Object
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.
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 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' )
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).
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
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 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')
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"
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
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.
ActiveRecordError - Generic error class and superclass of all other errors raised by Active Record.
AdapterNotSpecified - The configuration hash used in establish_connection didn't include an :adapter key.
AdapterNotFound - The :adapter key used in establish_connection 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 establish_connection 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 attributes= 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 attributes= 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 Base.logger= which will then be used by all instances in the current object space.
Overwrite the default class equality method to provide support for association proxies.
# File lib/active_record/base.rb, line 432 def ===(object) object.is_a?(self) end
# File lib/active_record/base.rb, line 440 def arel_engine @arel_engine ||= begin if self == ActiveRecord::Base ActiveRecord::Base else connection_handler.retrieve_connection_pool(self) ? self : superclass.arel_engine end end end
# File lib/active_record/base.rb, line 436 def arel_table @arel_table ||= Arel::Table.new(table_name, arel_engine) end
# File lib/active_record/connection_adapters/abstract/connection_specification.rb, line 182 def clear_active_connections! connection_handler.clear_active_connections! end
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 cattr_accessor :configurations, :instance_writer => false
Returns true if Active Record is connected.
# File lib/active_record/connection_adapters/abstract/connection_specification.rb, line 174 def connected? connection_handler.connected?(self) end
Returns the connection currently associated with the class. This can also be used to "borrow" the connection to do database work unrelated to any of the specific Active Records.
# File lib/active_record/connection_adapters/abstract/connection_specification.rb, line 143 def connection retrieve_connection end
Returns the configuration of the associated connection as a hash:
ActiveRecord::Base.connection_config # => {:pool=>5, :timeout=>5000, :database=>"db/development.sqlite3", :adapter=>"sqlite3"}
Please use only for reading.
# File lib/active_record/connection_adapters/abstract/connection_specification.rb, line 161 def connection_config connection_pool.spec.config end
The connection handler
# File lib/active_record/connection_adapters/abstract/connection_specification.rb, line 83 class_attribute :connection_handler, :instance_writer => false
# File lib/active_record/connection_adapters/abstract/connection_specification.rb, line 147 def connection_id Thread.current['ActiveRecord::Base.connection_id'] end
# File lib/active_record/connection_adapters/abstract/connection_specification.rb, line 151 def connection_id=(connection_id) Thread.current['ActiveRecord::Base.connection_id'] = connection_id end
# File lib/active_record/connection_adapters/abstract/connection_specification.rb, line 165 def connection_pool connection_handler.retrieve_connection_pool(self) or raise ConnectionNotEstablished end
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 cattr_accessor :default_timezone, :instance_writer => false
Establishes the connection to the database. Accepts a hash as input where the :adapter key must be specified with the name of a database adapter (in lower-case) example for regular databases (MySQL, Postgresql, etc):
ActiveRecord::Base.establish_connection( :adapter => "mysql", :host => "localhost", :username => "myuser", :password => "mypass", :database => "somedatabase" )
Example for SQLite database:
ActiveRecord::Base.establish_connection( :adapter => "sqlite", :database => "path/to/dbfile" )
Also accepts keys as strings (for parsing from YAML for example):
ActiveRecord::Base.establish_connection( "adapter" => "sqlite", "database" => "path/to/dbfile" )
Or a URL:
ActiveRecord::Base.establish_connection( "postgres://myuser:mypass@localhost/somedatabase" )
The exceptions AdapterNotSpecified, AdapterNotFound and ArgumentError may be returned on an error.
