class ActiveRecord::Associations::CollectionProxy
Active Record Collection Proxy
Collection proxies in Active Record are middlemen between an association
, and its target
result set.
For example, given
class Blog < ActiveRecord::Base
has_many :posts
end
blog = Blog.first
The collection proxy returned by blog.posts
is built from a :has_many
association
, and delegates to a collection of posts as the target
.
This class delegates unknown methods to the association
‘s relation class via a delegate cache.
The target
result set 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.
Inherits From
-
class
Relation
Public instance methods
Also aliased as:
push
, append
, concat
.
Adds 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 several appends may be chained together.
class Person < ActiveRecord::Base
has_many :pets
end
person.pets.size # => 0
person.pets << Pet.new(name: 'Fancy-Fancy')
person.pets << [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>
# ]
Source code GitHub
# File activerecord/lib/active_record/associations/collection_proxy.rb, line 1049
def <<(*records)
proxy_association.concat(records) && self
end
Equivalent to Array#==
. Returns true
if the two arrays contain the same number of elements and if each element is equal to the corresponding element in the other
array, otherwise returns false
.
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>
# ]
other = person.pets.to_ary
person.pets == other
# => true
Note that unpersisted records can still be seen as equal:
other = [Pet.new(id: 1), Pet.new(id: 2)]
person.pets == other
# => true
Source code GitHub
# File activerecord/lib/active_record/associations/collection_proxy.rb, line 980
def ==(other)
load_target == other
end
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 # => 1
person.pets.any? # => true
Calling it without a block when the collection is not yet loaded is equivalent to collection.exists?
. If you’re going to load the collection anyway, it is better to call collection.load.any?
to avoid an extra query.
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
Alias for:
<<
.
Also aliased as:
new
.
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
Source code GitHub
# File activerecord/lib/active_record/associations/collection_proxy.rb, line 318
def build(attributes = {}, &block)
@association.build(attributes, &block)
end
Source code GitHub
# File activerecord/lib/active_record/associations/collection_proxy.rb, line 724
def calculate(operation, column_name)
null_scope? ? scope.calculate(operation, column_name) : super
end
Equivalent to delete_all
. The difference is that returns self
, instead of an array with the deleted objects, so methods can be chained. See delete_all
for more information. Note that because delete_all
removes records by directly running an SQL query into the database, the updated_at
column of the object is not changed.
Source code GitHub
# File activerecord/lib/active_record/associations/collection_proxy.rb, line 1066
def clear
delete_all
self
end
Alias for:
<<
.
Count all records.
class Person < ActiveRecord::Base
has_many :pets
end
# This will perform the count using SQL.
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>
# ]
Passing a block will select all of a person’s pets in SQL and then perform the count using Ruby.
person.pets.count { |pet| pet.name.include?('-') } # => 2
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>
# ]
Source code GitHub
# File activerecord/lib/active_record/associations/collection_proxy.rb, line 349
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
Source code GitHub
# File activerecord/lib/active_record/associations/collection_proxy.rb, line 365
def create!(attributes = {}, &block)
@association.create!(attributes, &block)
end
Deletes the records
supplied from the collection according to the strategy specified by the :dependent
option. If no :dependent
option is given, then it will follow the default strategy. Returns an array with the deleted records.
For has_many :through
associations, the default deletion strategy is :delete_all
.
For has_many
associations, the default deletion strategy is :nullify
. This sets the foreign keys to NULL
.
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 'id': (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 Integer
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>
# ]
Source code GitHub
# File activerecord/lib/active_record/associations/collection_proxy.rb, line 620
def delete(*records)
@association.delete(*records).tap { reset_scope }
end
Deletes all the records from the collection according to the strategy specified by the :dependent
option. If no :dependent
option is given, then it will follow the default strategy.
For has_many :through
associations, the default deletion strategy is :delete_all
.
For has_many
associations, the default deletion strategy is :nullify
. This sets the foreign keys to NULL
.
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>
# ]
Both has_many
and has_many :through
dependencies default to the :delete_all
strategy if the :dependent
option is set to :destroy
. Records are not instantiated and callbacks will not be fired.
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.find(1, 2, 3)
# => ActiveRecord::RecordNotFound: Couldn't find all Pets with 'id': (1, 2, 3)
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.find(1, 2, 3)
# => ActiveRecord::RecordNotFound: Couldn't find all Pets with 'id': (1, 2, 3)
Source code GitHub
# File activerecord/lib/active_record/associations/collection_proxy.rb, line 474
def delete_all(dependent = nil)
@association.delete_all(dependent).tap { reset_scope }
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 'id': (1, 2, 3)
You can pass Integer
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 'id': (4, 5, 6)
Source code GitHub
# File activerecord/lib/active_record/associations/collection_proxy.rb, line 692
def destroy(*records)
@association.destroy(*records).tap { reset_scope }
end
Deletes the records of the collection directly from the database ignoring the :dependent
option. Records are instantiated and it invokes before_remove
, after_remove
, before_destroy
, and after_destroy
callbacks.
