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 => { :type => 'public' }) Student.joins(:schools).where('schools.type' => '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 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 }
Use the find_or_initialize_by_ finder if you want to return a new record without saving it first. Protected attributes won’t be set unless they are given in a block.
# No 'Winter' tag exists winter = Tag.find_or_initialize_by_name("Winter") winter.persisted? # false
To find by a subset of the attributes to be used for instantiating a new object, pass a hash instead of a list of parameters.
Tag.find_or_create_by_name(:name => "rails", :creator => current_user)
That will either find an existing tag named “rails”, or create a new one while setting the user that created it.
Just like find_by_*, you can also use scoped_by_* to retrieve data. The good thing about using this feature is that the very first time result is returned using method_missing technique but after that the method is declared on the class. Henceforth method_missing will not be hit.
User.scoped_by_user_name('David')
Saving arrays, hashes, and other non-mappable objects in text columns
Active Record can serialize any object in text columns using YAML. To do so, you must specify this with a call to the class method serialize. This makes it possible to store arrays, hashes, and other non-mappable objects without doing any additional work.
class User < ActiveRecord::Base serialize :preferences end user = User.create(:preferences => { "background" => "black", "display" => large }) User.find(user.id).preferences # => { "background" => "black", "display" => large }
You can also specify a class option as the second parameter that’ll raise an exception if a serialized object is retrieved as a descendant of a class not in the hierarchy.
class User < ActiveRecord::Base serialize :preferences, Hash end user = User.create(:preferences => %w( one two three )) User.find(user.id).preferences # raises SerializationTypeMismatch
When you specify a class option, the default value for that attribute will be a new instance of that class.
class User < ActiveRecord::Base serialize :preferences, OpenStruct end user = User.new user.preferences.theme_color = "red"
Single table inheritance
Active Record allows inheritance by storing the name of the class in a column that by default is named “type” (can be changed by overwriting Base.inheritance_column). This means that an inheritance looking like this:
class Company < ActiveRecord::Base; end class Firm < Company; end class Client < Company; end class PriorityClient < Client; end
When you do Firm.create(:name => "37signals"), this record will be saved in the companies table with type = “Firm”. You can then fetch this row again using Company.where(:name => '37signals').first and it will return a Firm object.
If you don’t have a type column defined in your table, single-table inheritance won’t be triggered. In that case, it’ll work just like normal subclasses with no special magic for differentiating between them or reloading the right type with find.
Note, all the attributes for all the cases are kept in the same table. Read more: www.martinfowler.com/eaaCatalog/singleTableInheritance.html
Connection to multiple databases in different models
Connections are usually created through ActiveRecord::Base.establish_connection and retrieved by ActiveRecord::Base.connection. All classes inheriting from ActiveRecord::Base will use this connection. But you can also set a class-specific connection. For example, if Course is an ActiveRecord::Base, but resides in a different database, you can just say Course.establish_connection and Course and all of its subclasses will use this connection instead.
This feature is implemented by keeping a connection pool in ActiveRecord::Base that is a Hash indexed by the class. If a connection is requested, the retrieve_connection method will go up the class-hierarchy until a connection is found in the connection pool.
Exceptions
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ActiveRecordError - Generic error class and superclass of all other errors raised by Active Record.
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AdapterNotSpecified - The configuration hash used in establish_connection didn’t include an :adapter key.
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AdapterNotFound - The :adapter key used in establish_connection specified a non-existent adapter (or a bad spelling of an existing one).
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AssociationTypeMismatch - The object assigned to the association wasn’t of the type specified in the association definition.
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SerializationTypeMismatch - The serialized object wasn’t of the class specified as the second parameter.
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ConnectionNotEstablished+ - No connection has been established. Use establish_connection before querying.
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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.
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StatementInvalid - The database server rejected the SQL statement. The precise error is added in the message.
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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.
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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.