# File lib/active_record/connection_adapters/abstract/connection_specification.rb, line 127 def self.establish_connection(spec = ENV["DATABASE_URL"]) resolver = ConnectionSpecification::Resolver.new spec, configurations spec = resolver.spec unless respond_to?(spec.adapter_method) raise AdapterNotFound, "database configuration specifies nonexistent #{spec.config[:adapter]} adapter" end remove_connection connection_handler.establish_connection name, spec end
# File lib/active_record/base.rb, line 409 def generated_feature_methods @generated_feature_methods ||= begin mod = const_set(:GeneratedFeatureMethods, Module.new) include mod mod end end
Returns a string like 'Post(id:integer, title:string, body:text)'
# File lib/active_record/base.rb, line 418 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
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 cattr_accessor :logger, :instance_writer => false
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 def self.mysql2_connection(config) config[:username] = 'root' if config[:username].nil? if Mysql2::Client.const_defined? :FOUND_ROWS config[:flags] = Mysql2::Client::FOUND_ROWS end client = Mysql2::Client.new(config.symbolize_keys) options = [config[:host], config[:username], config[:password], config[:database], config[:port], config[:socket], 0] ConnectionAdapters::Mysql2Adapter.new(client, logger, options, config) end
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.
# 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 def initialize(attributes = nil, options = {}) @attributes = self.class.initialize_attributes(self.class.column_defaults.dup) @association_cache = {} @aggregation_cache = {} @attributes_cache = {} @new_record = true @readonly = false @destroyed = false @marked_for_destruction = false @previously_changed = {} @changed_attributes = {} @relation = nil ensure_proper_type populate_with_current_scope_attributes assign_attributes(attributes, options) if attributes yield self if block_given? run_callbacks :initialize end
# File lib/active_record/connection_adapters/abstract/connection_specification.rb, line 178 def remove_connection(klass = self) connection_handler.remove_connection(klass) end
# File lib/active_record/connection_adapters/abstract/connection_specification.rb, line 169 def retrieve_connection connection_handler.retrieve_connection(self) end
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 cattr_accessor :schema_format , :instance_writer => false
Allows sort on objects
# File lib/active_record/base.rb, line 619 def <=>(other_object) if other_object.is_a?(self.class) self.to_key <=> other_object.to_key else nil end end
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 def ==(comparison_object) super || comparison_object.instance_of?(self.class) && id.present? && comparison_object.id == id end
Returns the connection currently associated with the class. This can also be used to "borrow" the connection to do database work that isn't easily done without going straight to SQL.
# File lib/active_record/connection_adapters/abstract/connection_specification.rb, line 89 def connection self.class.connection end
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 def encode_with(coder) coder['attributes'] = attributes end
Freeze the attributes hash such that associations are still accessible, even on destroyed records.
# File lib/active_record/base.rb, line 609 def freeze @attributes.freeze; self end
Returns true if the attributes hash has been frozen.
# File lib/active_record/base.rb, line 614 def frozen? @attributes.frozen? end
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 def hash id.hash end
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 def init_with(coder) @attributes = self.class.initialize_attributes(coder['attributes']) @relation = nil @attributes_cache, @previously_changed, @changed_attributes = {}, {}, {} @association_cache = {} @aggregation_cache = {} @readonly = @destroyed = @marked_for_destruction = false @new_record = false run_callbacks :find run_callbacks :initialize self end
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 def initialize_dup(other) cloned_attributes = other.clone_attributes(:read_attribute_before_type_cast) self.class.initialize_attributes(cloned_attributes, :serialized => false) cloned_attributes.delete(self.class.primary_key) @attributes = cloned_attributes _run_after_initialize_callbacks if respond_to?(:_run_after_initialize_callbacks) @changed_attributes = {} self.class.column_defaults.each do |attr, orig_value| @changed_attributes[attr] = orig_value if field_changed?(attr, orig_value, @attributes[attr]) end @aggregation_cache = {} @association_cache = {} @attributes_cache = {} @new_record = true ensure_proper_type populate_with_current_scope_attributes super end
Returns the contents of the record as a nicely formatted string.
# File lib/active_record/base.rb, line 639 def inspect inspection = if @attributes self.class.column_names.collect { |name| if has_attribute?(name) "#{name}: #{attribute_for_inspect(name)}" end }.compact.join(", ") else "not initialized" end "#<#{self.class} #{inspection}>" end
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