Active Record 源码阅读

根据ActiveRecord::Base里的继承链向上阅读

module ActiveRecord #:nodoc:
  class Base
    extend ActiveModel::Naming

    extend ActiveSupport::Benchmarkable
    extend ActiveSupport::DescendantsTracker

    extend ConnectionHandling
    extend QueryCache::ClassMethods
    extend Querying
    extend Translation
    extend DynamicMatchers
    extend Explain
    extend Enum
    extend Delegation::DelegateCache
    extend Aggregations::ClassMethods

    include Core
    include Persistence
    include ReadonlyAttributes
    include ModelSchema
    include Inheritance
    include Scoping
    include Sanitization
    include AttributeAssignment
    include ActiveModel::Conversion
    include Integration
    include Validations
    include CounterCache
    include Attributes
    include AttributeDecorators
    include Locking::Optimistic
    include Locking::Pessimistic
    include DefineCallbacks
    include AttributeMethods
    include Callbacks
    include Timestamp
    include Associations
    include ActiveModel::SecurePassword
    include AutosaveAssociation
    include NestedAttributes
    include Transactions
    include TouchLater
    include NoTouching
    include Reflection
    include Serialization
    include Store
    include SecureToken
    include Suppressor
  end

  ActiveSupport.run_load_hooks(:active_record, Base)
end

ActiveRecord::Suppressor

先是Suppressor，先看功能部分：

order = Order.last
Order.suppress do
  order.update(phone_number: "1xxxxxxxxxx")
end
order #=> phone_number 并没有被保存到数据库

被suppress（抑制）包裹的持久化语句将不会执行save操作。

module Suppressor
    extend ActiveSupport::Concern

    module ClassMethods
      def suppress(&block)
        previous_state = SuppressorRegistry.suppressed[name]
        SuppressorRegistry.suppressed[name] = true
        yield
      ensure
        SuppressorRegistry.suppressed[name] = previous_state
      end
    end

    def save(*) # :nodoc:
      SuppressorRegistry.suppressed[self.class.name] ? true : super
    end

    def save!(*) # :nodoc:
      SuppressorRegistry.suppressed[self.class.name] ? true : super
    end
  end

  class SuppressorRegistry # :nodoc:
    extend ActiveSupport::PerThreadRegistry

    attr_reader :suppressed

    def initialize
      @suppressed = {}
    end
  end
end

关于ActiveSupport::PerThreadRegistry可以看这里.

ActiveRecord::SecureToken

定义了随机生成token的，并保存到相应字段的功能。

# frozen_string_literal: true

module ActiveRecord
  module SecureToken
    extend ActiveSupport::Concern

    module ClassMethods
      # Example using #has_secure_token
      #
      #   # Schema: User(token:string, auth_token:string)
      #   class User < ActiveRecord::Base
      #     has_secure_token
      #     has_secure_token :auth_token
      #   end
      #
      #   user = User.new
      #   user.save
      #   user.token # => "pX27zsMN2ViQKta1bGfLmVJE"
      #   user.auth_token # => "77TMHrHJFvFDwodq8w7Ev2m7"
      #   user.regenerate_token # => true
      #   user.regenerate_auth_token # => true
      #
      # SecureRandom::base58 is used to generate the 24-character unique token, so collisions are highly unlikely.
      #
      # Note that it's still possible to generate a race condition in the database in the same way that
      # {validates_uniqueness_of}[rdoc-ref:Validations::ClassMethods#validates_uniqueness_of] can.
      # You're encouraged to add a unique index in the database to deal with this even more unlikely scenario.
      def has_secure_token(attribute = :token)
        # Load securerandom only when has_secure_token is used.
        require "active_support/core_ext/securerandom"
        define_method("regenerate_#{attribute}") { update! attribute => self.class.generate_unique_secure_token }
        before_create { send("#{attribute}=", self.class.generate_unique_secure_token) unless send("#{attribute}?") }
      end

      def generate_unique_secure_token
        SecureRandom.base58(24)
      end
    end
  end
end

ActiveRecord::Store

实现对一个字段的序列化。可参考。

require "active_support/core_ext/hash/indifferent_access"

module ActiveRecord
  module Store
    extend ActiveSupport::Concern

    included do
      class << self
        attr_accessor :local_stored_attributes
      end
    end

    module ClassMethods
      def store(store_attribute, options = {})
        serialize store_attribute, IndifferentCoder.new(store_attribute, options[:coder])
        store_accessor(store_attribute, options[:accessors], options.slice(:prefix, :suffix)) if options.has_key? :accessors
      end

      def store_accessor(store_attribute, *keys, prefix: nil, suffix: nil)
        keys = keys.flatten

        accessor_prefix =
          case prefix
          when String, Symbol
            "#{prefix}_"
          when TrueClass
            "#{store_attribute}_"
          else
            ""
          end
        accessor_suffix =
          case suffix
          when String, Symbol
            "_#{suffix}"
          when TrueClass
            "_#{store_attribute}"
          else
            ""
          end

