Association proxies in Active Record are
middlemen between the object that holds the association, known as the
@owner
, and the actual associated object, known as the
@target
. The kind of association any proxy is about is
available in @reflection
. That's an instance of the class
ActiveRecord::Reflection::AssociationReflection.
For example, given
class Blog < ActiveRecord::Base has_many :posts end blog = Blog.first
the association proxy in blog.posts
has the object in
blog
as @owner
, the collection of its posts as
@target
, and the @reflection
object represents a
:has_many
macro.
This class delegates unknown methods to @target
via
method_missing
.
The @target
object is not loaded until needed. For example,
blog.posts.count
is computed directly through SQL and does not trigger by itself the instantiation of the actual post records.
Returns true
if the collection is not empty.
class Person < ActiveRecord::Base has_many :pets end person.pets.count # => 0 person.pets.any? # => false person.pets << Pet.new(name: 'Snoop') person.pets.count # => 0 person.pets.any? # => true
You can also pass a block to define criteria. The behavior is the same, it returns true if the collection based on the criteria is not empty.
person.pets # => [#<Pet name: "Snoop", group: "dogs">] person.pets.any? do |pet| pet.group == 'cats' end # => false person.pets.any? do |pet| pet.group == 'dogs' end # => true
# File lib/active_record/associations/collection_proxy.rb, line 780 def any?(&block) @association.any?(&block) end
Returns a new object of the collection type that has been instantiated with
attributes
and linked to this object, but have not yet been
saved. You can pass an array of attributes hashes, this will return an
array with the new objects.
class Person has_many :pets end person.pets.build # => #<Pet id: nil, name: nil, person_id: 1> person.pets.build(name: 'Fancy-Fancy') # => #<Pet id: nil, name: "Fancy-Fancy", person_id: 1> person.pets.build([{name: 'Spook'}, {name: 'Choo-Choo'}, {name: 'Brain'}]) # => [ # #<Pet id: nil, name: "Spook", person_id: 1>, # #<Pet id: nil, name: "Choo-Choo", person_id: 1>, # #<Pet id: nil, name: "Brain", person_id: 1> # ] person.pets.size # => 5 # size of the collection person.pets.count # => 0 # count from database
# File lib/active_record/associations/collection_proxy.rb, line 228 def build(attributes = {}, &block) @association.build(attributes, &block) end
Add one or more records to the collection by setting their foreign keys to
the association's primary key. Since << flattens its argument
list and inserts each record, push
and concat
behave identically. Returns self
so method calls may be
chained.
class Person < ActiveRecord::Base pets :has_many end person.pets.size # => 0 person.pets.concat(Pet.new(name: 'Fancy-Fancy')) person.pets.concat(Pet.new(name: 'Spook'), Pet.new(name: 'Choo-Choo')) person.pets.size # => 3 person.id # => 1 person.pets # => [ # #<Pet id: 1, name: "Fancy-Fancy", person_id: 1>, # #<Pet id: 2, name: "Spook", person_id: 1>, # #<Pet id: 3, name: "Choo-Choo", person_id: 1> # ] person.pets.concat([Pet.new(name: 'Brain'), Pet.new(name: 'Benny')]) person.pets.size # => 5
# File lib/active_record/associations/collection_proxy.rb, line 303 def concat(*records) @association.concat(*records) end
Count all records using SQL.
class Person < ActiveRecord::Base has_many :pets end person.pets.count # => 3 person.pets # => [ # #<Pet id: 1, name: "Fancy-Fancy", person_id: 1>, # #<Pet id: 2, name: "Spook", person_id: 1>, # #<Pet id: 3, name: "Choo-Choo", person_id: 1> # ]
# File lib/active_record/associations/collection_proxy.rb, line 673 def count(column_name = nil, options = {}) @association.count(column_name, options) end
Returns a new object of the collection type that has been instantiated with attributes, linked to this object and that has already been saved (if it passes the validations).
