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ActiveRecord::Base

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 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 authenticate_unsafely method inserts the parameters directly into the query and is thus susceptible to SQL-injection attacks if the user_name and password parameters come directly from an HTTP request. The authenticate_safely and authenticate_safely_simply both will sanitize the user_name 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 => { :category => 'public' })
  Student.joins(:schools).where('schools.category' => '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 read_attribute(attr_name) and write_attribute(attr_name, value) 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 self[:attribute]=(value) and self[:attribute] instead of write_attribute(:attribute, value) and read_attribute(:attribute).

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 name attribute has a name? 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 <attribute>_before_type_cast accessors that all attributes have. For example, if your Account model has a balance attribute, you can call account.balance_before_type_cast or account.id_before_type_cast.

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 find_by_, find_last_by_, or find_all_by_ and thus produces finders like Person.find_by_user_name, Person.find_all_by_last_name, and Payment.find_by_transaction_id. Instead of writing Person.where(:user_name => user_name).first, you just do Person.find_by_user_name(user_name). And instead of writing Person.where(:last_name => last_name).all, you just do Person.find_all_by_last_name(last_name).

It’s possible to add an exclamation point (!) on the end of the dynamic finders to get them to raise an ActiveRecord::RecordNotFound error if they do not return any records, like Person.find_by_last_name!.

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 find_or_create_by_ 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 }

Adding an exclamation point (!) on to the end of find_or_create_by_ will raise an ActiveRecord::RecordInvalid error if the new record is invalid.

Use the find_or_initialize_by_ 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 find_by_*, you can also use scoped_by_* to retrieve data. The good thing about using this feature is that the very first time result is returned using method_missing technique but after that the method is declared on the class. Henceforth method_missing 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 Base.inheritance_column). 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 Firm.create(:name => "37signals"), this record will be saved in the companies table with type = “Firm”. You can then fetch this row again using Company.where(:name => '37signals').first 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: 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 Course.establish_connection 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

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 Base.logger= which will then be used by all instances in the current object space.

Public Class Methods

===(object) click to toggle source

Overwrite the default class equality method to provide support for association proxies.

     # File lib/active_record/base.rb, line 432
432:       def ===(object)
433:         object.is_a?(self)
434:       end
arel_engine() click to toggle source
     # File lib/active_record/base.rb, line 440
440:       def arel_engine
441:         @arel_engine ||= begin
442:           if self == ActiveRecord::Base
443:             ActiveRecord::Base
444:           else
445:             connection_handler.retrieve_connection_pool(self) ? self : superclass.arel_engine
446:           end
447:         end
448:       end
arel_table() click to toggle source
     # File lib/active_record/base.rb, line 436
436:       def arel_table
437:         @arel_table ||= Arel::Table.new(table_name, arel_engine)
438:       end
configurations click to toggle source

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'
     }
  }
     # File lib/active_record/base.rb, line 368
368:     cattr_accessor :configurations, :instance_writer => false
default_timezone click to toggle source

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.

     # File lib/active_record/base.rb, line 375
375:     cattr_accessor :default_timezone, :instance_writer => false
generated_feature_methods() click to toggle source
     # File lib/active_record/base.rb, line 409
409:       def generated_feature_methods
410:         @generated_feature_methods ||= begin
411:           mod = const_set(:GeneratedFeatureMethods, Module.new)
412:           include mod
413:           mod
414:         end
415:       end
inspect() click to toggle source

Returns a string like ‘Post(id:integer, title:string, body:text)’

     # File lib/active_record/base.rb, line 418
418:       def inspect
419:         if self == Base
420:           super
421:         elsif abstract_class?
422:           "#{super}(abstract)"
423:         elsif table_exists?
424:           attr_list = columns.map { |c| "#{c.name}: #{c.type}" } * ', '
425:           "#{super}(#{attr_list})"
426:         else
427:           "#{super}(Table doesn't exist)"
428:         end
429:       end
logger click to toggle source

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.

