Class | ActiveRecord::Base
In: | lib/active_record/base.rb lib/active_record/connection_adapters/abstract/connection_specification.rb lib/active_record/connection_adapters/mysql_adapter.rb lib/active_record/connection_adapters/postgresql_adapter.rb lib/active_record/connection_adapters/sqlite3_adapter.rb
lib/active_record/connection_adapters/sqlite_adapter.rb
Parent: | 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/README.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)
          find(:first, :conditions => "user_name = '#{user_name}' AND password = '#{password}'")
        end

        def self.authenticate_safely(user_name, password)
          find(:first, :conditions => [ "user_name = ? AND password = ?", user_name, password ])
        end

        def self.authenticate_safely_simply(user_name, password)
          find(:first, :conditions => { :user_name => user_name, :password => 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 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.find(:first, :conditions => [
        "id = :id AND name = :name AND division = :division AND created_at > :accounting_date",
        { :id => 3, :name => "37signals", :division => "First", :accounting_date => '2005-01-01' }
      ])

Similarly, a simple hash without a statement will generate conditions based on equality with the SQL AND operator. For instance:

      Student.find(:all, :conditions => { :first_name => "Harvey", :status => 1 })
      Student.find(:all, :conditions => params[:student])

A range may be used in the hash to use the SQL BETWEEN operator:

      Student.find(:all, :conditions => { :grade => 9..12 })

An array may be used in the hash to use the SQL IN operator:

      Student.find(:all, :conditions => { :grade => [9,11,12] })

## 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. Example:

      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)` as a shorter form.

## 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_` or `find_all_by_`, so you get finders like `Person.find_by_user_name`, `Person.find_all_by_last_name`, and `Payment.find_by_transaction_id`. So instead of writing `Person.find(:first, :conditions => ["user_name = ?", user_name])`, you just do `Person.find_by_user_name(user_name)`. And instead of writing `Person.find(:all, :conditions => ["last_name = ?", last_name])`, you just do `Person.find_all_by_last_name(last_name)`.

It‘s also possible to use multiple attributes in the same find by separating them with "and", so you get finders like `Person.find_by_user_name_and_password` or even `Payment.find_by_purchaser_and_state_and_country`. So instead of writing `Person.find(:first, :conditions => ["user_name = ? AND password = ?", user_name, password])`, you just do `Person.find_by_user_name_and_password(user_name, password)`.

It‘s even possible to use all the additional parameters to find. For example, the full interface for `Payment.find_all_by_amount` is actually `Payment.find_all_by_amount(amount, options)`. And the full interface to `Person.find_by_user_name` is actually `Person.find_by_user_name(user_name, options)`. So you could call `Payment.find_all_by_amount(50, :order => "created_on")`.

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. For example:

      # 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 `find_or_initialize_by_` finder if you want to return a new record without saving it first. Protected attributes won‘t be setted unless they are given in a block. For example:

      # No 'Winter' tag exists
      winter = Tag.find_or_initialize_by_name("Winter")
      winter.new_record? # true

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. For example:

      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.

## 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. Example:

      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 descendent of a class not in the hierarchy. Example:

      class User < ActiveRecord::Base
        serialize :preferences, Hash
      end

      user = User.create(:preferences => %w( one two three ))
      User.find(user.id).preferences    # raises SerializationTypeMismatch

## 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.find(:first, "name = ‘37signals’")` 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

- 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.

### Methods

== === [] []= abstract_class? aggregate_mapping all attr_accessible attr_protected attr_readonly attribute_for_inspect attribute_names attribute_present? attributes attributes= attributes_before_type_cast base_class becomes benchmark cache_key class_of_active_record_descendant clear_active_connections! clear_reloadable_connections! clone column_for_attribute column_names columns columns_hash compute_type connected? connection connection content_columns count_by_sql create decrement decrement! decrement_counter delete delete_all descends_from_active_record? destroy destroy destroy_all eql? establish_connection exists? expand_hash_conditions_for_aggregates find find_by_sql first freeze frozen? has_attribute? hash id id= increment increment! increment_counter inheritance_column inspect inspect last new new_record? primary_key readonly! readonly? readonly_attributes reload remove_connection require_mysql reset_column_information respond_to? sanitize_sql_array sanitize_sql_for_assignment sanitize_sql_for_conditions sanitize_sql_hash_for_assignment sanitize_sql_hash_for_conditions save save! serialize serialized_attributes set_inheritance_column set_primary_key set_sequence_name set_table_name silence sti_name table_exists? table_name to_param toggle toggle! update update_all update_attribute update_attributes update_attributes! update_counters with_exclusive_scope with_scope