        _store_accessors_module.module_eval do
          keys.each do |key|
            accessor_key = "#{accessor_prefix}#{key}#{accessor_suffix}"

            define_method("#{accessor_key}=") do |value|
              write_store_attribute(store_attribute, key, value)
            end

            define_method(accessor_key) do
              read_store_attribute(store_attribute, key)
            end

            define_method("#{accessor_key}_changed?") do
              return false unless attribute_changed?(store_attribute)
              prev_store, new_store = changes[store_attribute]
              prev_store&.dig(key) != new_store&.dig(key)
            end

            define_method("#{accessor_key}_change") do
              return unless attribute_changed?(store_attribute)
              prev_store, new_store = changes[store_attribute]
              [prev_store&.dig(key), new_store&.dig(key)]
            end

            define_method("#{accessor_key}_was") do
              return unless attribute_changed?(store_attribute)
              prev_store, _new_store = changes[store_attribute]
              prev_store&.dig(key)
            end

            define_method("saved_change_to_#{accessor_key}?") do
              return false unless saved_change_to_attribute?(store_attribute)
              prev_store, new_store = saved_change_to_attribute(store_attribute)
              prev_store&.dig(key) != new_store&.dig(key)
            end

            define_method("saved_change_to_#{accessor_key}") do
              return unless saved_change_to_attribute?(store_attribute)
              prev_store, new_store = saved_change_to_attribute(store_attribute)
              [prev_store&.dig(key), new_store&.dig(key)]
            end

            define_method("#{accessor_key}_before_last_save") do
              return unless saved_change_to_attribute?(store_attribute)
              prev_store, _new_store = saved_change_to_attribute(store_attribute)
              prev_store&.dig(key)
            end
          end
        end

        # assign new store attribute and create new hash to ensure that each class in the hierarchy
        # has its own hash of stored attributes.
        self.local_stored_attributes ||= {}
        self.local_stored_attributes[store_attribute] ||= []
        self.local_stored_attributes[store_attribute] |= keys
      end

      def _store_accessors_module # :nodoc:
        @_store_accessors_module ||= begin
          mod = Module.new
          include mod
          mod
        end
      end

      def stored_attributes
        parent = superclass.respond_to?(:stored_attributes) ? superclass.stored_attributes : {}
        if local_stored_attributes
          parent.merge!(local_stored_attributes) { |k, a, b| a | b }
        end
        parent
      end
    end

    private
      def read_store_attribute(store_attribute, key) # :doc:
        accessor = store_accessor_for(store_attribute)
        accessor.read(self, store_attribute, key)
      end

      def write_store_attribute(store_attribute, key, value) # :doc:
        accessor = store_accessor_for(store_attribute)
        accessor.write(self, store_attribute, key, value)
      end

      def store_accessor_for(store_attribute)
        type_for_attribute(store_attribute).accessor
      end

      class HashAccessor # :nodoc:
        def self.read(object, attribute, key)
          prepare(object, attribute)
          object.public_send(attribute)[key]
        end

        def self.write(object, attribute, key, value)
          prepare(object, attribute)
          if value != read(object, attribute, key)
            object.public_send :"#{attribute}_will_change!"
            object.public_send(attribute)[key] = value
          end
        end

        def self.prepare(object, attribute)
          object.public_send :"#{attribute}=", {} unless object.send(attribute)
        end
      end

      class StringKeyedHashAccessor < HashAccessor # :nodoc:
        def self.read(object, attribute, key)
          super object, attribute, key.to_s
        end

        def self.write(object, attribute, key, value)
          super object, attribute, key.to_s, value
        end
      end

      class IndifferentHashAccessor < ActiveRecord::Store::HashAccessor # :nodoc:
        def self.prepare(object, store_attribute)
          attribute = object.send(store_attribute)
          unless attribute.is_a?(ActiveSupport::HashWithIndifferentAccess)
            attribute = IndifferentCoder.as_indifferent_hash(attribute)
            object.send :"#{store_attribute}=", attribute
          end
          attribute
        end
      end

      class IndifferentCoder # :nodoc:
        def initialize(attr_name, coder_or_class_name)
          @coder =
            if coder_or_class_name.respond_to?(:load) && coder_or_class_name.respond_to?(:dump)
              coder_or_class_name
            else
              ActiveRecord::Coders::YAMLColumn.new(attr_name, coder_or_class_name || Object)
            end
        end

        def dump(obj)
          @coder.dump self.class.as_indifferent_hash(obj)
        end

        def load(yaml)
          self.class.as_indifferent_hash(@coder.load(yaml || ""))
        end

        def self.as_indifferent_hash(obj)
          case obj
          when ActiveSupport::HashWithIndifferentAccess
            obj
          when Hash
            obj.with_indifferent_access
          else
            ActiveSupport::HashWithIndifferentAccess.new
          end
        end
      end
  end
end

ActiveRecord::Reflection

用于保存Model的associations和aggregations的配置自信息.参考

ActiveRecord::NoTouching

实现在一个block里暂时禁用掉touch功能。参考

ActiveRecord::TouchLater

touch_later实现在一个事物里先执行别的语句之后，在commit之前执行touch的功能模块。

ActiveRecord:Transaction

事务模块的实现。参考

ActiveRecord::NestedAttributes

nested_attributes的实现。参考