/activerecord/lib/active_record/base.rb

begin
  require 'psych'
rescue LoadError
end

require 'yaml'
require 'set'
require 'active_support/benchmarkable'
require 'active_support/dependencies'
require 'active_support/descendants_tracker'
require 'active_support/time'
require 'active_support/core_ext/class/attribute'
require 'active_support/core_ext/class/attribute_accessors'
require 'active_support/core_ext/class/delegating_attributes'
require 'active_support/core_ext/class/attribute'
require 'active_support/core_ext/array/extract_options'
require 'active_support/core_ext/hash/deep_merge'
require 'active_support/core_ext/hash/indifferent_access'
require 'active_support/core_ext/hash/slice'
require 'active_support/core_ext/string/behavior'
require 'active_support/core_ext/kernel/singleton_class'
require 'active_support/core_ext/module/delegation'
require 'active_support/core_ext/module/introspection'
require 'active_support/core_ext/object/duplicable'
require 'active_support/core_ext/object/blank'
require 'arel'
require 'active_record/errors'
require 'active_record/log_subscriber'

module ActiveRecord #:nodoc:
  # = Active Record
  #
  # Active Record objects don't specify their attributes directly, but rather infer them from
  # the table definition with which they're linked. Adding, removing, and changing attributes
  # and their type is done directly in the database. Any change is instantly reflected in the
  # Active Record objects. The mapping that binds a given Active Record class to a certain
  # database table will happen automatically in most common cases, but can be overwritten for the uncommon ones.
  #
  # See the mapping rules in table_name and the full example in link:files/activerecord/README_rdoc.html for more insight.
  #
  # == Creation
  #
  # Active Records accept constructor parameters either in a hash or as a block. The hash
  # method is especially useful when you're receiving the data from somewhere else, like an
  # HTTP request. It works like this:
  #
  #   user = User.new(:name => "David", :occupation => "Code Artist")
  #   user.name # => "David"
  #
  # You can also use block initialization:
  #
  #   user = User.new do |u|
  #     u.name = "David"
  #     u.occupation = "Code Artist"
  #   end
  #
  # And of course you can just create a bare object and specify the attributes after the fact:
  #
  #   user = User.new
  #   user.name = "David"
  #   user.occupation = "Code Artist"
  #
  # == Conditions
  #
  # Conditions can either be specified as a string, array, or hash representing the WHERE-part of an SQL statement.
  # The array form is to be used when the condition input is tainted and requires sanitization. The string form can
  # be used for statements that don't involve tainted data. The hash form works much like the array form, except
  # only equality and range is possible. Examples:
  #
  #   class User < ActiveRecord::Base
  #     def self.authenticate_unsafely(user_name, password)
  #       where("user_name = '#{user_name}' AND password = '#{password}'").first
  #     end
  #
  #     def self.authenticate_safely(user_name, password)
  #       where("user_name = ? AND password = ?", user_name, password).first
  #     end
  #
  #     def self.authenticate_safely_simply(user_name, password)
  #       where(:user_name => user_name, :password => password).first
  #     end
  #   end
  #
  # The <tt>authenticate_unsafely</tt> method inserts the parameters directly into the query
  # and is thus susceptible to SQL-injection attacks if the <tt>user_name</tt> and +password+
  # parameters come directly from an HTTP request. The <tt>authenticate_safely</tt> and
  # <tt>authenticate_safely_simply</tt> both will sanitize the <tt>user_name</tt> and +password+
  # before inserting them in the query, which will ensure that an attacker can't escape the
  # query and fake the login (or worse).
  #
  # When using multiple parameters in the conditions, it can easily become hard to read exactly
  # what the fourth or fifth question mark is supposed to represent. In those cases, you can
  # resort to named bind variables instead. That's done by replacing the question marks with
  # symbols and supplying a hash with values for the matching symbol keys:
  #
  #   Company.where(
  #     "id = :id AND name = :name AND division = :division AND created_at > :accounting_date",
  #     { :id => 3, :name => "37signals", :division => "First", :accounting_date => '2005-01-01' }
  #   ).first
  #
  # Similarly, a simple hash without a statement will generate conditions based on equality with the SQL AND
  # operator. For instance:
  #
  #   Student.where(:first_name => "Harvey", :status => 1)
  #   Student.where(params[:student])
  #
  # A range may be used in the hash to use the SQL BETWEEN operator:
  #
  #   Student.where(:grade => 9..12)
  #
  # An array may be used in the hash to use the SQL IN operator:
  #
  #   Student.where(:grade => [9,11,12])
  #
  # When joining tables, nested hashes or keys written in the form 'table_name.column_name'
  # can be used to qualify the table name of a particular condition. For instance:
  #
  #   Student.joins(:schools).where(:schools => { :type => 'public' })
  #   Student.joins(:schools).where('schools.type' => 'public' )
  #
  # == Overwriting default accessors
  #
  # All column values are automatically available through basic accessors on the Active Record
  # object, but sometimes you want to specialize this behavior. This can be done by overwriting
  # the default accessors (using the same name as the attribute) and calling
  # <tt>read_attribute(attr_name)</tt> and <tt>write_attribute(attr_name, value)</tt> to actually
  # change things.
  #
  #   class Song < ActiveRecord::Base
  #     # Uses an integer of seconds to hold the length of the song
  #
  #     def length=(minutes)
  #       write_attribute(:length, minutes.to_i * 60)
  #     end
  #
  #     def length
  #       read_attribute(:length) / 60
  #     end
  #   end
  #
  # You can alternatively use <tt>self[:attribute]=(value)</tt> and <tt>self[:attribute]</tt>
  # instead of <tt>write_attribute(:attribute, value)</tt> and <tt>read_attribute(:attribute)</tt>.
  #
  # == Attribute query methods
  #
  # In addition to the basic accessors, query methods are also automatically available on the Active Record object.
  # Query methods allow you to test whether an attribute value is present.
  #
  # For example, an Active Record User with the <tt>name</tt> attribute has a <tt>name?</tt> method that you can call
  # to determine whether the user has a name:
  #
  #   user = User.new(:name => "David")
  #   user.name? # => true
  #
  #   anonymous = User.new(:name => "")
  #   anonymous.name? # => false
  #
  # == Accessing attributes before they have been typecasted
  #
  # Sometimes you want to be able to read the raw attribute data without having the column-determined
  # typecast run its course first. That can be done by using the <tt><attribute>_before_type_cast</tt>
  # accessors that all attributes have. For example, if your Account model has a <tt>balance</tt> attribute,
  # you can call <tt>account.balance_before_type_cast</tt> or <tt>account.id_before_type_cast</tt>.
  #
  # This is especially useful in validation situations where the user might supply a string for an
  # integer field and you want to display the original string back in an error message. Accessing the
  # attribute normally would typecast the string to 0, which isn't what you want.
  #
  # == Dynamic attribute-based finders
  #
  # Dynamic attribute-based finders are a cleaner way of getting (and/or creating) objects
  # by simple queries without turning to SQL. They work by appending the name of an attribute
  # to <tt>find_by_</tt>, <tt>find_last_by_</tt>, or <tt>find_all_by_</tt> and thus produces finders
  # like <tt>Person.find_by_user_name</tt>, <tt>Person.find_all_by_last_name</tt>, and
  # <tt>Payment.find_by_transaction_id</tt>. Instead of writing
  # <tt>Person.where(:user_name => user_name).first</tt>, you just do <tt>Person.find_by_user_name(user_name)</tt>.
  # And instead of writing <tt>Person.where(:last_name => last_name).all</tt>, you just do
  # <tt>Person.find_all_by_last_name(last_name)</tt>.
  #
  # It's possible to add an exclamation point (!) on the end of the dynamic finders to get them to raise an
  # <tt>ActiveRecord::RecordNotFound</tt> error if they do not return any records,
  # like <tt>Person.find_by_last_name!</tt>.
  #
  # It's also possible to use multiple attributes in the same find by separating them with "_and_".
  #
  #  Person.where(:user_name => user_name, :password => password).first
  #  Person.find_by_user_name_and_password(user_name, password) # with dynamic finder
  #
  # It's even possible to call these dynamic finder methods on relations and named scopes.
  #
  #   Payment.order("created_on").find_all_by_amount(50)
  #   Payment.pending.find_last_by_amount(100)
  #
  # The same dynamic finder style can be used to create the object if it doesn't already exist.
  # This dynamic finder is called with <tt>find_or_create_by_</tt> and will return the object if
  # it already exists and otherwise creates it, then returns it. Protected attributes won't be set
  # unless they are given in a block.
  #
  #   # No 'Summer' tag exists
  #   Tag.find_or_create_by_name("Summer") # equal to Tag.create(:name => "Summer")
  #
  #   # Now the 'Summer' tag does exist
  #   Tag.find_or_create_by_name("Summer") # equal to Tag.find_by_name("Summer")
  #
  #   # Now 'Bob' exist and is an 'admin'
  #   User.find_or_create_by_name('Bob', :age => 40) { |u| u.admin = true }
  #
  # Use the <tt>find_or_initialize_by_</tt> finder if you want to return a new record without
  # saving it first. Protected attributes won't be set unless they are given in a block.
  #
  #   # No 'Winter' tag exists
  #   winter = Tag.find_or_initialize_by_name("Winter")
  #   winter.persisted? # false
  #
  # To find by a subset of the attributes to be used for instantiating a new object, pass a hash instead of
  # a list of parameters.
  #
  #   Tag.find_or_create_by_name(:name => "rails", :creator => current_user)
  #
  # That will either find an existing tag named "rails", or create a new one while setting the
  # user that created it.
  #
  # Just like <tt>find_by_*</tt>, you can also use <tt>scoped_by_*</tt> to retrieve data. The good thing about
  # using this feature is that the very first time result is returned using <tt>method_missing</tt> technique
  # but after that the method is declared on the class. Henceforth <tt>method_missing</tt> will not be hit.
  #
  #  User.scoped_by_user_name('David')
  #
  # == Saving arrays, hashes, and other non-mappable objects in text columns
  #
  # Active Record can serialize any object in text columns using YAML. To do so, you must
  # specify this with a call to the class method +serialize+.
  # This makes it possible to store arrays, hashes, and other non-mappable objects without doing
  # any additional work.
  #
  #   class User < ActiveRecord::Base
  #     serialize :preferences
  #   end
  #
  #   user = User.create(:preferences => { "background" => "black", "display" => large })
  #   User.find(user.id).preferences # => { "background" => "black", "display" => large }
  #
  # You can also specify a class option as the second parameter that'll raise an exception
  # if a serialized object is retrieved as a descendant of a class not in the hierarchy.
  #
  #   class User < ActiveRecord::Base
  #     serialize :preferences, Hash
  #   end
  #
  #   user = User.create(:preferences => %w( one two three ))
  #   User.find(user.id).preferences    # raises SerializationTypeMismatch
  #
  # When you specify a class option, the default value for that attribute will be a new
  # instance of that class.
  #
  #   class User < ActiveRecord::Base
  #     serialize :preferences, OpenStruct
  #   end
  #
  #   user = User.new
  #   user.preferences.theme_color = "red"
  #
  #
  # == Single table inheritance
  #
  # Active Record allows inheritance by storing the name of the class in a column that by
  # default is named "type" (can be changed by overwriting <tt>Base.inheritance_column</tt>).
  # This means that an inheritance looking like this:
  #
  #   class Company < ActiveRecord::Base; end
  #   class Firm < Company; end
  #   class Client < Company; end
  #   class PriorityClient < Client; end
  #
  # When you do <tt>Firm.create(:name => "37signals")</tt>, this record will be saved in
  # the companies table with type = "Firm". You can then fetch this row again using
  # <tt>Company.where(:name => '37signals').first</tt> and it will return a Firm object.
  #
  # If you don't have a type column defined in your table, single-table inheritance won't
  # be triggered. In that case, it'll work just like normal subclasses with no special magic
  # for differentiating between them or reloading the right type with find.
  #
  # Note, all the attributes for all the cases are kept in the same table. Read more:
  # http://www.martinfowler.com/eaaCatalog/singleTableInheritance.html
  #
  # == Connection to multiple databases in different models
  #
  # Connections are usually created through ActiveRecord::Base.establish_connection and retrieved
  # by ActiveRecord::Base.connection. All classes inheriting from ActiveRecord::Base will use this
  # connection. But you can also set a class-specific connection. For example, if Course is an
  # ActiveRecord::Base, but resides in a different database, you can just say <tt>Course.establish_connection</tt>
  # and Course and all of its subclasses will use this connection instead.
  #
  # This feature is implemented by keeping a connection pool in ActiveRecord::Base that is
  # a Hash indexed by the class. If a connection is requested, the retrieve_connection method
  # will go up the class-hierarchy until a connection is found in the connection pool.
  #
  # == Exceptions
  #
  # * ActiveRecordError - Generic error class and superclass of all other errors raised by Active Record.
  # * AdapterNotSpecified - The configuration hash used in <tt>establish_connection</tt> didn't include an
  #   <tt>:adapter</tt> key.
  # * AdapterNotFound - The <tt>:adapter</tt> key used in <tt>establish_connection</tt> specified a
  #   non-existent adapter
  #   (or a bad spelling of an existing one).
  # * AssociationTypeMismatch - The object assigned to the association wasn't of the type
  #   specified in the association definition.
  # * SerializationTypeMismatch - The serialized object wasn't of the class specified as the second parameter.
  # * ConnectionNotEstablished+ - No connection has been established. Use <tt>establish_connection</tt>
  #   before querying.
  # * RecordNotFound - No record responded to the +find+ method. Either the row with the given ID doesn't exist
  #   or the row didn't meet the additional restrictions. Some +find+ calls do not raise this exception to signal
  #   nothing was found, please check its documentation for further details.
  # * StatementInvalid - The database server rejected the SQL statement. The precise error is added in the message.
  # * MultiparameterAssignmentErrors - Collection of errors that occurred during a mass assignment using the
  #   <tt>attributes=</tt> method. The +errors+ property of this exception contains an array of
  #   AttributeAssignmentError
  #   objects that should be inspected to determine which attributes triggered the errors.
  # * AttributeAssignmentError - An error occurred while doing a mass assignment through the
  #   <tt>attributes=</tt> method.
  #   You can inspect the +attribute+ property of the exception object to determine which attribute
  #   triggered the error.
  #
  # *Note*: The attributes listed are class-level attributes (accessible from both the class and instance level).
  # So it's possible to assign a logger to the class through <tt>Base.logger=</tt> which will then be used by all
  # instances in the current object space.
  class Base
    ##
    # :singleton-method:
    # Accepts a logger conforming to the interface of Log4r or the default Ruby 1.8+ Logger class,
    # which is then passed on to any new database connections made and which can be retrieved on both
    # a class and instance level by calling +logger+.
    cattr_accessor :logger, :instance_writer => false