- #
- A
- B
- C
-
- cache_key,
- class_of_active_record_descendant,
- clear_active_connections!,
- clone_attribute_value,
- clone_attributes,
- column_defaults,
- column_for_attribute,
- column_names,
- columns,
- columns_hash,
- compute_type,
- configurations,
- connected?,
- connection,
- connection,
- connection_config,
- connection_handler,
- connection_pool,
- content_columns,
- count_by_sql,
- create
- D
- E
- F
- H
- I
- L
- M
- N
- P
- Q
- R
- S
-
- sanitize_conditions,
- sanitize_sql,
- sanitize_sql_array,
- sanitize_sql_for_assignment,
- sanitize_sql_for_conditions,
- sanitize_sql_hash,
- sanitize_sql_hash_for_assignment,
- sanitize_sql_hash_for_conditions,
- schema_format,
- sequence_name=,
- serialize,
- set_inheritance_column,
- set_sequence_name,
- set_table_name,
- sti_name,
- symbolized_base_class,
- symbolized_sti_name
- T
- W
[RW] | abstract_class | Set this to true if this is an abstract class (see abstract_class?). |
Overwrite the default class equality method to provide support for association proxies.
Returns whether this class is an abstract class or not.
Attributes listed as readonly will be used to create a new record but update operations will ignore these fields.
Returns an array of column names as strings if it’s not an abstract class and table exists. Otherwise it returns an empty array.
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.
If B < A and C < B and if A is an abstract_class then both B.base_class and C.base_class would return B as the answer since A is an abstract_class.
Returns a hash where the keys are column names and the values are default values when instantiating the AR object for this table.
Returns an array of column names as strings.
Returns an array of column objects for the table associated with this class.
Returns a hash of column objects for the table associated with this class.
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' } }
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
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.
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.
Parameters
-
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"
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.
create respects mass-assignment security and accepts either :as or :without_protection options in the options parameter.
Examples
# Create a single new object User.create(:first_name => 'Jamie') # Create a single new object using the :admin mass-assignment security role User.create({ :first_name => 'Jamie', :is_admin => true }, :as => :admin) # Create a single new object bypassing mass-assignment security User.create({ :first_name => 'Jamie', :is_admin => true }, :without_protection => true) # 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
# File activerecord/lib/active_record/base.rb, line 504 def create(attributes = nil, options = {}, &block) if attributes.is_a?(Array) attributes.collect { |attr| create(attr, options, &block) } else object = new(attributes, options) yield(object) if block_given? object.save object end 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.
True if this isn’t a concrete subclass needing a STI type condition.
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.
# File activerecord/lib/active_record/connection_adapters/abstract/connection_specification.rb, line 51 def self.establish_connection(spec = nil) case spec when nil raise AdapterNotSpecified unless defined?(Rails.env) establish_connection(Rails.env) when ConnectionSpecification self.connection_handler.establish_connection(name, spec) when Symbol, String if configuration = configurations[spec.to_s] establish_connection(configuration) else raise AdapterNotSpecified, "#{spec} database is not configured" end else spec = spec.symbolize_keys unless spec.key?(:adapter) then raise AdapterNotSpecified, "database configuration does not specify adapter" end begin require "active_record/connection_adapters/#{spec[:adapter]}_adapter" rescue LoadError => e raise "Please install the #{spec[:adapter]} adapter: `gem install activerecord-#{spec[:adapter]}-adapter` (#{e})" end adapter_method = "#{spec[:adapter]}_connection" unless respond_to?(adapter_method) raise AdapterNotFound, "database configuration specifies nonexistent #{spec[:adapter]} adapter" end remove_connection establish_connection(ConnectionSpecification.new(spec, adapter_method)) end end
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={"title"=>"The Cheap Man Buys Twice"}>, ...]
Defines the column name for use with single table inheritance. Use set_inheritance_column to set a different value.
Returns a string like ‘Post(id:integer, title:string, body:text)’
# File activerecord/lib/active_record/base.rb, line 831 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
Finder methods must instantiate through this method to work with the single-table inheritance model that makes it possible to create objects of different types from the same table.
