Class: ActiveRecord::Base

Active Record objects doesn’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/README.html for more insight.

Creation

Active Records accepts 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 a 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 or an array 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 doesn’t involve tainted data. Examples:

  User < ActiveRecord::Base
    def authenticate_unsafely(user_name, password)
      find_first("user_name = '#{user_name}' AND password = '#{password}'")
    end

    def authenticate_safely(user_name, password)
      find_first([ "user_name = '%s' AND password = '%s'", user_name, password ])
    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 a HTTP request. The authenticate_safely method, on the other hand, 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).

Overwriting default accessors

All column values are automatically available through basic accessors on the Active Record object, but some times you want to specialize this behavior. This can be done by either by overwriting the default accessors (using the same name as the attribute) calling read_attribute(attr_name) and write_attribute(attr_name, value) to actually change things. Example:

  class Song < ActiveRecord::Base
    # Uses an integer of seconds to hold the length of the song

    def length=(minutes)
      write_attribute("length", minutes * 60)
    end

    def length
      read_attribute("length") / 60
    end
  end

Saving arrays, hashes, and other non-mappeable objects in text columns

Active Record will automatically attempt to serialize (using YAML) any object in text columns that isn’t either a String, NilClass, TrueClass, FalseClass, Fixnum, Date, or Time. This makes it possible to store arrays, hashes, and other non-mappeable objects without doing any additional work. Example:

   user = User.find(1)
   user.preferences = { "background" => "black", "display" => large }
   user.save

   User.find(1).preferences # => { "background" => "black", "display" => large }

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 a :adapter key.
AdapterNotSpecified — the :adapter key used in establish_connection specified an unexisting adapter (or a bad spelling of an existing one). :adapter key.
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.
StatementInvalid — the database server rejected the SQL statement. The precise error is added in the message. Either the record with the given ID doesn’t exist or the record didn’t meet the additional restrictions.

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.

Included Modules

ClassInheritableAttributes

ActiveRecord::Base (Class)

Creation

Conditions

Overwriting default accessors

Saving arrays, hashes, and other non-mappeable objects in text columns

Exceptions

Methods

Included Modules

Public Class methods

Public Instance methods

Private Instance methods

ActiveRecord::Base ^(Class)