class Person has_many :pets end person.pets.create(name: 'Fancy-Fancy') # => #<Pet id: 1, name: "Fancy-Fancy", person_id: 1> person.pets.create([{name: 'Spook'}, {name: 'Choo-Choo'}]) # => [ # #<Pet id: 2, name: "Spook", person_id: 1>, # #<Pet id: 3, name: "Choo-Choo", person_id: 1> # ] person.pets.size # => 3 person.pets.count # => 3 person.pets.find(1, 2, 3) # => [ # #<Pet id: 1, name: "Fancy-Fancy", person_id: 1>, # #<Pet id: 2, name: "Spook", person_id: 1>, # #<Pet id: 3, name: "Choo-Choo", person_id: 1> # ]
# File lib/active_record/associations/collection_proxy.rb, line 259 def create(attributes = {}, &block) @association.create(attributes, &block) end
Like create
, except that if the record is invalid, raises an
exception.
class Person has_many :pets end class Pet validates :name, presence: true end person.pets.create!(name: nil) # => ActiveRecord::RecordInvalid: Validation failed: Name can't be blank
# File lib/active_record/associations/collection_proxy.rb, line 275 def create!(attributes = {}, &block) @association.create!(attributes, &block) end
Deletes the records
supplied and removes them from the
collection. For has_many
associations, the deletion is done
according to the strategy specified by the :dependent
option.
Returns an array with the deleted records.
If no :dependent
option is given, then it will follow the
default strategy. The default strategy is :nullify
. This sets
the foreign keys to NULL
. For, has_many
:through
, the default strategy is delete_all
.
class Person < ActiveRecord::Base has_many :pets # dependent: :nullify option by default end person.pets.size # => 3 person.pets # => [ # #<Pet id: 1, name: "Fancy-Fancy", person_id: 1>, # #<Pet id: 2, name: "Spook", person_id: 1>, # #<Pet id: 3, name: "Choo-Choo", person_id: 1> # ] person.pets.delete(Pet.find(1)) # => [#<Pet id: 1, name: "Fancy-Fancy", person_id: 1>] person.pets.size # => 2 person.pets # => [ # #<Pet id: 2, name: "Spook", person_id: 1>, # #<Pet id: 3, name: "Choo-Choo", person_id: 1> # ] Pet.find(1) # => #<Pet id: 1, name: "Fancy-Fancy", person_id: nil>
If it is set to :destroy
all the records
are
removed by calling their destroy
method. See
destroy
for more information.
class Person < ActiveRecord::Base has_many :pets, dependent: :destroy end person.pets.size # => 3 person.pets # => [ # #<Pet id: 1, name: "Fancy-Fancy", person_id: 1>, # #<Pet id: 2, name: "Spook", person_id: 1>, # #<Pet id: 3, name: "Choo-Choo", person_id: 1> # ] person.pets.delete(Pet.find(1), Pet.find(3)) # => [ # #<Pet id: 1, name: "Fancy-Fancy", person_id: 1>, # #<Pet id: 3, name: "Choo-Choo", person_id: 1> # ] person.pets.size # => 1 person.pets # => [#<Pet id: 2, name: "Spook", person_id: 1>] Pet.find(1, 3) # => ActiveRecord::RecordNotFound: Couldn't find all Pets with IDs (1, 3)
If it is set to :delete_all
, all the records
are
deleted without calling their destroy
method.
class Person < ActiveRecord::Base has_many :pets, dependent: :delete_all end person.pets.size # => 3 person.pets # => [ # #<Pet id: 1, name: "Fancy-Fancy", person_id: 1>, # #<Pet id: 2, name: "Spook", person_id: 1>, # #<Pet id: 3, name: "Choo-Choo", person_id: 1> # ] person.pets.delete(Pet.find(1)) # => [#<Pet id: 1, name: "Fancy-Fancy", person_id: 1>] person.pets.size # => 2 person.pets # => [ # #<Pet id: 2, name: "Spook", person_id: 1>, # #<Pet id: 3, name: "Choo-Choo", person_id: 1> # ] Pet.find(1) # => ActiveRecord::RecordNotFound: Couldn't find Pet with id=1
You can pass Fixnum
or String
values, it finds
the records responding to the id
and executes delete on them.