# File activerecord/lib/active_record/base.rb, line 946 def instantiate(record) sti_class = find_sti_class(record[inheritance_column]) record_id = sti_class.primary_key && record[sti_class.primary_key] if ActiveRecord::IdentityMap.enabled? && record_id if (column = sti_class.columns_hash[sti_class.primary_key]) && column.number? record_id = record_id.to_i end if instance = IdentityMap.get(sti_class, record_id) instance.reinit_with('attributes' => record) else instance = sti_class.allocate.init_with('attributes' => record) IdentityMap.add(instance) end else instance = sti_class.allocate.init_with('attributes' => record) end instance 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 8 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 1543 def initialize(attributes = nil, options = {}) @attributes = attributes_from_column_definition @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 set_serialized_attributes populate_with_current_scope_attributes assign_attributes(attributes, options) if attributes yield self if block_given? run_callbacks :initialize end
Indicates whether table names should be the pluralized versions of the corresponding class names. If true, the default table name for a Product class will be products. If false, it would just be product. See table_name for the full rules on table/class naming. This is true, by default.
Accessor for the prefix type that will be prepended to every primary key column name. The options are :table_name and :table_name_with_underscore. If the first is specified, the Product class will look for “productid” instead of “id” as the primary column. If the latter is specified, the Product class will look for “product_id” instead of “id”. Remember that this is a global setting for all Active Records.
Returns a quoted version of the table name, used to construct SQL statements.
Returns an array of all the attributes that have been specified as readonly.
Resets all the cached information about columns, which will cause them to be reloaded on the next request.
The most common usage pattern for this method is probably in a migration, when just after creating a table you want to populate it with some default values, eg:
class CreateJobLevels < ActiveRecord::Migration def self.up create_table :job_levels do |t| t.integer :id t.string :name t.timestamps end JobLevel.reset_column_information %w{assistant executive manager director}.each do |type| JobLevel.create(:name => type) end end def self.down drop_table :job_levels end end
# File activerecord/lib/active_record/base.rb, line 771 def reset_column_information connection.clear_cache! undefine_attribute_methods connection_pool.clear_table_cache!(table_name) if table_exists? @column_names = @content_columns = @dynamic_methods_hash = @inheritance_column = nil @arel_engine = @relation = nil end
# File activerecord/lib/active_record/base.rb, line 884 def respond_to?(method_id, include_private = false) if match = DynamicFinderMatch.match(method_id) return true if all_attributes_exists?(match.attribute_names) elsif match = DynamicScopeMatch.match(method_id) return true if all_attributes_exists?(match.attribute_names) end super 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.
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.
Parameters
-
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 < ActiveRecord::Base serialize :preferences end
# File activerecord/lib/active_record/base.rb, line 557 def serialize(attr_name, class_name = Object) coder = if [:load, :dump].all? { |x| class_name.respond_to?(x) } class_name else Coders::YAMLColumn.new(class_name) end # merge new serialized attribute and create new hash to ensure that each class in inheritance hierarchy # has its own hash of own serialized attributes self.serialized_attributes = serialized_attributes.merge(attr_name.to_s => coder) end
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
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
Sets the table name. If the value is nil or false then the value returned by the given block is used.
class Project < ActiveRecord::Base set_table_name "project" end
# File activerecord/lib/active_record/base.rb, line 656 def set_table_name(value = nil, &block) @quoted_table_name = nil define_attr_method :table_name, value, &block @arel_table = nil @arel_table = Arel::Table.new(table_name, arel_engine) @relation = Relation.new(self, arel_table) end
Indicates whether the table associated with this class exists
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
Accessor for the name of the prefix string to prepend to every table name. So if set to “basecamp_”, all table names will be named like “basecamp_projects”, “basecamp_people”, etc. This is a convenient way of creating a namespace for tables in a shared database. By default, the prefix is the empty string.
If you are organising your models within modules you can add a prefix to the models within a namespace by defining a singleton method in the parent module called table_name_prefix which returns your chosen prefix.
Works like table_name_prefix, but appends instead of prepends (set to “_basecamp” gives “projects_basecamp”, “people_basecamp”). By default, the suffix is the empty string.
Specify whether or not to use timestamps for migration versions
Returns the class descending directly from ActiveRecord::Base or an abstract class, if any, in the inheritance hierarchy.