### Constants

VALID_FIND_OPTIONS | = | [ :conditions, :include, :joins, :limit, :offset, :order, :select, :readonly, :group, :from, :lock ]

### External Aliases

set_table_name | -> | table_name=
set_primary_key | -> | primary_key=
set_inheritance_column | -> | inheritance_column=
set_sequence_name | -> | sequence_name=
sanitize_sql_for_conditions | -> | sanitize_sql
sanitize_sql_hash_for_conditions | -> | sanitize_sql_hash
sanitize_sql | -> | sanitize_conditions

### Attributes

abstract_class | [RW] | Set this to true if this is an abstract class (see `abstract_class?`).

### Public Class methods

===(object)

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

abstract_class?()

Returns whether this class is a base AR class. If A is a base class and B descends from A, then B.base_class will return B.

all(*args)

This is an alias for find(:all). You can pass in all the same arguments to this method as you can to find(:all)

attr_accessible(*attributes)

Specifies a white list of model attributes that can be set via mass-assignment, such as `new(attributes)`, `update_attributes(attributes)`, or `attributes=(attributes)`

This is the opposite of the `attr_protected` macro: Mass-assignment will only set attributes in this list, to assign to the rest of attributes you can use direct writer methods. This is meant to protect sensitive attributes from being overwritten by malicious users tampering with URLs or forms. If you‘d rather start from an all-open default and restrict attributes as needed, have a look at `attr_protected`.

      class Customer < ActiveRecord::Base
        attr_accessible :name, :nickname
      end

      customer = Customer.new(:name => "David", :nickname => "Dave", :credit_rating => "Excellent")
      customer.credit_rating # => nil
      customer.attributes = { :name => "Jolly fellow", :credit_rating => "Superb" }
      customer.credit_rating # => nil

      customer.credit_rating = "Average"
      customer.credit_rating # => "Average"

attr_protected(*attributes)

Attributes named in this macro are protected from mass-assignment, such as `new(attributes)`, `update_attributes(attributes)`, or `attributes=(attributes)`.

Mass-assignment to these attributes will simply be ignored, to assign to them you can use direct writer methods. This is meant to protect sensitive attributes from being overwritten by malicious users tampering with URLs or forms.

      class Customer < ActiveRecord::Base
        attr_protected :credit_rating
      end

      customer = Customer.new("name" => David, "credit_rating" => "Excellent")
      customer.credit_rating # => nil
      customer.attributes = { "description" => "Jolly fellow", "credit_rating" => "Superb" }
      customer.credit_rating # => nil

      customer.credit_rating = "Average"
      customer.credit_rating # => "Average"

To start from an all-closed default and enable attributes as needed, have a look at `attr_accessible`.

attr_readonly(*attributes)

Attributes listed as readonly can be set for a new record, but will be ignored in database updates afterwards.

base_class()

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.

benchmark(title, log_level = Logger::DEBUG, use_silence = true) {|| ...}

Log and benchmark multiple statements in a single block. Example:

      Project.benchmark("Creating project") do
        project = Project.create("name" => "stuff")
        project.create_manager("name" => "David")
        project.milestones << Milestone.find(:all)
      end

The benchmark is only recorded if the current level of the logger is less than or equal to the `log_level`, which makes it easy to include benchmarking statements in production software that will remain inexpensive because the benchmark will only be conducted if the log level is low enough.

The logging of the multiple statements is turned off unless `use_silence` is set to false.

clear_active_connections!()

Clears the cache which maps classes to connections.

clear_reloadable_connections!()

Clears the cache which maps classes

column_names()

Returns an array of column names as strings.

columns()

Returns an array of column objects for the table associated with this class.

columns_hash()

Returns a hash of column objects for the table associated with this class.

connected?()

Returns true if a connection that‘s accessible to this class has already been opened.

connection()

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.

content_columns()

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.

count_by_sql(sql)

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.

#### Attributes

- `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"

create(attributes = nil) {|object| ...}

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.

#### Examples

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

      # 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

decrement_counter(counter_name, id)

Decrement a number field by one, usually representing a count.

This works the same as increment_counter but reduces the column value by 1 instead of increasing it.