    ##
    # :singleton-method:
    # Contains the database configuration - as is typically stored in config/database.yml -
    # as a Hash.
    #
    # For example, the following database.yml...
    #
    #   development:
    #     adapter: sqlite3
    #     database: db/development.sqlite3
    #
    #   production:
    #     adapter: sqlite3
    #     database: db/production.sqlite3
    #
    # ...would result in ActiveRecord::Base.configurations to look like this:
    #
    #   {
    #      'development' => {
    #         'adapter'  => 'sqlite3',
    #         'database' => 'db/development.sqlite3'
    #      },
    #      'production' => {
    #         'adapter'  => 'sqlite3',
    #         'database' => 'db/production.sqlite3'
    #      }
    #   }
    cattr_accessor :configurations, :instance_writer => false
    @@configurations = {}

    ##
    # :singleton-method:
    # Accessor for the prefix type that will be prepended to every primary key column name.
    # The options are :table_name and :table_name_with_underscore. If the first is specified,
    # the Product class will look for "productid" instead of "id" as the primary column. If the
    # latter is specified, the Product class will look for "product_id" instead of "id". Remember
    # that this is a global setting for all Active Records.
    cattr_accessor :primary_key_prefix_type, :instance_writer => false
    @@primary_key_prefix_type = nil

    ##
    # :singleton-method:
    # Accessor for the name of the prefix string to prepend to every table name. So if set
    # to "basecamp_", all table names will be named like "basecamp_projects", "basecamp_people",
    # etc. This is a convenient way of creating a namespace for tables in a shared database.
    # By default, the prefix is the empty string.
    #
    # If you are organising your models within modules you can add a prefix to the models within
    # a namespace by defining a singleton method in the parent module called table_name_prefix which
    # returns your chosen prefix.
    class_attribute :table_name_prefix, :instance_writer => false
    self.table_name_prefix = ""

    ##
    # :singleton-method:
    # Works like +table_name_prefix+, but appends instead of prepends (set to "_basecamp" gives "projects_basecamp",
    # "people_basecamp"). By default, the suffix is the empty string.
    class_attribute :table_name_suffix, :instance_writer => false
    self.table_name_suffix = ""

    ##
    # :singleton-method:
    # Indicates whether table names should be the pluralized versions of the corresponding class names.
    # If true, the default table name for a Product class will be +products+. If false, it would just be +product+.
    # See table_name for the full rules on table/class naming. This is true, by default.
    class_attribute :pluralize_table_names, :instance_writer => false
    self.pluralize_table_names = true

    ##
    # :singleton-method:
    # Determines whether to use Time.local (using :local) or Time.utc (using :utc) when pulling
    # dates and times from the database. This is set to :local by default.
    cattr_accessor :default_timezone, :instance_writer => false
    @@default_timezone = :local

    ##
    # :singleton-method:
    # Specifies the format to use when dumping the database schema with Rails'
    # Rakefile. If :sql, the schema is dumped as (potentially database-
    # specific) SQL statements. If :ruby, the schema is dumped as an
    # ActiveRecord::Schema file which can be loaded into any database that
    # supports migrations. Use :ruby if you want to have different database
    # adapters for, e.g., your development and test environments.
    cattr_accessor :schema_format , :instance_writer => false
    @@schema_format = :ruby

    ##
    # :singleton-method:
    # Specify whether or not to use timestamps for migration versions
    cattr_accessor :timestamped_migrations , :instance_writer => false
    @@timestamped_migrations = true

    # Determine whether to store the full constant name including namespace when using STI
    class_attribute :store_full_sti_class
    self.store_full_sti_class = true

    # Stores the default scope for the class
    class_attribute :default_scopes, :instance_writer => false
    self.default_scopes = []

    # Returns a hash of all the attributes that have been specified for serialization as
    # keys and their class restriction as values.
    class_attribute :serialized_attributes
    self.serialized_attributes = {}

    class_attribute :_attr_readonly, :instance_writer => false
    self._attr_readonly = []

    class << self # Class methods
      delegate :find, :first, :first!, :last, :last!, :all, :exists?, :any?, :many?, :to => :scoped
      delegate :first_or_create, :first_or_create!, :first_or_initialize, :to => :scoped
      delegate :destroy, :destroy_all, :delete, :delete_all, :update, :update_all, :to => :scoped
      delegate :find_each, :find_in_batches, :to => :scoped
      delegate :select, :group, :order, :except, :reorder, :limit, :offset, :joins, :where, :preload, :eager_load, :includes, :from, :lock, :readonly, :having, :create_with, :to => :scoped
      delegate :count, :average, :minimum, :maximum, :sum, :calculate, :to => :scoped

      # Executes a custom SQL query against your database and returns all the results. The results will
      # be returned as an array with columns requested encapsulated as attributes of the model you call
      # this method from. If you call <tt>Product.find_by_sql</tt> then the results will be returned in
      # a Product object with the attributes you specified in the SQL query.
      #
      # If you call a complicated SQL query which spans multiple tables the columns specified by the
      # SELECT will be attributes of the model, whether or not they are columns of the corresponding
      # table.
      #
      # The +sql+ parameter is a full SQL query as a string. It will be called as is, there will be
      # no database agnostic conversions performed. This should be a last resort because using, for example,
      # MySQL specific terms will lock you to using that particular database engine or require you to
      # change your call if you switch engines.
      #
      # ==== Examples
      #   # A simple SQL query spanning multiple tables
      #   Post.find_by_sql "SELECT p.title, c.author FROM posts p, comments c WHERE p.id = c.post_id"
      #   > [#<Post:0x36bff9c @attributes={"title"=>"Ruby Meetup", "first_name"=>"Quentin"}>, ...]
      #
      #   # You can use the same string replacement techniques as you can with ActiveRecord#find
      #   Post.find_by_sql ["SELECT title FROM posts WHERE author = ? AND created > ?", author_id, start_date]
      #   > [#<Post:0x36bff9c @attributes={"title"=>"The Cheap Man Buys Twice"}>, ...]
      def find_by_sql(sql, binds = [])
        connection.select_all(sanitize_sql(sql), "#{name} Load", binds).collect! { |record| instantiate(record) }
      end