# File activerecord/lib/active_record/base.rb, line 1341 def class_of_active_record_descendant(klass) if klass.superclass == Base || klass.superclass.abstract_class? klass elsif klass.superclass.nil? raise ActiveRecordError, "#{name} doesn't belong in a hierarchy descending from ActiveRecord" else class_of_active_record_descendant(klass.superclass) end end
Returns the class type of the record using the current module as a prefix. So descendants of MyApp::Business::Account would appear as MyApp::Business::AccountSubclass.
# File activerecord/lib/active_record/base.rb, line 1314 def compute_type(type_name) if type_name.match(/^::/) # If the type is prefixed with a scope operator then we assume that # the type_name is an absolute reference. ActiveSupport::Dependencies.constantize(type_name) else # Build a list of candidates to search for candidates = [] name.scan(/::|$/) { candidates.unshift "#{$`}::#{type_name}" } candidates << type_name candidates.each do |candidate| begin constant = ActiveSupport::Dependencies.constantize(candidate) return constant if candidate == constant.to_s rescue NameError => e # We don't want to swallow NoMethodError < NameError errors raise e unless e.instance_of?(NameError) end end raise NameError, "uninitialized constant #{candidates.first}" end end
Use this macro in your model to set a default scope for all operations on the model.
class Article < ActiveRecord::Base default_scope where(:published => true) end Article.all # => SELECT * FROM articles WHERE published = true
The default_scope is also applied while creating/building a record. It is not applied while updating a record.
Article.new.published # => true Article.create.published # => true
You can also use default_scope with a block, in order to have it lazily evaluated:
class Article < ActiveRecord::Base default_scope { where(:published_at => Time.now - 1.week) } end
(You can also pass any object which responds to call to the default_scope macro, and it will be called when building the default scope.)
If you use multiple default_scope declarations in your model then they will be merged together:
class Article < ActiveRecord::Base default_scope where(:published => true) default_scope where(:rating => 'G') end Article.all # => SELECT * FROM articles WHERE published = true AND rating = 'G'
This is also the case with inheritance and module includes where the parent or module defines a default_scope and the child or including class defines a second one.
If you need to do more complex things with a default scope, you can alternatively define it as a class method:
class Article < ActiveRecord::Base def self.default_scope # Should return a scope, you can call 'super' here etc. end end
The ignore_default_scope flag is used to prevent an infinite recursion situation where a default scope references a scope which has a default scope which references a scope…
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" }
# File activerecord/lib/active_record/base.rb, line 1394 def expand_hash_conditions_for_aggregates(attrs) expanded_attrs = {} attrs.each do |attr, value| unless (aggregation = reflect_on_aggregation(attr.to_sym)).nil? mapping = aggregate_mapping(aggregation) mapping.each do |field_attr, aggregate_attr| if mapping.size == 1 && !value.respond_to?(aggregate_attr) expanded_attrs[field_attr] = value else expanded_attrs[field_attr] = value.send(aggregate_attr) end end else expanded_attrs[attr] = value end end expanded_attrs end
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'"
# File activerecord/lib/active_record/base.rb, line 1449 def sanitize_sql_array(ary) statement, *values = ary if values.first.is_a?(Hash) && statement =~ /:\w+/ replace_named_bind_variables(statement, values.first) elsif statement.include?('?') replace_bind_variables(statement, values) elsif statement.blank? statement else statement % values.collect { |value| connection.quote_string(value.to_s) } end end
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'"
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'"
# File activerecord/lib/active_record/base.rb, line 1356 def sanitize_sql_for_conditions(condition, table_name = self.table_name) return nil if condition.blank? case condition when Array; sanitize_sql_array(condition) when Hash; sanitize_sql_hash_for_conditions(condition, table_name) else condition end end
Sanitizes a hash of attribute/value pairs into SQL conditions for a SET clause.
{ :status => nil, :group_id => 1 } # => "status = NULL , group_id = 1"
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" { :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'"
# File activerecord/lib/active_record/base.rb, line 1427 def sanitize_sql_hash_for_conditions(attrs, default_table_name = self.table_name) attrs = expand_hash_conditions_for_aggregates(attrs) table = Arel::Table.new(table_name).alias(default_table_name) PredicateBuilder.build_from_hash(arel_engine, attrs, table).map { |b| connection.visitor.accept b }.join(' AND ') end
Works like with_scope, but discards any nested properties.