class Person < ActiveRecord::Base has_many :pets end person.pets.size # => 3 person.pets # => [ # #<Pet id: 1, name: "Fancy-Fancy", person_id: 1>, # #<Pet id: 2, name: "Spook", person_id: 1>, # #<Pet id: 3, name: "Choo-Choo", person_id: 1> # ] person.pets.delete("1") # => [#<Pet id: 1, name: "Fancy-Fancy", person_id: 1>] person.pets.delete(2, 3) # => [ # #<Pet id: 2, name: "Spook", person_id: 1>, # #<Pet id: 3, name: "Choo-Choo", person_id: 1> # ]
# File lib/active_record/associations/collection_proxy.rb, line 565 def delete(*records) @association.delete(*records) end
Deletes all the records from the collection. For has_many
associations, the deletion is done according to the strategy specified by
the :dependent
option. Returns an array with the deleted
records.
If no :dependent
option is given, then it will follow the
default strategy. The default strategy is :nullify
. This sets
the foreign keys to NULL
. For, has_many
:through
, the default strategy is delete_all
.
class Person < ActiveRecord::Base has_many :pets # dependent: :nullify option by default end person.pets.size # => 3 person.pets # => [ # #<Pet id: 1, name: "Fancy-Fancy", person_id: 1>, # #<Pet id: 2, name: "Spook", person_id: 1>, # #<Pet id: 3, name: "Choo-Choo", person_id: 1> # ] person.pets.delete_all # => [ # #<Pet id: 1, name: "Fancy-Fancy", person_id: 1>, # #<Pet id: 2, name: "Spook", person_id: 1>, # #<Pet id: 3, name: "Choo-Choo", person_id: 1> # ] person.pets.size # => 0 person.pets # => [] Pet.find(1, 2, 3) # => [ # #<Pet id: 1, name: "Fancy-Fancy", person_id: nil>, # #<Pet id: 2, name: "Spook", person_id: nil>, # #<Pet id: 3, name: "Choo-Choo", person_id: nil> # ]
If it is set to :destroy
all the objects from the collection
are removed by calling their destroy
method. See
destroy
for more information.
class Person < ActiveRecord::Base has_many :pets, dependent: :destroy end person.pets.size # => 3 person.pets # => [ # #<Pet id: 1, name: "Fancy-Fancy", person_id: 1>, # #<Pet id: 2, name: "Spook", person_id: 1>, # #<Pet id: 3, name: "Choo-Choo", person_id: 1> # ] person.pets.delete_all # => [ # #<Pet id: 1, name: "Fancy-Fancy", person_id: 1>, # #<Pet id: 2, name: "Spook", person_id: 1>, # #<Pet id: 3, name: "Choo-Choo", person_id: 1> # ] Pet.find(1, 2, 3) # => ActiveRecord::RecordNotFound
If it is set to :delete_all
, all the objects are deleted
without calling their destroy
method.
class Person < ActiveRecord::Base has_many :pets, dependent: :delete_all end person.pets.size # => 3 person.pets # => [ # #<Pet id: 1, name: "Fancy-Fancy", person_id: 1>, # #<Pet id: 2, name: "Spook", person_id: 1>, # #<Pet id: 3, name: "Choo-Choo", person_id: 1> # ] person.pets.delete_all # => [ # #<Pet id: 1, name: "Fancy-Fancy", person_id: 1>, # #<Pet id: 2, name: "Spook", person_id: 1>, # #<Pet id: 3, name: "Choo-Choo", person_id: 1> # ] Pet.find(1, 2, 3) # => ActiveRecord::RecordNotFound
# File lib/active_record/associations/collection_proxy.rb, line 421 def delete_all @association.delete_all end
Destroys the records
supplied and removes them from the
collection. This method will always remove record from the
database ignoring the :dependent
option. Returns an array with
the removed records.
class Person < ActiveRecord::Base has_many :pets end person.pets.size # => 3 person.pets # => [ # #<Pet id: 1, name: "Fancy-Fancy", person_id: 1>, # #<Pet id: 2, name: "Spook", person_id: 1>, # #<Pet id: 3, name: "Choo-Choo", person_id: 1> # ] person.pets.destroy(Pet.find(1)) # => [#<Pet id: 1, name: "Fancy-Fancy", person_id: 1>] person.pets.size # => 2 person.pets # => [ # #<Pet id: 2, name: "Spook", person_id: 1>, # #<Pet id: 3, name: "Choo-Choo", person_id: 1> # ] person.pets.destroy(Pet.find(2), Pet.find(3)) # => [ # #<Pet id: 2, name: "Spook", person_id: 1>, # #<Pet id: 3, name: "Choo-Choo", person_id: 1> # ] person.pets.size # => 0 person.pets # => [] Pet.find(1, 2, 3) # => ActiveRecord::RecordNotFound: Couldn't find all Pets with IDs (1, 2, 3)
You can pass Fixnum
or String
values, it finds
the records responding to the id
and then deletes them from
the database.