      # Creates an object (or multiple objects) and saves it to the database, if validations pass.
      # The resulting object is returned whether the object was saved successfully to the database or not.
      #
      # The +attributes+ parameter can be either be a Hash or an Array of Hashes. These Hashes describe the
      # attributes on the objects that are to be created.
      #
      # +create+ respects mass-assignment security and accepts either +:as+ or +:without_protection+ options
      # in the +options+ parameter.
      #
      # ==== Examples
      #   # Create a single new object
      #   User.create(:first_name => 'Jamie')
      #
      #   # Create a single new object using the :admin mass-assignment security role
      #   User.create({ :first_name => 'Jamie', :is_admin => true }, :as => :admin)
      #
      #   # Create a single new object bypassing mass-assignment security
      #   User.create({ :first_name => 'Jamie', :is_admin => true }, :without_protection => true)
      #
      #   # Create an Array of new objects
      #   User.create([{ :first_name => 'Jamie' }, { :first_name => 'Jeremy' }])
      #
      #   # Create a single object and pass it into a block to set other attributes.
      #   User.create(:first_name => 'Jamie') do |u|
      #     u.is_admin = false
      #   end
      #
      #   # Creating an Array of new objects using a block, where the block is executed for each object:
      #   User.create([{ :first_name => 'Jamie' }, { :first_name => 'Jeremy' }]) do |u|
      #     u.is_admin = false
      #   end
      def create(attributes = nil, options = {}, &block)
        if attributes.is_a?(Array)
          attributes.collect { |attr| create(attr, options, &block) }
        else
          object = new(attributes, options, &block)
          object.save
          object
        end
      end

      # Returns the result of an SQL statement that should only include a COUNT(*) in the SELECT part.
      # The use of this method should be restricted to complicated SQL queries that can't be executed
      # using the ActiveRecord::Calculations class methods. Look into those before using this.
      #
      # ==== Parameters
      #
      # * +sql+ - An SQL statement which should return a count query from the database, see the example below.
      #
      # ==== Examples
      #
      #   Product.count_by_sql "SELECT COUNT(*) FROM sales s, customers c WHERE s.customer_id = c.id"
      def count_by_sql(sql)
        sql = sanitize_conditions(sql)
        connection.select_value(sql, "#{name} Count").to_i
      end

      # Attributes listed as readonly will be used to create a new record but update operations will
      # ignore these fields.
      def attr_readonly(*attributes)
        self._attr_readonly = Set.new(attributes.map { |a| a.to_s }) + (self._attr_readonly || [])
      end

      # Returns an array of all the attributes that have been specified as readonly.
      def readonly_attributes
        self._attr_readonly
      end

      # If you have an attribute that needs to be saved to the database as an object, and retrieved as the same object,
      # then specify the name of that attribute using this method and it will be handled automatically.
      # The serialization is done through YAML. If +class_name+ is specified, the serialized object must be of that
      # class on retrieval or SerializationTypeMismatch will be raised.
      #
      # ==== Parameters
      #
      # * +attr_name+ - The field name that should be serialized.
      # * +class_name+ - Optional, class name that the object type should be equal to.
      #
      # ==== Example
      #   # Serialize a preferences attribute
      #   class User < ActiveRecord::Base
      #     serialize :preferences
      #   end
      def serialize(attr_name, class_name = Object)
        coder = if [:load, :dump].all? { |x| class_name.respond_to?(x) }
                  class_name
                else
                  Coders::YAMLColumn.new(class_name)
                end

        # merge new serialized attribute and create new hash to ensure that each class in inheritance hierarchy
        # has its own hash of own serialized attributes
        self.serialized_attributes = serialized_attributes.merge(attr_name.to_s => coder)
      end

      # Guesses the table name (in forced lower-case) based on the name of the class in the
      # inheritance hierarchy descending directly from ActiveRecord::Base. So if the hierarchy
      # looks like: Reply < Message < ActiveRecord::Base, then Message is used
      # to guess the table name even when called on Reply. The rules used to do the guess
      # are handled by the Inflector class in Active Support, which knows almost all common
      # English inflections. You can add new inflections in config/initializers/inflections.rb.
      #
      # Nested classes are given table names prefixed by the singular form of
      # the parent's table name. Enclosing modules are not considered.
      #
      # ==== Examples
      #
      #   class Invoice < ActiveRecord::Base
      #   end
      #
      #   file                  class               table_name
      #   invoice.rb            Invoice             invoices
      #
      #   class Invoice < ActiveRecord::Base
      #     class Lineitem < ActiveRecord::Base
      #     end
      #   end
      #
      #   file                  class               table_name
      #   invoice.rb            Invoice::Lineitem   invoice_lineitems
      #
      #   module Invoice
      #     class Lineitem < ActiveRecord::Base
      #     end
      #   end
      #
      #   file                  class               table_name
      #   invoice/lineitem.rb   Invoice::Lineitem   lineitems
      #
      # Additionally, the class-level +table_name_prefix+ is prepended and the
      # +table_name_suffix+ is appended. So if you have "myapp_" as a prefix,
      # the table name guess for an Invoice class becomes "myapp_invoices".
      # Invoice::Lineitem becomes "myapp_invoice_lineitems".
      #
      # You can also overwrite this class method to allow for unguessable
      # links, such as a Mouse class with a link to a "mice" table. Example:
      #
      #   class Mouse < ActiveRecord::Base
      #     set_table_name "mice"
      #   end
      def table_name
        reset_table_name
      end

      # Returns a quoted version of the table name, used to construct SQL statements.
      def quoted_table_name
        @quoted_table_name ||= connection.quote_table_name(table_name)
      end

      # Computes the table name, (re)sets it internally, and returns it.
      def reset_table_name #:nodoc:
        return if abstract_class?

        self.table_name = compute_table_name
      end

      def full_table_name_prefix #:nodoc:
        (parents.detect{ |p| p.respond_to?(:table_name_prefix) } || self).table_name_prefix
      end

      # Defines the column name for use with single table inheritance. Use
      # <tt>set_inheritance_column</tt> to set a different value.
      def inheritance_column
        @inheritance_column ||= "type"
      end

