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 ::establish_connection
and retrieved by #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
-
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 inestablish_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. Somefind
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. Theerrors
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 theattribute
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.
- #
- A
- C
- D
- E
- F
- G
- H
- I
- L
- M
- N
- R
- S
- T
- ActiveRecord::Persistence
- ActiveRecord::ReadonlyAttributes
- ActiveRecord::ModelSchema
- ActiveRecord::Inheritance
- ActiveRecord::Scoping
- ActiveRecord::Sanitization
- ActiveRecord::AttributeAssignment
- ActiveModel::Conversion
- ActiveRecord::Integration
- ActiveRecord::Validations
- ActiveRecord::Locking::Optimistic
- ActiveRecord::Locking::Pessimistic
- ActiveRecord::AttributeMethods
- ActiveRecord::Callbacks
- ActiveModel::Observing
- ActiveRecord::Timestamp
- ActiveRecord::Associations
- ActiveRecord::IdentityMap
- ActiveModel::SecurePassword
- ActiveRecord::AutosaveAssociation
- ActiveRecord::NestedAttributes
- ActiveRecord::Aggregations
- ActiveRecord::Transactions
- ActiveRecord::Reflection
- ActiveRecord::AttributeMethods::Serialization
- ActiveRecord::Store
Overwrite the default class equality method to provide support for association proxies.
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 ::configurations to look like this:
{ 'development' => { 'adapter' => 'sqlite3', 'database' => 'db/development.sqlite3' }, 'production' => { 'adapter' => 'sqlite3', 'database' => 'db/production.sqlite3' } }
Returns true if Active Record is connected.
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.
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.
The connection handler
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.
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 activerecord/lib/active_record/connection_adapters/abstract/connection_specification.rb, line 128 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
Returns a string like 'Post(id:integer, title:string, body:text)'
# File activerecord/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
.
Establishes a connection to the database that's used by all Active Record objects.
# File activerecord/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.
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 activerecord/lib/active_record/base.rb, line 481 def initialize(attributes = nil, options = {}) defaults = Hash[self.class.column_defaults.map { |k, v| [k, v.duplicable? ? v.dup : v] }] @attributes = self.class.initialize_attributes(defaults) @association_cache = {} @aggregation_cache = {} @attributes_cache = {} @new_record = true @readonly = false @destroyed = false @marked_for_destruction = false @previously_changed = {} @changed_attributes = {} ensure_proper_type populate_with_current_scope_attributes assign_attributes(attributes, options) if attributes yield self if block_given? run_callbacks :initialize 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.
Specify whether or not to use timestamps for migration versions
Allows sort on objects
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.
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.
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, ... }
Freeze the attributes hash such that associations are still accessible, even on destroyed records.
Returns true
if the attributes hash has been frozen.
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) ]
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 activerecord/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 activerecord/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 super end
Returns the contents of the record as a nicely formatted string.
# File activerecord/lib/active_record/base.rb, line 638 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
Marks this record as read only.