person.pets.size # => 3 person.pets # => [ # #<Pet id: 4, name: "Benny", person_id: 1>, # #<Pet id: 5, name: "Brain", person_id: 1>, # #<Pet id: 6, name: "Boss", person_id: 1> # ] person.pets.destroy("4") # => #<Pet id: 4, name: "Benny", person_id: 1> person.pets.size # => 2 person.pets # => [ # #<Pet id: 5, name: "Brain", person_id: 1>, # #<Pet id: 6, name: "Boss", person_id: 1> # ] person.pets.destroy(5, 6) # => [ # #<Pet id: 5, name: "Brain", person_id: 1>, # #<Pet id: 6, name: "Boss", person_id: 1> # ] person.pets.size # => 0 person.pets # => [] Pet.find(4, 5, 6) # => ActiveRecord::RecordNotFound: Couldn't find all Pets with IDs (4, 5, 6)
# File lib/active_record/associations/collection_proxy.rb, line 637 def destroy(*records) @association.destroy(*records) end
Deletes the records of the collection directly from the database. This will
always remove the records ignoring the :dependent
option.
class Person < ActiveRecord::Base has_many :pets end person.pets.size # => 3 person.pets # => [ # #<Pet id: 1, name: "Fancy-Fancy", person_id: 1>, # #<Pet id: 2, name: "Spook", person_id: 1>, # #<Pet id: 3, name: "Choo-Choo", person_id: 1> # ] person.pets.destroy_all person.pets.size # => 0 person.pets # => [] Pet.find(1) # => Couldn't find Pet with id=1
# File lib/active_record/associations/collection_proxy.rb, line 447 def destroy_all @association.destroy_all end
Specifies whether the records should be unique or not.
class Person < ActiveRecord::Base has_many :pets end person.pets.select(:name) # => [ # #<Pet name: "Fancy-Fancy">, # #<Pet name: "Fancy-Fancy"> # ] person.pets.select(:name).distinct # => [#<Pet name: "Fancy-Fancy">]
# File lib/active_record/associations/collection_proxy.rb, line 655 def distinct @association.distinct end
Returns true
if the collection is empty. If the collection has
been loaded or the :counter_sql
option is provided, it is
equivalent to collection.size.zero?
. If the collection has not
been loaded, it is equivalent to collection.exists?
. If the
collection has not already been loaded and you are going to fetch the
records anyway it is better to check collection.length.zero?
.
class Person < ActiveRecord::Base has_many :pets end person.pets.count # => 1 person.pets.empty? # => false person.pets.delete_all person.pets.count # => 0 person.pets.empty? # => true
# File lib/active_record/associations/collection_proxy.rb, line 747 def empty? @association.empty? end
Finds an object in the collection responding to the id
. Uses
the same rules as ActiveRecord::Base.find
. Returns
ActiveRecord::RecordNotFound
error if the object can not be
found.
class Person < ActiveRecord::Base has_many :pets end person.pets # => [ # #<Pet id: 1, name: "Fancy-Fancy", person_id: 1>, # #<Pet id: 2, name: "Spook", person_id: 1>, # #<Pet id: 3, name: "Choo-Choo", person_id: 1> # ] person.pets.find(1) # => #<Pet id: 1, name: "Fancy-Fancy", person_id: 1> person.pets.find(4) # => ActiveRecord::RecordNotFound: Couldn't find Pet with id=4 person.pets.find(2) { |pet| pet.name.downcase! } # => #<Pet id: 2, name: "fancy-fancy", person_id: 1> person.pets.find(2, 3) # => [ # #<Pet id: 2, name: "Spook", person_id: 1>, # #<Pet id: 3, name: "Choo-Choo", person_id: 1> # ]
# File lib/active_record/associations/collection_proxy.rb, line 140 def find(*args, &block) @association.find(*args, &block) end
Returns the first record, or the first n
records, from the
collection. If the collection is empty, the first form returns
nil
, and the second form returns an empty array.