      # Lazy-set the sequence name to the connection's default. This method
      # is only ever called once since set_sequence_name overrides it.
      def sequence_name #:nodoc:
        reset_sequence_name
      end

      def reset_sequence_name #:nodoc:
        default = connection.default_sequence_name(table_name, primary_key)
        set_sequence_name(default)
        default
      end

      # Sets the table name. If the value is nil or false then the value returned by the given
      # block is used.
      #
      #   class Project < ActiveRecord::Base
      #     set_table_name "project"
      #   end
      def set_table_name(value = nil, &block)
        @quoted_table_name = nil
        define_attr_method :table_name, value, &block
        @arel_table = nil

        @relation = Relation.new(self, arel_table)
      end
      alias :table_name= :set_table_name

      # Sets the name of the inheritance column to use to the given value,
      # or (if the value # is nil or false) to the value returned by the
      # given block.
      #
      #   class Project < ActiveRecord::Base
      #     set_inheritance_column do
      #       original_inheritance_column + "_id"
      #     end
      #   end
      def set_inheritance_column(value = nil, &block)
        define_attr_method :inheritance_column, value, &block
      end
      alias :inheritance_column= :set_inheritance_column

      # Sets the name of the sequence to use when generating ids to the given
      # value, or (if the value is nil or false) to the value returned by the
      # given block. This is required for Oracle and is useful for any
      # database which relies on sequences for primary key generation.
      #
      # If a sequence name is not explicitly set when using Oracle or Firebird,
      # it will default to the commonly used pattern of: #{table_name}_seq
      #
      # If a sequence name is not explicitly set when using PostgreSQL, it
      # will discover the sequence corresponding to your primary key for you.
      #
      #   class Project < ActiveRecord::Base
      #     set_sequence_name "projectseq"   # default would have been "project_seq"
      #   end
      def set_sequence_name(value = nil, &block)
        define_attr_method :sequence_name, value, &block
      end
      alias :sequence_name= :set_sequence_name

      # Indicates whether the table associated with this class exists
      def table_exists?
        connection.table_exists?(table_name)
      end

      # Returns an array of column objects for the table associated with this class.
      def columns
        connection_pool.columns[table_name]
      end

      # Returns a hash of column objects for the table associated with this class.
      def columns_hash
        connection_pool.columns_hash[table_name]
      end

      # Returns a hash where the keys are column names and the values are
      # default values when instantiating the AR object for this table.
      def column_defaults
        connection_pool.column_defaults[table_name]
      end

      # Returns an array of column names as strings.
      def column_names
        @column_names ||= columns.map { |column| column.name }
      end

      # Returns an array of column objects where the primary id, all columns ending in "_id" or "_count",
      # and columns used for single table inheritance have been removed.
      def content_columns
        @content_columns ||= columns.reject { |c| c.primary || c.name =~ /(_id|_count)$/ || c.name == inheritance_column }
      end

      # Returns a hash of all the methods added to query each of the columns in the table with the name of the method as the key
      # and true as the value. This makes it possible to do O(1) lookups in respond_to? to check if a given method for attribute
      # is available.
      def column_methods_hash #:nodoc:
        @dynamic_methods_hash ||= column_names.inject(Hash.new(false)) do |methods, attr|
          attr_name = attr.to_s
          methods[attr.to_sym]       = attr_name
          methods["#{attr}=".to_sym] = attr_name
          methods["#{attr}?".to_sym] = attr_name
          methods["#{attr}_before_type_cast".to_sym] = attr_name
          methods
        end
      end

      # Resets all the cached information about columns, which will cause them
      # to be reloaded on the next request.
      #
      # The most common usage pattern for this method is probably in a migration,
      # when just after creating a table you want to populate it with some default
      # values, eg:
      #
      #  class CreateJobLevels < ActiveRecord::Migration
      #    def self.up
      #      create_table :job_levels do |t|
      #        t.integer :id
      #        t.string :name
      #
      #        t.timestamps
      #      end
      #
      #      JobLevel.reset_column_information
      #      %w{assistant executive manager director}.each do |type|
      #        JobLevel.create(:name => type)
      #      end
      #    end
      #
      #    def self.down
      #      drop_table :job_levels
      #    end
      #  end
      def reset_column_information
        connection.clear_cache!
        undefine_attribute_methods
        connection_pool.clear_table_cache!(table_name) if table_exists?

        @column_names = @content_columns = @dynamic_methods_hash = @inheritance_column = nil
        @arel_engine = @relation = nil
      end

      def clear_cache! # :nodoc:
        connection_pool.clear_cache!
      end

      def attribute_method?(attribute)
        super || (table_exists? && column_names.include?(attribute.to_s.sub(/=$/, '')))
      end

      # Returns an array of column names as strings if it's not
      # an abstract class and table exists.
      # Otherwise it returns an empty array.
      def attribute_names
        @attribute_names ||= if !abstract_class? && table_exists?
            column_names
          else
            []
          end
      end

      # Set the lookup ancestors for ActiveModel.
      def lookup_ancestors #:nodoc:
        klass = self
        classes = [klass]
        return classes if klass == ActiveRecord::Base

        while klass != klass.base_class
          classes << klass = klass.superclass
        end
        classes
      end

      # Set the i18n scope to overwrite ActiveModel.
      def i18n_scope #:nodoc:
        :activerecord
      end

      # True if this isn't a concrete subclass needing a STI type condition.
      def descends_from_active_record?
        if superclass.abstract_class?
          superclass.descends_from_active_record?
        else
          superclass == Base || !columns_hash.include?(inheritance_column)
        end
      end

      def finder_needs_type_condition? #:nodoc:
        # This is like this because benchmarking justifies the strange :false stuff
        :true == (@finder_needs_type_condition ||= descends_from_active_record? ? :false : :true)
      end

