapping</tt>
# this convention then +composed_of+ allows a custom constructor to be specified. # 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 # When a new value is assigned to the value object the default assumption is that the new value
# class. Specifying a custom converter allows the new value to be automatically converted to an instance of value class if # is an instance of the value class. Specifying a custom converter allows the new value to be automatically
# necessary. # 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 # For example, the NetworkResource model has +network_address+ and +cidr_range+ attributes that
# NetAddr::CIDR value class (http://netaddr.rubyforge.org). The constructor for the value class is called +create+ and it # should be aggregated using the NetAddr::CIDR value class (http://netaddr.rubyforge.org). The constructor
# expects a CIDR address string as a parameter. New values can be assigned to the value object using either another # for the value class is called +create+ and it expects a CIDR address string as a parameter. New
# NetAddr::CIDR object, a string or an array. The <tt>:constructor</tt> and <tt>:converter</tt> options can be used to # values can be assigned to the value object using either another NetAddr::CIDR object, a string
# meet these requirements: # or an array. The <tt>:constructor</tt> and <tt>:converter</tt> options can be used to meet
# these requirements:
# #
# class NetworkResource < ActiveRecord::Base # class NetworkResource < ActiveRecord::Base
# composed_of :cidr, # composed_of :cidr,
@ -149,9 +158,9 @@ module ActiveRecord
# #
# == Finding records by a value object # == 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 # Once a +composed_of+ relationship is specified for a model, records can be loaded from the database
# of the value object in the conditions hash. The following example finds all customers with +balance_amount+ equal to 20 and # by specifying an instance of the value object in the conditions hash. The following example
# +balance_currency+ equal to "USD": # finds all customers with +balance_amount+ equal to 20 and +balance_currency+ equal to "USD":
# #
# Customer.find(:all, :conditions => {:balance => Money.new(20, "USD")}) # Customer.find(:all, :conditions => {:balance => Money.new(20, "USD")})
# #
@ -160,23 +169,28 @@ module ActiveRecord
# <tt>composed_of :address</tt> adds <tt>address</tt> and <tt>address=(new_address)</tt> methods. # <tt>composed_of :address</tt> adds <tt>address</tt> and <tt>address=(new_address)</tt> methods.
# #
# Options are: # Options are:
# * <tt>:class_name</tt> - Specifies 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
# from the part id. So <tt>composed_of :address</tt> will by default be linked to the Address class, but # can't be inferred from the part id. So <tt>composed_of :address</tt> will by default be linked
# if the real class name is CompanyAddress, you'll have to specify it with this option. # to the Address class, but if the real class name is CompanyAddress, you'll have to specify it
# * <tt>:mapping</tt> - Specifies the mapping of entity attributes to attributes of the value object. Each mapping # with this option.
# is represented as an array where the first item is the name of the entity attribute and the second item is the # * <tt>:mapping</tt> - Specifies the mapping of entity attributes to attributes of the value
# name the attribute in the value object. The order in which mappings are defined determine the order in which # object. Each mapping is represented as an array where the first item is the name of the
# attributes are sent to the value class constructor. # 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 # * <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. # attributes are +nil+. Setting the value object to +nil+ has the effect of writing +nil+ to all
# mapped attributes.
# This defaults to +false+. # This defaults to +false+.
# * <tt>:constructor</tt> - A symbol specifying the name of the constructor method or a Proc that is called to # * <tt>:constructor</tt> - A symbol specifying the name of the constructor method or a Proc that
# initialize the value object. The constructor is passed all of the mapped attributes, in the order that they # is called to initialize the value object. The constructor is passed all of the mapped attributes,
# are defined in the <tt>:mapping option</tt>, as arguments and uses them to instantiate a <tt>:class_name</tt> object. # 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>. # 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 # * <tt>:converter</tt> - A symbol specifying the name of a class method of <tt>:class_name</tt>
# called when a new value is assigned to the value object. The converter is passed the single value that is used # or a Proc that is called when a new value is assigned to the value object. The converter is
# in the assignment and is only called if the new value is not an instance of <tt>:class_name</tt>. # 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: # Option examples:
# composed_of :temperature, :mapping => %w(reading celsius) # composed_of :temperature, :mapping => %w(reading celsius)