# File activerecord/lib/active_record/base.rb, line 1197 def with_exclusive_scope(method_scoping = {}, &block) if method_scoping.values.any? { |e| e.is_a?(ActiveRecord::Relation) } raise ArgumentError, New finder API can not be used with_exclusive_scope. You can either call unscoped to get an anonymous scope not bound to the default_scope: User.unscoped.where(:active => true)Or call unscoped with a block: User.unscoped do User.where(:active => true).all end end with_scope(method_scoping, :overwrite, &block) end
with_scope lets you apply options to inner block incrementally. It takes a hash and the keys must be :find or :create. :find parameter is Relation while :create parameters are an attributes hash.
class Article < ActiveRecord::Base def self.create_with_scope with_scope(:find => where(: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 where, includes, and joins operations in Relation, which are merged.
joins operations are uniqued so multiple scopes can join in the same table without table aliasing problems. If you need to join multiple tables, but still want one of the tables to be uniqued, use the array of strings format for your joins.
class Article < ActiveRecord::Base def self.find_with_scope with_scope(:find => where(:blog_id => 1).limit(1), :create => { :blog_id => 1 }) do with_scope(:find => limit(10)) do all # => SELECT * from articles WHERE blog_id = 1 LIMIT 10 end with_scope(:find => where(:author_id => 3)) do 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 => where(:blog_id => 1).limit(1)) do with_exclusive_scope(:find => limit(10)) do all # => SELECT * from articles LIMIT 10 end end end end
Note: the :find scope also has effect on update and deletion methods, like update_all and delete_all.
# File activerecord/lib/active_record/base.rb, line 1152 def with_scope(scope = {}, action = :merge, &block) # If another Active Record class has been passed in, get its current scope scope = scope.current_scope if !scope.is_a?(Relation) && scope.respond_to?(:current_scope) previous_scope = self.current_scope if scope.is_a?(Hash) # Dup first and second level of hash (method and params). scope = scope.dup scope.each do |method, params| scope[method] = params.dup unless params == true end scope.assert_valid_keys([ :find, :create ]) relation = construct_finder_arel(scope[:find] || {}) relation.default_scoped = true unless action == :overwrite if previous_scope && previous_scope.create_with_value && scope[:create] scope_for_create = if action == :merge previous_scope.create_with_value.merge(scope[:create]) else scope[:create] end relation = relation.create_with(scope_for_create) else scope_for_create = scope[:create] scope_for_create ||= previous_scope.create_with_value if previous_scope relation = relation.create_with(scope_for_create) if scope_for_create end scope = relation end scope = previous_scope.merge(scope) if previous_scope && action == :merge self.current_scope = scope begin yield ensure self.current_scope = previous_scope end end
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.
Allows you to set all the attributes for a particular mass-assignment security role by passing in a hash of attributes with keys matching the attribute names (which again matches the column names) and the role name using the :as option.
To bypass mass-assignment security you can use the :without_protection => true option.
class User < ActiveRecord::Base attr_accessible :name attr_accessible :name, :is_admin, :as => :admin end user = User.new user.assign_attributes({ :name => 'Josh', :is_admin => true }) user.name # => "Josh" user.is_admin? # => false user = User.new user.assign_attributes({ :name => 'Josh', :is_admin => true }, :as => :admin) user.name # => "Josh" user.is_admin? # => true user = User.new user.assign_attributes({ :name => 'Josh', :is_admin => true }, :without_protection => true) user.name # => "Josh" user.is_admin? # => true
# File activerecord/lib/active_record/base.rb, line 1730 def assign_attributes(new_attributes, options = {}) return unless new_attributes attributes = new_attributes.stringify_keys multi_parameter_attributes = [] @mass_assignment_options = options unless options[:without_protection] attributes = sanitize_for_mass_assignment(attributes, mass_assignment_role) end attributes.each do |k, v| if k.include?("(") multi_parameter_attributes << [ k, v ] elsif respond_to?("#{k}=") send("#{k}=", v) else raise(UnknownAttributeError, "unknown attribute: #{k}") end end @mass_assignment_options = nil assign_multiparameter_attributes(multi_parameter_attributes) end
Returns an #inspect-like string for the value of the attribute attr_name. String attributes are truncated upto 50 characters, and Date and Time attributes are returned in the :db format. Other attributes return the value of #inspect without modification.
