Active Record objects don‘t specify their attributes directly, but rather infer them from the table definition with which they‘re linked. Adding, removing, and changing attributes and their type is done directly in the database. Any change is instantly reflected in the Active Record objects. The mapping that binds a given Active Record class to a certain database table will happen automatically in most common cases, but can be overwritten for the uncommon ones.
See the mapping rules in table_name and the full example in files/activerecord/README_rdoc.html for more insight.
Active Records accept constructor parameters either in a hash or as a block. The hash method is especially useful when you‘re receiving the data from somewhere else, like an HTTP request. It works like this:
user = User.new(:name => "David", :occupation => "Code Artist") user.name # => "David"
You can also use block initialization:
user = User.new do |u| u.name = "David" u.occupation = "Code Artist" end
And of course you can just create a bare object and specify the attributes after the fact:
user = User.new user.name = "David" user.occupation = "Code Artist"
Conditions can either be specified as a string, array, or hash representing the WHERE-part of an SQL statement. The array form is to be used when the condition input is tainted and requires sanitization. The string form can be used for statements that don‘t involve tainted data. The hash form works much like the array form, except only equality and range is possible. Examples:
class User < ActiveRecord::Base def self.authenticate_unsafely(user_name, password) where("user_name = '#{user_name}' AND password = '#{password}'").first end def self.authenticate_safely(user_name, password) where("user_name = ? AND password = ?", user_name, password).first end def self.authenticate_safely_simply(user_name, password) where(:user_name => user_name, :password => password).first end end
The authenticate_unsafely method inserts the parameters directly into the query and is thus susceptible to SQL-injection attacks if the user_name and password parameters come directly from an HTTP request. The authenticate_safely and authenticate_safely_simply both will sanitize the user_name and password before inserting them in the query, which will ensure that an attacker can‘t escape the query and fake the login (or worse).
When using multiple parameters in the conditions, it can easily become hard to read exactly what the fourth or fifth question mark is supposed to represent. In those cases, you can resort to named bind variables instead. That‘s done by replacing the question marks with symbols and supplying a hash with values for the matching symbol keys:
Company.where( "id = :id AND name = :name AND division = :division AND created_at > :accounting_date", { :id => 3, :name => "37signals", :division => "First", :accounting_date => '2005-01-01' } ).first
Similarly, a simple hash without a statement will generate conditions based on equality with the SQL AND operator. For instance:
Student.where(:first_name => "Harvey", :status => 1) Student.where(params[:student])
A range may be used in the hash to use the SQL BETWEEN operator:
Student.where(:grade => 9..12)
An array may be used in the hash to use the SQL IN operator:
Student.where(:grade => [9,11,12])
When joining tables, nested hashes or keys written in the form ‘table_name.column_name’ can be used to qualify the table name of a particular condition. For instance:
Student.joins(:schools).where(:schools => { :type => 'public' }) Student.joins(:schools).where('schools.type' => 'public' )
All column values are automatically available through basic accessors on the Active Record object, but sometimes you want to specialize this behavior. This can be done by overwriting the default accessors (using the same name as the attribute) and calling read_attribute(attr_name) and write_attribute(attr_name, value) to actually change things.
class Song < ActiveRecord::Base # Uses an integer of seconds to hold the length of the song def length=(minutes) write_attribute(:length, minutes.to_i * 60) end def length read_attribute(:length) / 60 end end
You can alternatively use self[:attribute]=(value) and self[:attribute] instead of write_attribute(:attribute, value) and read_attribute(:attribute).
In addition to the basic accessors, query methods are also automatically available on the Active Record object. Query methods allow you to test whether an attribute value is present.
For example, an Active Record User with the name attribute has a name? method that you can call to determine whether the user has a name:
user = User.new(:name => "David") user.name? # => true anonymous = User.new(:name => "") anonymous.name? # => false
Sometimes you want to be able to read the raw attribute data without having the column-determined typecast run its course first. That can be done by using the <attribute>_before_type_cast accessors that all attributes have. For example, if your Account model has a balance attribute, you can call account.balance_before_type_cast or account.id_before_type_cast.
This is especially useful in validation situations where the user might supply a string for an integer field and you want to display the original string back in an error message. Accessing the attribute normally would typecast the string to 0, which isn‘t what you want.