     # File lib/active_record/base.rb, line 339
339:     cattr_accessor :logger, :instance_writer => false
mysql2_connection(config) click to toggle source

Establishes a connection to the database that’s used by all Active Record objects.

    # File lib/active_record/connection_adapters/mysql2_adapter.rb, line 9
 9:     def self.mysql2_connection(config)
10:       config[:username] = 'root' if config[:username].nil?
11: 
12:       if Mysql2::Client.const_defined? :FOUND_ROWS
13:         config[:flags] = Mysql2::Client::FOUND_ROWS
14:       end
15: 
16:       client = Mysql2::Client.new(config.symbolize_keys)
17:       options = [config[:host], config[:username], config[:password], config[:database], config[:port], config[:socket], 0]
18:       ConnectionAdapters::Mysql2Adapter.new(client, logger, options, config)
19:     end
new(attributes = nil, options = {}) click to toggle source

New objects can be instantiated as either empty (pass no construction parameter) or pre-set with attributes but not yet saved (pass a hash with key names matching the associated table column names). In both instances, valid attribute keys are determined by the column names of the associated table — hence you can’t have attributes that aren’t part of the table columns.

initialize respects mass-assignment security and accepts either :as or :without_protection options in the options parameter.

Examples

  # Instantiates a single new object
  User.new(:first_name => 'Jamie')

  # Instantiates a single new object using the :admin mass-assignment security role
  User.new({ :first_name => 'Jamie', :is_admin => true }, :as => :admin)

  # Instantiates a single new object bypassing mass-assignment security
  User.new({ :first_name => 'Jamie', :is_admin => true }, :without_protection => true)
     # File lib/active_record/base.rb, line 481
481:       def initialize(attributes = nil, options = {})
482:         @attributes = self.class.initialize_attributes(self.class.column_defaults.dup)
483:         @association_cache = {}
484:         @aggregation_cache = {}
485:         @attributes_cache = {}
486:         @new_record = true
487:         @readonly = false
488:         @destroyed = false
489:         @marked_for_destruction = false
490:         @previously_changed = {}
491:         @changed_attributes = {}
492:         @relation = nil
493: 
494:         ensure_proper_type
495: 
496:         populate_with_current_scope_attributes
497: 
498:         assign_attributes(attributes, options) if attributes
499: 
500:         yield self if block_given?
501:         run_callbacks :initialize
502:       end
schema_format click to toggle source

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.

     # File lib/active_record/base.rb, line 386
386:     cattr_accessor :schema_format , :instance_writer => false
timestamped_migrations click to toggle source

Specify whether or not to use timestamps for migration versions

     # File lib/active_record/base.rb, line 392
392:     cattr_accessor :timestamped_migrations , :instance_writer => false

Public Instance Methods

<=>(other_object) click to toggle source

Allows sort on objects

     # File lib/active_record/base.rb, line 619
619:       def <=>(other_object)
620:         if other_object.is_a?(self.class)
621:           self.to_key <=> other_object.to_key
622:         else
623:           nil
624:         end
625:       end
==(comparison_object) click to toggle source

Returns true if comparison_object is the same exact object, or comparison_object is of the same type and self has an ID and it is equal to comparison_object.id.

Note that new records are different from any other record by definition, unless the other record is the receiver itself. Besides, if you fetch existing records with select and leave the ID out, you’re on your own, this predicate will return false.

Note also that destroying a record preserves its ID in the model instance, so deleted models are still comparable.

     # File lib/active_record/base.rb, line 594
594:       def ==(comparison_object)
595:         super ||
596:           comparison_object.instance_of?(self.class) &&
597:           id.present? &&
598:           comparison_object.id == id
599:       end
Also aliased as: eql?
encode_with(coder) click to toggle source

Populate coder with attributes about this record that should be serialized. The structure of coder defined in this method is guaranteed to match the structure of coder passed to the init_with method.