      # Returns a string like 'Post(id:integer, title:string, body:text)'
      def inspect
        if self == Base
          super
        elsif abstract_class?
          "#{super}(abstract)"
        elsif table_exists?
          attr_list = columns.map { |c| "#{c.name}: #{c.type}" } * ', '
          "#{super}(#{attr_list})"
        else
          "#{super}(Table doesn't exist)"
        end
      end

      def quote_value(value, column = nil) #:nodoc:
        connection.quote(value,column)
      end

      # Used to sanitize objects before they're used in an SQL SELECT statement. Delegates to <tt>connection.quote</tt>.
      def sanitize(object) #:nodoc:
        connection.quote(object)
      end

      # Overwrite the default class equality method to provide support for association proxies.
      def ===(object)
        object.is_a?(self)
      end

      def symbolized_base_class
        @symbolized_base_class ||= base_class.to_s.to_sym
      end

      def symbolized_sti_name
        @symbolized_sti_name ||= sti_name.present? ? sti_name.to_sym : symbolized_base_class
      end

      # Returns the base AR subclass that this class descends from. If A
      # extends AR::Base, A.base_class will return A. If B descends from A
      # through some arbitrarily deep hierarchy, B.base_class will return A.
      #
      # If B < A and C < B and if A is an abstract_class then both B.base_class
      # and C.base_class would return B as the answer since A is an abstract_class.
      def base_class
        class_of_active_record_descendant(self)
      end

      # Set this to true if this is an abstract class (see <tt>abstract_class?</tt>).
      attr_accessor :abstract_class

      # Returns whether this class is an abstract class or not.
      def abstract_class?
        defined?(@abstract_class) && @abstract_class == true
      end

      def respond_to?(method_id, include_private = false)
        if match = DynamicFinderMatch.match(method_id)
          return true if all_attributes_exists?(match.attribute_names)
        elsif match = DynamicScopeMatch.match(method_id)
          return true if all_attributes_exists?(match.attribute_names)
        end

        super
      end

      def sti_name
        store_full_sti_class ? name : name.demodulize
      end

      def arel_table
        @arel_table ||= Arel::Table.new(table_name, arel_engine)
      end

      def arel_engine
        @arel_engine ||= begin
          if self == ActiveRecord::Base
            ActiveRecord::Base
          else
            connection_handler.connection_pools[name] ? self : superclass.arel_engine
          end
        end
      end

      # Returns a scope for this class without taking into account the default_scope.
      #
      #   class Post < ActiveRecord::Base
      #     def self.default_scope
      #       where :published => true
      #     end
      #   end
      #
      #   Post.all          # Fires "SELECT * FROM posts WHERE published = true"
      #   Post.unscoped.all # Fires "SELECT * FROM posts"
      #
      # This method also accepts a block meaning that all queries inside the block will
      # not use the default_scope:
      #
      #   Post.unscoped {
      #     Post.limit(10) # Fires "SELECT * FROM posts LIMIT 10"
      #   }
      #
      # It is recommended to use block form of unscoped because chaining unscoped with <tt>scope</tt>
      # does not work. Assuming that <tt>published</tt> is a <tt>scope</tt> following two statements are same.
      #
      # Post.unscoped.published
      # Post.published
      def unscoped #:nodoc:
        block_given? ? relation.scoping { yield } : relation
      end

      def before_remove_const #:nodoc:
        self.current_scope = nil
      end

      # Finder methods must instantiate through this method to work with the
      # single-table inheritance model that makes it possible to create
      # objects of different types from the same table.
      def instantiate(record)
        sti_class = find_sti_class(record[inheritance_column])
        record_id = sti_class.primary_key && record[sti_class.primary_key]

        if ActiveRecord::IdentityMap.enabled? && record_id
          if (column = sti_class.columns_hash[sti_class.primary_key]) && column.number?
            record_id = record_id.to_i
          end
          if instance = IdentityMap.get(sti_class, record_id)
            instance.reinit_with('attributes' => record)
          else
            instance = sti_class.allocate.init_with('attributes' => record)
            IdentityMap.add(instance)
          end
        else
          instance = sti_class.allocate.init_with('attributes' => record)
        end

        instance
      end

      private

        def relation #:nodoc:
          @relation ||= Relation.new(self, arel_table)

          if finder_needs_type_condition?
            @relation.where(type_condition).create_with(inheritance_column.to_sym => sti_name)
          else
            @relation
          end
        end

        def find_sti_class(type_name)
          if type_name.blank? || !columns_hash.include?(inheritance_column)
            self
          else
            begin
              if store_full_sti_class
                ActiveSupport::Dependencies.constantize(type_name)
              else
                compute_type(type_name)
              end
            rescue NameError
              raise SubclassNotFound,
                "The single-table inheritance mechanism failed to locate the subclass: '#{type_name}'. " +
                "This error is raised because the column '#{inheritance_column}' is reserved for storing the class in case of inheritance. " +
                "Please rename this column if you didn't intend it to be used for storing the inheritance class " +
                "or overwrite #{name}.inheritance_column to use another column for that information."
            end
          end
        end

        def construct_finder_arel(options = {}, scope = nil)
          relation = options.is_a?(Hash) ? unscoped.apply_finder_options(options) : options
          relation = scope.merge(relation) if scope
          relation
        end

        def type_condition(table = arel_table)
          sti_column = table[inheritance_column.to_sym]
          sti_names  = ([self] + descendants).map { |model| model.sti_name }

          sti_column.in(sti_names)
        end

        # Guesses the table name, but does not decorate it with prefix and suffix information.
        def undecorated_table_name(class_name = base_class.name)
          table_name = class_name.to_s.demodulize.underscore
          table_name = table_name.pluralize if pluralize_table_names
          table_name
        end