Dynamic attribute-based finders are a cleaner way of getting (and/or creating) objects by simple queries without turning to SQL. They work by appending the name of an attribute to find_by_, find_last_by_, or find_all_by_ and thus produces finders like Person.find_by_user_name, Person.find_all_by_last_name, and Payment.find_by_transaction_id. Instead of writing Person.where(:user_name => user_name).first, you just do Person.find_by_user_name(user_name). And instead of writing Person.where(:last_name => last_name).all, you just do Person.find_all_by_last_name(last_name).
It‘s 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 #with dynamic finder Person.where(:user_name => user_name, :password => password, :gender => 'male').first Payment.find_by_user_name_and_password_and_gender
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')
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
Active Record allows inheritance by storing the name of the class in a column that by default is named "type" (can be changed by overwriting Base.inheritance_column). This means that an inheritance looking like this:
class Company < ActiveRecord::Base; end class Firm < Company; end class Client < Company; end class PriorityClient < Client; end
When you do Firm.create(:name => "37signals"), this record will be saved in the companies table with type = "Firm". You can then fetch this row again using Company.where(:name => ‘37signals’).first and it will return a Firm object.
If you don‘t have a type column defined in your table, single-table inheritance won‘t be triggered. In that case, it‘ll work just like normal subclasses with no special magic for differentiating between them or reloading the right type with find.
Note, all the attributes for all the cases are kept in the same table. Read more: www.martinfowler.com/eaaCatalog/singleTableInheritance.html
Connections are usually created through ActiveRecord::Base.establish_connection and retrieved by ActiveRecord::Base.connection. All classes inheriting from ActiveRecord::Base will use this connection. But you can also set a class-specific connection. For example, if Course is an ActiveRecord::Base, but resides in a different database, you can just say Course.establish_connection and Course and all of its subclasses will use this connection instead.
This feature is implemented by keeping a connection pool in ActiveRecord::Base that is a Hash indexed by the class. If a connection is requested, the retrieve_connection method will go up the class-hierarchy until a connection is found in the connection pool.
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.
colorize_logging | -> | colorize_logging= |
set_table_name | -> | table_name= |
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 |
abstract_class | [RW] | Set this to true if this is an abstract class (see abstract_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.
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 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 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.
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 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
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.
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.
# 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"}>, ...]
Defines the column name for use with single table inheritance. Use set_inheritance_column to set a different value.
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.
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
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.
# Serialize a preferences attribute class User serialize :preferences end
Returns a hash of all the attributes that have been specified for serialization as keys and their class restriction as values.
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
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.
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
Returns the class descending directly from ActiveRecord::Base or an abstract class, if any, in the inheritance hierarchy.
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.
Sets the default options for the model. The format of the options argument is the same as in find.
class Person < ActiveRecord::Base default_scope order('last_name, first_name') end
default_scope is also applied while creating/building a record. It is not applied while updating a record.
class Article < ActiveRecord::Base default_scope where(:published => true) end Article.new.published # => true Article.create.published # => true
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" }
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'"
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'"
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'"
Works like with_scope, but discards any nested properties.
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.
Returns true if comparison_object is the same exact object, or comparison_object is of the same type and self has an ID and it is equal to +comparison_object.id+.
Note that new records are different from any other record by definition, unless the other record is the receiver itself. Besides, if you fetch existing records with select and leave the ID out, you‘re on your own, this predicate will return false.
Note also that destroying a record preserves its ID in the model instance, so deleted models are still comparable.
Returns the 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).
Updates the attribute identified by attr_name with the specified value. (Alias for the protected write_attribute method).
Returns an inspect-like string for the value of the attribute attr_name. String attributes are elided after 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"'
Returns an array of names for the attributes available on this object sorted alphabetically.
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 guard_protected_attributes is true (the default), then 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.
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 user.send(:attributes=, { :username => 'Phusion', :is_admin => true }, false) user.is_admin? # => true
Returns a cache key that can be used to identify this record.
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)
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.
Freeze the attributes hash such that associations are still accessible, even on destroyed records.
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'
Cloned objects have no id assigned and are treated as new records. Note that this is a "shallow" clone as 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.
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"