Example:

  class Post < ActiveRecord::Base
  end
  coder = {}
  Post.new.encode_with(coder)
  coder # => { 'id' => nil, ... }
     # File lib/active_record/base.rb, line 581
581:       def encode_with(coder)
582:         coder['attributes'] = attributes
583:       end
eql?(comparison_object) click to toggle source
Alias for: ==
freeze() click to toggle source

Freeze the attributes hash such that associations are still accessible, even on destroyed records.

     # File lib/active_record/base.rb, line 609
609:       def freeze
610:         @attributes.freeze; self
611:       end
frozen?() click to toggle source

Returns true if the attributes hash has been frozen.

     # File lib/active_record/base.rb, line 614
614:       def frozen?
615:         @attributes.frozen?
616:       end
hash() click to toggle source

Delegates to id in order to allow two records of the same type and id to work with something like:

  [ Person.find(1), Person.find(2), Person.find(3) ] & [ Person.find(1), Person.find(4) ] # => [ Person.find(1) ]
     # File lib/active_record/base.rb, line 604
604:       def hash
605:         id.hash
606:       end
init_with(coder) click to toggle source

Initialize an empty model object from coder. coder must contain the attributes necessary for initializing an empty model object. For example:

  class Post < ActiveRecord::Base
  end

  post = Post.allocate
  post.init_with('attributes' => { 'title' => 'hello world' })
  post.title # => 'hello world'
     # File lib/active_record/base.rb, line 514
514:       def init_with(coder)
515:         @attributes = self.class.initialize_attributes(coder['attributes'])
516:         @relation = nil
517: 
518:         @attributes_cache, @previously_changed, @changed_attributes = {}, {}, {}
519:         @association_cache = {}
520:         @aggregation_cache = {}
521:         @readonly = @destroyed = @marked_for_destruction = false
522:         @new_record = false
523:         run_callbacks :find
524:         run_callbacks :initialize
525: 
526:         self
527:       end
initialize_dup(other) click to toggle source

Duped objects have no id assigned and are treated as new records. Note that this is a “shallow” copy as it copies the object’s attributes only, not its associations. The extent of a “deep” copy is application specific and is therefore left to the application to implement according to its need. The dup method does not preserve the timestamps (created|updated)_(at|on).

     # File lib/active_record/base.rb, line 535
535:       def initialize_dup(other)
536:         cloned_attributes = other.clone_attributes(:read_attribute_before_type_cast)
537:         self.class.initialize_attributes(cloned_attributes, :serialized => false)
538: 
539:         cloned_attributes.delete(self.class.primary_key)
540: 
541:         @attributes = cloned_attributes
542: 
543:         _run_after_initialize_callbacks if respond_to?(:_run_after_initialize_callbacks)
544: 
545:         @changed_attributes = {}
546:         self.class.column_defaults.each do |attr, orig_value|
547:           @changed_attributes[attr] = orig_value if field_changed?(attr, orig_value, @attributes[attr])
548:         end
549: 
550:         @aggregation_cache = {}
551:         @association_cache = {}
552:         @attributes_cache = {}
553:         @new_record  = true
554: 
555:         ensure_proper_type
556:         populate_with_current_scope_attributes
557:         super
558:       end
inspect() click to toggle source

Returns the contents of the record as a nicely formatted string.

     # File lib/active_record/base.rb, line 639
639:       def inspect
640:         inspection = if @attributes
641:                        self.class.column_names.collect { |name|
642:                          if has_attribute?(name)
643:                            "#{name}: #{attribute_for_inspect(name)}"
644:                          end
645:                        }.compact.join(", ")
646:                      else
647:                        "not initialized"
648:                      end
649:         "#<#{self.class} #{inspection}>"
650:       end
readonly!() click to toggle source

Marks this record as read only.

     # File lib/active_record/base.rb, line 634
634:       def readonly!
635:         @readonly = true
636:       end
readonly?() click to toggle source

Returns true if the record is read only. Records loaded through joins with piggy-back attributes will be marked as read only since they cannot be saved.

     # File lib/active_record/base.rb, line 629
629:       def readonly?
630:         @readonly
631:       end

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