class Person < ActiveRecord::Base has_many :pets end person.pets # => [ # #<Pet id: 1, name: "Fancy-Fancy", person_id: 1>, # #<Pet id: 2, name: "Spook", person_id: 1>, # #<Pet id: 3, name: "Choo-Choo", person_id: 1> # ] person.pets.first # => #<Pet id: 1, name: "Fancy-Fancy", person_id: 1> person.pets.first(2) # => [ # #<Pet id: 1, name: "Fancy-Fancy", person_id: 1>, # #<Pet id: 2, name: "Spook", person_id: 1> # ] another_person_without.pets # => [] another_person_without.pets.first # => nil another_person_without.pets.first(3) # => []
# File lib/active_record/associations/collection_proxy.rb, line 170 def first(*args) @association.first(*args) end
Returns true
if the given object is present in the collection.
class Person < ActiveRecord::Base has_many :pets end person.pets # => [#<Pet id: 20, name: "Snoop">] person.pets.include?(Pet.find(20)) # => true person.pets.include?(Pet.find(21)) # => false
# File lib/active_record/associations/collection_proxy.rb, line 832 def include?(record) !!@association.include?(record) end
Returns the last record, or the last n
records, from the
collection. If the collection is empty, the first form returns
nil
, and the second form returns an empty array.
class Person < ActiveRecord::Base has_many :pets end person.pets # => [ # #<Pet id: 1, name: "Fancy-Fancy", person_id: 1>, # #<Pet id: 2, name: "Spook", person_id: 1>, # #<Pet id: 3, name: "Choo-Choo", person_id: 1> # ] person.pets.last # => #<Pet id: 3, name: "Choo-Choo", person_id: 1> person.pets.last(2) # => [ # #<Pet id: 2, name: "Spook", person_id: 1>, # #<Pet id: 3, name: "Choo-Choo", person_id: 1> # ] another_person_without.pets # => [] another_person_without.pets.last # => nil another_person_without.pets.last(3) # => []
# File lib/active_record/associations/collection_proxy.rb, line 200 def last(*args) @association.last(*args) end
Returns the size of the collection calling size
on the target.
If the collection has been already loaded, length
and
size
are equivalent. If not and you are going to need the
records anyway this method will take one less query. Otherwise
size
is more efficient.
class Person < ActiveRecord::Base has_many :pets end person.pets.length # => 3 # executes something like SELECT "pets".* FROM "pets" WHERE "pets"."person_id" = 1 # Because the collection is loaded, you can # call the collection with no additional queries: person.pets # => [ # #<Pet id: 1, name: "Fancy-Fancy", person_id: 1>, # #<Pet id: 2, name: "Spook", person_id: 1>, # #<Pet id: 3, name: "Choo-Choo", person_id: 1> # ]
# File lib/active_record/associations/collection_proxy.rb, line 725 def length @association.length end
# File lib/active_record/associations/collection_proxy.rb, line 44 def load_target @association.load_target end
Returns true
if the association has been loaded, otherwise
false
.
person.pets.loaded? # => false person.pets person.pets.loaded? # => true
# File lib/active_record/associations/collection_proxy.rb, line 53 def loaded? @association.loaded? end
Returns true if the collection has more than one record. Equivalent to
collection.size > 1
.
class Person < ActiveRecord::Base has_many :pets end person.pets.count #=> 1 person.pets.many? #=> false person.pets << Pet.new(name: 'Snoopy') person.pets.count #=> 2 person.pets.many? #=> true
You can also pass a block to define criteria. The behavior is the same, it returns true if the collection based on the criteria has more than one record.