#### Attributes

- `counter_name` - The name of the field that should be decremented.
- `id` - The id of the object that should be decremented.

#### Examples

      # Decrement the post_count column for the record with an id of 5
      DiscussionBoard.decrement_counter(:post_count, 5)

delete(id)

Delete an object (or multiple objects) where the `id` given matches the primary_key. A SQL `DELETE` command is executed on the database which means that no callbacks are fired off running this. This is an efficient method of deleting records that don‘t need cleaning up after or other actions to be taken.

Objects are not instantiated with this method.

#### Attributes

- `id` - Can be either an Integer or an Array of Integers.

#### Examples

      # Delete a single object
      Todo.delete(1)

      # Delete multiple objects
      todos = [1,2,3]
      Todo.delete(todos)

delete_all(conditions = nil)

Deletes the records matching `conditions` without instantiating the records first, and hence not calling the destroy method and invoking callbacks. This is a single SQL query, much more efficient than destroy_all.

#### Attributes

- `conditions` - Conditions are specified the same way as with `find` method.

#### Example

      Post.delete_all "person_id = 5 AND (category = 'Something' OR category = 'Else')"

This deletes the affected posts all at once with a single DELETE query. If you need to destroy dependent associations or call your before_ or after_destroy callbacks, use the `destroy_all` method instead.

descends_from_active_record?()

True if this isn‘t a concrete subclass needing a STI type condition.

destroy(id)

Destroy an object (or multiple objects) that has the given id, the object is instantiated first, therefore all callbacks and filters are fired off before the object is deleted. This method is less efficient than ActiveRecord#delete but allows cleanup methods and other actions to be run.

This essentially finds the object (or multiple objects) with the given id, creates a new object from the attributes, and then calls destroy on it.

#### Attributes

- `id` - Can be either an Integer or an Array of Integers.

#### Examples

      # Destroy a single object
      Todo.destroy(1)

      # Destroy multiple objects
      todos = [1,2,3]
      Todo.destroy(todos)

destroy_all(conditions = nil)

Destroys the records matching `conditions` by instantiating each record and calling the destroy method. This means at least 2*N database queries to destroy N records, so avoid destroy_all if you are deleting many records. If you want to simply delete records without worrying about dependent associations or callbacks, use the much faster `delete_all` method instead.

#### Attributes

- `conditions` - Conditions are specified the same way as with `find` method.

#### Example

      Person.destroy_all "last_login < '2004-04-04'"

This loads and destroys each person one by one, including its dependent associations and before_ and after_destroy callbacks.

establish_connection(spec = nil)

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"
      )

The exceptions AdapterNotSpecified, AdapterNotFound and ArgumentError may be returned on an error.

exists?(id_or_conditions)

Checks whether a record exists in the database that matches conditions given. These conditions can either be a single integer representing a primary key id to be found, or a condition to be matched like using ActiveRecord#find.

The `id_or_conditions` parameter can be an Integer or a String if you want to search the primary key column of the table for a matching id, or if you‘re looking to match against a condition you can use an Array or a Hash.

Possible gotcha: You can‘t pass in a condition as a string e.g. "name = ‘Jamie’", this would be sanitized and then queried against the primary key column as "id = ‘name = \’Jamie"

#### Examples

      Person.exists?(5)
      Person.exists?('5')
      Person.exists?(:name => "David")
      Person.exists?(['name LIKE ?', "%#{query}%"])

find(*args)

Find operates with four different retrieval approaches:

- Find by id - This can either be a specific id (1), a list of ids (1, 5, 6), or an array of ids ([5, 6, 10]). If no record can be found for all of the listed ids, then RecordNotFound will be raised.
- Find first - This will return the first record matched by the options used. These options can either be specific conditions or merely an order. If no record can be matched, `nil` is returned. Use `Model.find(:first, *args)` or its shortcut `Model.first(*args)`.
- Find last - This will return the last record matched by the options used. These options can either be specific conditions or merely an order. If no record can be matched, `nil` is returned. Use `Model.find(:last, *args)` or its shortcut `Model.last(*args)`.
- Find all - This will return all the records matched by the options used. If no records are found, an empty array is returned. Use `Model.find(:all, *args)` or its shortcut `Model.all(*args)`.

All approaches accept an options hash as their last parameter.