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
Source code GitHub
# File activerecord/lib/active_record/associations/collection_proxy.rb, line 501
def destroy_all
@association.destroy_all.tap { reset_scope }
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">]
person.pets.select(:name).distinct.distinct(false)
# => [
# #<Pet name: "Fancy-Fancy">,
# #<Pet name: "Fancy-Fancy">
# ]
Returns true
if the collection is empty. If the collection has been loaded 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.load.empty?
.
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
Source code GitHub
# File activerecord/lib/active_record/associations/collection_proxy.rb, line 831
def empty?
@association.empty?
end
Finds an object in the collection responding to the id
. Uses the same rules as ActiveRecord::FinderMethods.find
. Returns ActiveRecord::RecordNotFound
error if the object cannot 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>
# ]
Source code GitHub
# File activerecord/lib/active_record/associations/collection_proxy.rb, line 138
def find(*args)
return super if block_given?
@association.find(*args)
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) # => []
Same as first
except returns only the forty second record. Also known as accessing “the reddit”.
Returns true
if the given record
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
Source code GitHub
# File activerecord/lib/active_record/associations/collection_proxy.rb, line 927
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) # => []
Source code GitHub
# File activerecord/lib/active_record/associations/collection_proxy.rb, line 259
def last(limit = nil)
load_target if find_from_target?
super
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>
# ]
Source code GitHub
# File activerecord/lib/active_record/associations/collection_proxy.rb, line 44
def load_target
@association.load_target
end
Alias for:
loaded?
.
Also aliased as:
loaded
.
Returns true
if the association has been loaded, otherwise false
.
person.pets.loaded? # => false
person.pets.records
person.pets.loaded? # => true
Source code GitHub
# File activerecord/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
Alias for:
build
.
Source code GitHub
# File activerecord/lib/active_record/associations/collection_proxy.rb, line 728
def pluck(*column_names)
null_scope? ? scope.pluck(*column_names) : super
end
Returns the association object for the collection.
class Person < ActiveRecord::Base
has_many :pets
end
person.pets.proxy_association
# => #<ActiveRecord::Associations::HasManyAssociation owner="#<Person:0x00>">
Returns the same object as person.association(:pets)
, allowing you to make calls like person.pets.proxy_association.owner
.
See Association extensions at Associations::ClassMethods
for more.
Source code GitHub
# File activerecord/lib/active_record/associations/collection_proxy.rb, line 944
def proxy_association
@association
end
Alias for:
<<
.
Reloads the collection from the database. Returns self
.
class Person < ActiveRecord::Base
has_many :pets
end
person.pets # fetches pets from the database
# => [#<Pet id: 1, name: "Snoop", group: "dogs", person_id: 1>]
person.pets # uses the pets cache
# => [#<Pet id: 1, name: "Snoop", group: "dogs", person_id: 1>]
person.pets.reload # fetches pets from the database
# => [#<Pet id: 1, name: "Snoop", group: "dogs", person_id: 1>]
Source code GitHub
# File activerecord/lib/active_record/associations/collection_proxy.rb, line 1085
def reload
proxy_association.reload(true)
reset_scope
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
Source code GitHub
# File activerecord/lib/active_record/associations/collection_proxy.rb, line 391
def replace(other_array)
@association.replace(other_array)
end
Unloads the association. Returns self
.
class Person < ActiveRecord::Base
has_many :pets
end
person.pets # fetches pets from the database
# => [#<Pet id: 1, name: "Snoop", group: "dogs", person_id: 1>]
person.pets # uses the pets cache
# => [#<Pet id: 1, name: "Snoop", group: "dogs", person_id: 1>]
person.pets.reset # clears the pets cache
person.pets # fetches pets from the database
# => [#<Pet id: 1, name: "Snoop", group: "dogs", person_id: 1>]
Source code GitHub
# File activerecord/lib/active_record/associations/collection_proxy.rb, line 1106
def reset
proxy_association.reset
proxy_association.reset_scope
reset_scope
end
Returns a Relation object for the records in this association
Source code GitHub
# File activerecord/lib/active_record/associations/collection_proxy.rb, line 949
def scope
@scope ||= @association.scope
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 except id
that is not in the initialized record you’ll receive:
person.pets.select(:name).first.person_id
# => ActiveModel::MissingAttributeError: missing attribute 'person_id' for Pet
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| /oo/.match?(pet.name) }
# => [
# #<Pet id: 2, name: "Spook", person_id: 1>,
# #<Pet id: 3, name: "Choo-Choo", person_id: 1>
# ]
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.
Source code GitHub
# File activerecord/lib/active_record/associations/collection_proxy.rb, line 782
def size
@association.size
end
Gives a record (or N records if a parameter is supplied) from the collection using the same rules as ActiveRecord::FinderMethods.take
.
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.take # => #<Pet id: 1, name: "Fancy-Fancy", person_id: 1>
person.pets.take(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.take # => nil
another_person_without.pets.take(2) # => []
Source code GitHub
# File activerecord/lib/active_record/associations/collection_proxy.rb, line 289
def take(limit = nil)
load_target if find_from_target?
super
end
Source code GitHub
# File activerecord/lib/active_record/associations/collection_proxy.rb, line 40
def target
@association.target
end