person.pets # => [ # #<Pet name: "Gorby", group: "cats">, # #<Pet name: "Puff", group: "cats">, # #<Pet name: "Snoop", group: "dogs"> # ] person.pets.many? do |pet| pet.group == 'dogs' end # => false person.pets.many? do |pet| pet.group == 'cats' end # => true
# File lib/active_record/associations/collection_proxy.rb, line 818 def many?(&block) @association.many?(&block) end
# File lib/active_record/associations/collection_proxy.rb, line 836 def proxy_association @association end
Replaces this collection with other_array
. This will perform a
diff and delete/add only records that have changed.
class Person < ActiveRecord::Base has_many :pets end person.pets # => [#<Pet id: 1, name: "Gorby", group: "cats", person_id: 1>] other_pets = [Pet.new(name: 'Puff', group: 'celebrities'] person.pets.replace(other_pets) person.pets # => [#<Pet id: 2, name: "Puff", group: "celebrities", person_id: 1>]
If the supplied array has an incorrect association type, it raises an
ActiveRecord::AssociationTypeMismatch
error:
person.pets.replace(["doo", "ggie", "gaga"]) # => ActiveRecord::AssociationTypeMismatch: Pet expected, got String
# File lib/active_record/associations/collection_proxy.rb, line 329 def replace(other_array) @association.replace(other_array) end
Returns a Relation
object for the records in this association
# File lib/active_record/associations/collection_proxy.rb, line 849 def scope @association.scope end
We don't want this object to be put on the scoping stack, because that could create an infinite loop where we call an @association method, which gets the current scope, which is this object, which delegates to @association, and so on.
# File lib/active_record/associations/collection_proxy.rb, line 844 def scoping @association.scope.scoping { yield } end
Works in two ways.
First: Specify a subset of fields to be selected from the result set.
class Person < ActiveRecord::Base has_many :pets end person.pets # => [ # #<Pet id: 1, name: "Fancy-Fancy", person_id: 1>, # #<Pet id: 2, name: "Spook", person_id: 1>, # #<Pet id: 3, name: "Choo-Choo", person_id: 1> # ] person.pets.select(:name) # => [ # #<Pet id: nil, name: "Fancy-Fancy">, # #<Pet id: nil, name: "Spook">, # #<Pet id: nil, name: "Choo-Choo"> # ] person.pets.select([:id, :name]) # => [ # #<Pet id: 1, name: "Fancy-Fancy">, # #<Pet id: 2, name: "Spook">, # #<Pet id: 3, name: "Choo-Choo"> # ]
Be careful because this also means you're initializing a model object with only the fields that you've selected. If you attempt to access a field that is not in the initialized record you'll receive:
person.pets.select(:name).first.person_id # => ActiveModel::MissingAttributeError: missing attribute: person_id
Second: You can pass a block so it can be used just like Array#select. This builds an array of objects from the database for the scope, converting them into an array and iterating through them using Array#select.
person.pets.select { |pet| pet.name =~ /oo/ } # => [ # #<Pet id: 2, name: "Spook", person_id: 1>, # #<Pet id: 3, name: "Choo-Choo", person_id: 1> # ] person.pets.select(:name) { |pet| pet.name =~ /oo/ } # => [ # #<Pet id: 2, name: "Spook">, # #<Pet id: 3, name: "Choo-Choo"> # ]
# File lib/active_record/associations/collection_proxy.rb, line 110 def select(select = nil, &block) @association.select(select, &block) end
Returns the size of the collection. If the collection hasn't been
loaded, it executes a SELECT COUNT(*)
query. Else it calls
collection.size
.
If the collection has been already loaded size
and
length
are equivalent. If not and you are going to need the
records anyway length
will take one less query. Otherwise
size
is more efficient.
class Person < ActiveRecord::Base has_many :pets end person.pets.size # => 3 # executes something like SELECT COUNT(*) FROM "pets" WHERE "pets"."person_id" = 1 person.pets # This will execute a SELECT * FROM query # => [ # #<Pet id: 1, name: "Fancy-Fancy", person_id: 1>, # #<Pet id: 2, name: "Spook", person_id: 1>, # #<Pet id: 3, name: "Choo-Choo", person_id: 1> # ] person.pets.size # => 3 # Because the collection is already loaded, this will behave like # collection.size and no SQL count query is executed.
# File lib/active_record/associations/collection_proxy.rb, line 701 def size @association.size end
# File lib/active_record/associations/collection_proxy.rb, line 40 def target @association.target end