person = Person.create!(:name => "David Heinemeier Hansson " * 3) person.attribute_for_inspect(:name) # => '"David Heinemeier Hansson David Heinemeier Hansson D..."' person.attribute_for_inspect(:created_at) # => '"2009-01-12 04:48:57"'
# File activerecord/lib/active_record/base.rb, line 1773 def attribute_for_inspect(attr_name) value = read_attribute(attr_name) if value.is_a?(String) && value.length > 50 "#{value[0..50]}...".inspect elsif value.is_a?(Date) || value.is_a?(Time) %("#{value.to_s(:db)}") else value.inspect end end
Returns an array of names for the attributes available on this object.
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).
Returns a hash of all the attributes with their names as keys and the values of the attributes as values.
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).
If any attributes are protected by either attr_protected or attr_accessible then only settable attributes will be assigned.
The guard_protected_attributes argument is now deprecated, use the assign_attributes method if you want to bypass mass-assignment security.
class User < ActiveRecord::Base attr_protected :is_admin end user = User.new user.attributes = { :username => 'Phusion', :is_admin => true } user.username # => "Phusion" user.is_admin? # => false
# File activerecord/lib/active_record/base.rb, line 1687 def attributes=(new_attributes, guard_protected_attributes = nil) unless guard_protected_attributes.nil? message = "the use of 'guard_protected_attributes' will be removed from the next minor release of rails, " + "if you want to bypass mass-assignment security then look into using assign_attributes" ActiveSupport::Deprecation.warn(message) end return unless new_attributes.is_a?(Hash) if guard_protected_attributes == false assign_attributes(new_attributes, :without_protection => true) else assign_attributes(new_attributes) end end
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)
# File activerecord/lib/active_record/base.rb, line 1644 def cache_key case when new_record? "#{self.class.model_name.cache_key}/new" when timestamp = self[:updated_at] timestamp = timestamp.utc.to_s(:number) "#{self.class.model_name.cache_key}/#{id}-#{timestamp}" else "#{self.class.model_name.cache_key}/#{id}" end end
Returns the column object for the named attribute.
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.
Returns true if the given attribute is in the attributes 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) ]
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 1593 def init_with(coder) @attributes = coder['attributes'] @relation = nil set_serialized_attributes @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 1853 def initialize_dup(other) cloned_attributes = other.clone_attributes(:read_attribute_before_type_cast) cloned_attributes.delete(self.class.primary_key) @attributes = cloned_attributes _run_after_initialize_callbacks if respond_to?(:_run_after_initialize_callbacks) @changed_attributes = {} attributes_from_column_definition.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 clear_timestamp_attributes end
Returns the contents of the record as a nicely formatted string.
# File activerecord/lib/active_record/base.rb, line 1888 def inspect attributes_as_nice_string = self.class.column_names.collect { |name| if has_attribute?(name) "#{name}: #{attribute_for_inspect(name)}" end }.compact.join(", ") "#<#{self.class} #{attributes_as_nice_string}>" end
Marks this record as read only.
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.
Returns a String, which Action Pack uses for constructing an URL to this object. The default implementation returns this record’s id as a String, or nil if this record’s unsaved.
For example, suppose that you have a User model, and that you have a resources :users route. Normally, user_path will construct a path with the user object’s ‘id’ in it:
user = User.find_by_name('Phusion') user_path(user) # => "/users/1"
You can override to_param in your model to make user_path construct a path using the user’s name instead of the user’s id:
class User < ActiveRecord::Base def to_param # overridden name end end user = User.find_by_name('Phusion') user_path(user) # => "/users/Phusion"