        # Computes and returns a table name according to default conventions.
        def compute_table_name
          base = base_class
          if self == base
            # Nested classes are prefixed with singular parent table name.
            if parent < ActiveRecord::Base && !parent.abstract_class?
              contained = parent.table_name
              contained = contained.singularize if parent.pluralize_table_names
              contained += '_'
            end
            "#{full_table_name_prefix}#{contained}#{undecorated_table_name(name)}#{table_name_suffix}"
          else
            # STI subclasses always use their superclass' table.
            base.table_name
          end
        end

        # Enables dynamic finders like <tt>User.find_by_user_name(user_name)</tt> and
        # <tt>User.scoped_by_user_name(user_name). Refer to Dynamic attribute-based finders
        # section at the top of this file for more detailed information.
        #
        # It's even possible to use all the additional parameters to +find+. For example, the
        # full interface for +find_all_by_amount+ is actually <tt>find_all_by_amount(amount, options)</tt>.
        #
        # Each dynamic finder using <tt>scoped_by_*</tt> is also defined in the class after it
        # is first invoked, so that future attempts to use it do not run through method_missing.
        def method_missing(method_id, *arguments, &block)
          if match = (DynamicFinderMatch.match(method_id) || DynamicScopeMatch.match(method_id))
            attribute_names = match.attribute_names
            super unless all_attributes_exists?(attribute_names)
            if arguments.size < attribute_names.size
              method_trace = "#{__FILE__}:#{__LINE__}:in `#{method_id}'"
              backtrace = [method_trace] + caller
              raise ArgumentError, "wrong number of arguments (#{arguments.size} for #{attribute_names.size})", backtrace
            end
            if match.respond_to?(:scope?) && match.scope?
              self.class_eval <<-METHOD, __FILE__, __LINE__ + 1
                def self.#{method_id}(*args)                                    # def self.scoped_by_user_name_and_password(*args)
                  attributes = Hash[[:#{attribute_names.join(',:')}].zip(args)] #   attributes = Hash[[:user_name, :password].zip(args)]
                                                                                #
                  scoped(:conditions => attributes)                             #   scoped(:conditions => attributes)
                end                                                             # end
              METHOD
              send(method_id, *arguments)
            elsif match.finder?
              options = arguments.extract_options!
              relation = options.any? ? scoped(options) : scoped
              relation.send :find_by_attributes, match, attribute_names, *arguments, &block
            elsif match.instantiator?
              scoped.send :find_or_instantiator_by_attributes, match, attribute_names, *arguments, &block
            end
          else
            super
          end
        end

        # Similar in purpose to +expand_hash_conditions_for_aggregates+.
        def expand_attribute_names_for_aggregates(attribute_names)
          attribute_names.map { |attribute_name|
            unless (aggregation = reflect_on_aggregation(attribute_name.to_sym)).nil?
              aggregate_mapping(aggregation).map do |field_attr, _|
                field_attr.to_sym
              end
            else
              attribute_name.to_sym
            end
          }.flatten
        end

        def all_attributes_exists?(attribute_names)
          (expand_attribute_names_for_aggregates(attribute_names) -
           column_methods_hash.keys).empty?
        end

      protected
        # with_scope lets you apply options to inner block incrementally. It takes a hash and the keys must be
        # <tt>:find</tt> or <tt>:create</tt>. <tt>:find</tt> parameter is <tt>Relation</tt> while
        # <tt>:create</tt> parameters are an attributes hash.
        #
        #   class Article < ActiveRecord::Base
        #     def self.create_with_scope
        #       with_scope(:find => where(:blog_id => 1), :create => { :blog_id => 1 }) do
        #         find(1) # => SELECT * from articles WHERE blog_id = 1 AND id = 1
        #         a = create(1)
        #         a.blog_id # => 1
        #       end
        #     end
        #   end
        #
        # In nested scopings, all previous parameters are overwritten by the innermost rule, with the exception of
        # <tt>where</tt>, <tt>includes</tt>, and <tt>joins</tt> operations in <tt>Relation</tt>, which are merged.
        #
        # <tt>joins</tt> operations are uniqued so multiple scopes can join in the same table without table aliasing
        # problems. If you need to join multiple tables, but still want one of the tables to be uniqued, use the
        # array of strings format for your joins.
        #
        #   class Article < ActiveRecord::Base
        #     def self.find_with_scope
        #       with_scope(:find => where(:blog_id => 1).limit(1), :create => { :blog_id => 1 }) do
        #         with_scope(:find => limit(10)) do
        #           all # => SELECT * from articles WHERE blog_id = 1 LIMIT 10
        #         end
        #         with_scope(:find => where(:author_id => 3)) do
        #           all # => SELECT * from articles WHERE blog_id = 1 AND author_id = 3 LIMIT 1
        #         end
        #       end
        #     end
        #   end
        #
        # You can ignore any previous scopings by using the <tt>with_exclusive_scope</tt> method.
        #
        #   class Article < ActiveRecord::Base
        #     def sel