#### Attributes

- `:conditions` - An SQL fragment like "administrator = 1" or `[ "user_name = ?", username ]`. See conditions in the intro.
- `:order` - An SQL fragment like "created_at DESC, name".
- `:group` - An attribute name by which the result should be grouped. Uses the `GROUP BY` SQL-clause.
- `:limit` - An integer determining the limit on the number of rows that should be returned.
- `:offset` - An integer determining the offset from where the rows should be fetched. So at 5, it would skip rows 0 through 4.
- `:joins` - Either an SQL fragment for additional joins like "LEFT JOIN comments ON comments.post_id = id" (rarely needed) or named associations in the same form used for the `:include` option, which will perform an `INNER JOIN` on the associated table(s). If the value is a string, then the records will be returned read-only since they will have attributes that do not correspond to the table‘s columns. Pass `:readonly => false` to override.
- `:include` - Names associations that should be loaded alongside. The symbols named refer to already defined associations. See eager loading under Associations.
- `:select` - By default, this is "*" as in "SELECT * FROM", but can be changed if you, for example, want to do a join but not include the joined columns.
- `:from` - By default, this is the table name of the class, but can be changed to an alternate table name (or even the name of a database view).
- `:readonly` - Mark the returned records read-only so they cannot be saved or updated.
- `:lock` - An SQL fragment like "FOR UPDATE" or "LOCK IN SHARE MODE". `:lock => true` gives connection‘s default exclusive lock, usually "FOR UPDATE".

#### Examples

      # find by id
      Person.find(1)       # returns the object for ID = 1
      Person.find(1, 2, 6) # returns an array for objects with IDs in (1, 2, 6)
      Person.find([7, 17]) # returns an array for objects with IDs in (7, 17)
      Person.find([1])     # returns an array for the object with ID = 1
      Person.find(1, :conditions => "administrator = 1", :order => "created_on DESC")

Note that returned records may not be in the same order as the ids you provide since database rows are unordered. Give an explicit `:order` to ensure the results are sorted.

#### Examples

      # find first
      Person.find(:first) # returns the first object fetched by SELECT * FROM people
      Person.find(:first, :conditions => [ "user_name = ?", user_name])
      Person.find(:first, :order => "created_on DESC", :offset => 5)

      # find last
      Person.find(:last) # returns the last object fetched by SELECT * FROM people
      Person.find(:last, :conditions => [ "user_name = ?", user_name])
      Person.find(:last, :order => "created_on DESC", :offset => 5)

      # find all
      Person.find(:all) # returns an array of objects for all the rows fetched by SELECT * FROM people
      Person.find(:all, :conditions => [ "category IN (?)", categories], :limit => 50)
      Person.find(:all, :conditions => { :friends => ["Bob", "Steve", "Fred"] }
      Person.find(:all, :offset => 10, :limit => 10)
      Person.find(:all, :include => [ :account, :friends ])
      Person.find(:all, :group => "category")

Example for find with a lock: Imagine two concurrent transactions: each will read `person.visits == 2`, add 1 to it, and save, resulting in two saves of `person.visits = 3`. By locking the row, the second transaction has to wait until the first is finished; we get the expected `person.visits == 4`.

      Person.transaction do
        person = Person.find(1, :lock => true)
        person.visits += 1
        person.save!
      end

find_by_sql(sql)

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 +Product.find_by_sql+ 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={"first_name"=>"The Cheap Man Buys Twice"}>, ...]

first(*args)

A convenience wrapper for `find(:first, *args)`. You can pass in all the same arguments to this method as you can to `find(:first)`.

increment_counter(counter_name, id)

Increment a number field by one, usually representing a count.

This is used for caching aggregate values, so that they don‘t need to be computed every time. For example, a DiscussionBoard may cache post_count and comment_count otherwise every time the board is shown it would have to run an SQL query to find how many posts and comments there are.

#### Attributes

- `counter_name` - The name of the field that should be incremented.
- `id` - The id of the object that should be incremented.

#### Examples

      # Increment the post_count column for the record with an id of 5
      DiscussionBoard.increment_counter(:post_count, 5)

inheritance_column()

Defines the column name for use with single table inheritance — can be set in subclasses like so: self.inheritance_column = "type_id"

inspect()

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

last(*args)

A convenience wrapper for `find(:last, *args)`. You can pass in all the same arguments to this method as you can to `find(:last)`.

new(attributes = nil) {|self if block_given?| ...}

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.

primary_key()

Defines the primary key field — can be overridden in subclasses. Overwriting will negate any effect of the primary_key_prefix_type setting, though.

readonly_attributes()

Returns an array of all the attributes that have been specified as readonly.

remove_connection(klass=self)

Remove the connection for this class. This will close the active connection and the defined connection (if they exist). The result can be used as an argument for establish_connection, for easily re-establishing the connection.

require_mysql()
reset_column_information()

Resets all the cached information about columns, which will cause them to be reloaded on the next request.

respond_to?(method_id, include_private = false)
serialize(attr_name, class_name = Object)

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.

#### Attributes

- `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
        serialize :preferences
      end

serialized_attributes()

Returns a hash of all the attributes that have been specified for serialization as keys and their class restriction as values.

set_inheritance_column(value = nil, &block)

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

set_primary_key(value = nil, &block)

Sets the name of the primary key 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_primary_key "sysid"
      end

set_sequence_name(value = nil, &block)

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

set_table_name(value = nil, &block)

Sets the table name 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_table_name "project"
      end

silence() {|| ...}

Silences the logger for the duration of the block.

sti_name()
table_exists?()

Indicates whether the table associated with this class exists

table_name()

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

update(id, attributes)

Updates 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.

#### Attributes

- `id` - This should be the id or an array of ids to be updated.
- `attributes` - This should be a Hash of attributes to be set on the object, or an array of Hashes.

#### Examples

      # Updating one record:
      Person.update(15, { :user_name => 'Samuel', :group => 'expert' })

      # Updating multiple records:
      people = { 1 => { "first_name" => "David" }, 2 => { "first_name" => "Jeremy" } }
      Person.update(people.keys, people.values)

update_all(updates, conditions = nil, options = {})

Updates all records with details given if they match a set of conditions supplied, limits and order can also be supplied.

#### Attributes

- `updates` - A String of column and value pairs that will be set on any records that match conditions.
- `conditions` - An SQL fragment like "administrator = 1" or [ "user_name = ?", username ]. See conditions in the intro for more info.
- `options` - Additional options are `:limit` and/or `:order`, see the examples for usage.

#### Examples

      # Update all billing objects with the 3 different attributes given
      Billing.update_all( "category = 'authorized', approved = 1, author = 'David'" )

      # Update records that match our conditions
      Billing.update_all( "author = 'David'", "title LIKE '%Rails%'" )

      # Update records that match our conditions but limit it to 5 ordered by date
      Billing.update_all( "author = 'David'", "title LIKE '%Rails%'",
                            :order => 'created_at', :limit => 5 )

update_counters(id, counters)

A generic "counter updater" implementation, intended primarily to be used by increment_counter and decrement_counter, but which may also be useful on its own. It simply does a direct SQL update for the record with the given ID, altering the given hash of counters by the amount given by the corresponding value:

#### Attributes

- `id` - The id of the object you wish to update a counter on.
- `counters` - An Array of Hashes containing the names of the fields to update as keys and the amount to update the field by as values.

#### Examples

      # For the Post with id of 5, decrement the comment_count by 1, and
      # increment the action_count by 1
      Post.update_counters 5, :comment_count => -1, :action_count => 1
      # Executes the following SQL:
      # UPDATE posts
      #    SET comment_count = comment_count - 1,
      #        action_count = action_count + 1
      #  WHERE id = 5

### Protected Class methods

aggregate_mapping(reflection)
class_of_active_record_descendant(klass)

Returns the class descending directly from Active Record in the inheritance hierarchy.

compute_type(type_name)

Returns the class type of the record using the current module as a prefix. So descendents of MyApp::Business::Account would appear as MyApp::Business::AccountSubclass.

expand_hash_conditions_for_aggregates(attrs)

Accepts a hash of SQL conditions and replaces those attributes that correspond to a `composed_of` relationship with their expanded aggregate attribute values. Given:

        class Person < ActiveRecord::Base
          composed_of :address, :class_name => "Address",
            :mapping => [%w(address_street street), %w(address_city city)]
        end

Then:

        { :address => Address.new("813 abc st.", "chicago") }
          # => { :address_street => "813 abc st.", :address_city => "chicago" }

sanitize_sql_array(ary)

Accepts an array of conditions. The array has each value sanitized and interpolated into the SQL statement.

      ["name='%s' and group_id='%s'", "foo'bar", 4]  returns  "name='foo''bar' and group_id='4'"

sanitize_sql_for_assignment(assignments)

Accepts an array, hash, or string of SQL conditions and sanitizes them into a valid SQL fragment for a SET clause.

      { :name => nil, :group_id => 4 }  returns "name = NULL , group_id='4'"

sanitize_sql_for_conditions(condition)

Accepts an array, hash, or string of SQL conditions and sanitizes them into a valid SQL fragment for a WHERE clause.

      ["name='%s' and group_id='%s'", "foo'bar", 4]  returns  "name='foo''bar' and group_id='4'"
      { :name => "foo'bar", :group_id => 4 }  returns "name='foo''bar' and group_id='4'"
      "name='foo''bar' and group_id='4'" returns "name='foo''bar' and group_id='4'"

sanitize_sql_hash_for_assignment(attrs)

Sanitizes a hash of attribute/value pairs into SQL conditions for a SET clause.

      { :status => nil, :group_id => 1 }
        # => "status = NULL , group_id = 1"

sanitize_sql_hash_for_conditions(attrs)

Sanitizes a hash of attribute/value pairs into SQL conditions for a WHERE clause.

      { :name => "foo'bar", :group_id => 4 }
        # => "name='foo''bar' and group_id= 4"
      { :status => nil, :group_id => [1,2,3] }
        # => "status IS NULL and group_id IN (1,2,3)"
      { :age => 13..18 }
        # => "age BETWEEN 13 AND 18"
      { 'other_records.id' => 7 }
        # => "`other_records`.`id` = 7"

And for value objects on a composed_of relationship:

      { :address => Address.new("123 abc st.", "chicago") }
        # => "address_street='123 abc st.' and address_city='chicago'"

with_exclusive_scope(method_scoping = {}, &block)

Works like with_scope, but discards any nested properties.

with_scope(method_scoping = {}, action = :merge) {|| ...}

Scope parameters to method calls within the block. Takes a hash of method_name => parameters hash. method_name may be `:find` or `:create`. `:find` parameters may include the `:conditions`, `:joins`, `:include`, `:offset`, `:limit`, and `:readonly` options. `:create` parameters are an attributes hash.

      class Article < ActiveRecord::Base
        def self.create_with_scope
          with_scope(:find => { :conditions => "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 `:conditions` and `:include` options in `:find`, which are merged.

      class Article < ActiveRecord::Base
        def self.find_with_scope
          with_scope(:find => { :conditions => "blog_id = 1", :limit => 1 }, :create => { :blog_id => 1 }) do
            with_scope(:find => { :limit => 10 })
              find(:all) # => SELECT * from articles WHERE blog_id = 1 LIMIT 10
            end
            with_scope(:find => { :conditions => "author_id = 3" })
              find(: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 `with_exclusive_scope` method.

      class Article < ActiveRecord::Base
        def self.find_with_exclusive_scope
          with_scope(:find => { :conditions => "blog_id = 1", :limit => 1 }) do
            with_exclusive_scope(:find => { :limit => 10 })
              find(:all) # => SELECT * from articles LIMIT 10
            end
          end
        end
      end

### Public Instance methods

==(comparison_object)

Returns true if the `comparison_object` is the same object, or is of the same type and has the same id.

[](attr_name)

Returns the value of the attribute identified by `attr_name` after it has been typecast (for example, "2004-12-12" in a data column is cast to a date object, like Date.new(2004, 12, 12)). (Alias for the protected read_attribute method).

[]=(attr_name, value)

Updates the attribute identified by `attr_name` with the specified `value`. (Alias for the protected write_attribute method).

attribute_for_inspect(attr_name)

Format attributes nicely for inspect.

attribute_names()

Returns an array of names for the attributes available on this object sorted alphabetically.

attribute_present?(attribute)

Returns true if the specified `attribute` has been set by the user or by a database load and is neither nil nor empty? (the latter only applies to objects that respond to empty?, most notably Strings).

attributes()

Returns a hash of all the attributes with their names as keys and the values of the attributes as values.

attributes=(new_attributes, guard_protected_attributes = true)

Allows you to set all the attributes at once by passing in a hash with keys matching the attribute names (which again matches the column names). Sensitive attributes can be protected from this form of mass-assignment by using the `attr_protected` macro. Or you can alternatively specify which attributes can be accessed with the `attr_accessible` macro. Then all the attributes not included in that won‘t be allowed to be mass-assigned.

attributes_before_type_cast()

Returns a hash of attributes before typecasting and deserialization.

becomes(klass)

Returns an instance of the specified `klass` with the attributes of the current record. This is mostly useful in relation to single-table inheritance structures where you want a subclass to appear as the superclass. This can be used along with record identification in Action Pack to allow, say, `Client < Company` to do something like render `:partial => @client.becomes(Company)` to render that instance using the companies/company partial instead of clients/client.

Note: The new instance will share a link to the same attributes as the original class. So any change to the attributes in either instance will affect the other.

cache_key()

Returns a cache key that can be used to identify this record.

#### Examples

      Product.new.cache_key     # => "products/new"
      Product.find(5).cache_key # => "products/5" (updated_at not available)
      Person.find(5).cache_key  # => "people/5-20071224150000" (updated_at available)

clone()

Returns a clone of the record that hasn‘t been assigned an id yet and is treated as a new record. Note that this is a "shallow" clone: it copies the object‘s attributes only, not its associations. The extent of a "deep" clone is application-specific and is therefore left to the application to implement according to its need.

column_for_attribute(name)

Returns the column object for the named attribute.

connection()

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.

decrement(attribute, by = 1)

Initializes `attribute` to zero if `nil` and subtracts the value passed as `by` (default is 1). The decrement is performed directly on the underlying attribute, no setter is invoked. Only makes sense for number-based attributes. Returns `self`.

decrement!(attribute, by = 1)

Wrapper around `decrement` that saves the record. This method differs from its non-bang version in that it passes through the attribute setter. Saving is not subjected to validation checks. Returns `true` if the record could be saved.

destroy()

Deletes the record in the database and freezes this instance to reflect that no changes should be made (since they can‘t be persisted).

eql?(comparison_object)

Delegates to ==

freeze()

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

frozen?()

Returns `true` if the attributes hash has been frozen.

has_attribute?(attr_name)

Returns true if the given attribute is in the attributes hash

hash()

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) ]

id()

A model instance‘s primary key is always available as model.id whether you name it the default ‘id’ or set it to something else.

id=(value)

Sets the primary ID.

increment(attribute, by = 1)

Initializes `attribute` to zero if `nil` and adds the value passed as `by` (default is 1). The increment is performed directly on the underlying attribute, no setter is invoked. Only makes sense for number-based attributes. Returns `self`.

increment!(attribute, by = 1)

Wrapper around `increment` that saves the record. This method differs from its non-bang version in that it passes through the attribute setter. Saving is not subjected to validation checks. Returns `true` if the record could be saved.

inspect()

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

new_record?()

Returns true if this object hasn‘t been saved yet — that is, a record for the object doesn‘t exist yet.

readonly!()

Marks this record as read only.

readonly?()

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.

reload(options = nil)

Reloads the attributes of this object from the database. The optional options argument is passed to find when reloading so you may do e.g. record.reload(:lock => true) to reload the same record with an exclusive row lock.

save()

- No record exists: Creates a new record with values matching those of the object attributes.
- A record does exist: Updates the record with values matching those of the object attributes.

Note: If your model specifies any validations then the method declaration dynamically changes to:

      save(perform_validation=true)

Calling save(false) saves the model without running validations. See ActiveRecord::Validations for more information.

save!()

Attempts to save the record, but instead of just returning false if it couldn‘t happen, it raises a RecordNotSaved exception

to_param()

Enables Active Record objects to be used as URL parameters in Action Pack automatically.

toggle(attribute)

Assigns to `attribute` the boolean opposite of `attribute?`. So if the predicate returns `true` the attribute will become `false`. This method toggles directly the underlying value without calling any setter. Returns `self`.

toggle!(attribute)

Wrapper around `toggle` that saves the record. This method differs from its non-bang version in that it passes through the attribute setter. Saving is not subjected to validation checks. Returns `true` if the record could be saved.

update_attribute(name, value)

Updates a single attribute and saves the record. This is especially useful for boolean flags on existing records. Note: This method is overwritten by the Validation module that‘ll make sure that updates made with this method aren‘t subjected to validation checks. Hence, attributes can be updated even if the full object isn‘t valid.

update_attributes(attributes)

Updates all the attributes from the passed-in Hash and saves the record. If the object is invalid, the saving will fail and false will be returned.

update_attributes!(attributes)

Updates an object just like Base.update_attributes but calls save! instead of save so an exception is raised if the record is invalid.

[Validate]