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.
- #
- A
- B
- C
- D
- E
- F
- I
- L
- M
- N
- P
- R
- S
- T
Instance Public methods
<<(*records) Link
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>
# ]
==(other) Link
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
other = [Pet.new(id: 1), Pet.new(id: 2)]
person.pets == other
# => false
any?() Link
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
Source: on GitHub
# File activerecord/lib/active_record/associations/collection_proxy.rb, line 834
build(attributes = {}, &block) Link
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
calculate(operation, column_name) Link
clear() Link
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.
count(column_name = nil, &block) Link
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
Source: on GitHub
# File activerecord/lib/active_record/associations/collection_proxy.rb, line 731
create(attributes = {}, &block) Link
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>
# ]
create!(attributes = {}, &block) Link
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
delete(*records) Link
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>
# ]
delete_all(dependent = nil) Link
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)
destroy(*records) Link
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)
destroy_all() Link
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
distinct(value = true) Link
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">
# ]
Source: on GitHub
# File activerecord/lib/active_record/associations/collection_proxy.rb, line 695
empty?() Link
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
fifth() Link
Same as first
except returns only the fifth record.
Source: on GitHub
# File activerecord/lib/active_record/associations/collection_proxy.rb, line 199
find(*args) Link
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 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>
# ]
first(limit = nil) Link
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) # => []
Source: on GitHub
# File activerecord/lib/active_record/associations/collection_proxy.rb, line 142
forty_two() Link
Same as first
except returns only the forty second record. Also known as accessing “the reddit”.
Source: on GitHub
# File activerecord/lib/active_record/associations/collection_proxy.rb, line 207
fourth() Link
Same as first
except returns only the fourth record.
Source: on GitHub
# File activerecord/lib/active_record/associations/collection_proxy.rb, line 191
include?(record) Link
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
last(limit = nil) Link
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) # => []
length() Link
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: on GitHub
# File activerecord/lib/active_record/associations/collection_proxy.rb, line 785
load_target() Link
loaded?() Link
Returns true
if the association has been loaded, otherwise false
.
person.pets.loaded? # => false
person.pets.records
person.pets.loaded? # => true
many?() Link
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
Source: on GitHub
# File activerecord/lib/active_record/associations/collection_proxy.rb, line 875
pluck(*column_names) Link
reload() Link
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>]
replace(other_array) Link
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
reset() Link
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>]
scope() Link
Returns a Relation
object for the records in this association
second() Link
Same as first
except returns only the second record.
Source: on GitHub
# File activerecord/lib/active_record/associations/collection_proxy.rb, line 175
second_to_last() Link
Same as first
except returns only the second-to-last record.
Source: on GitHub
# File activerecord/lib/active_record/associations/collection_proxy.rb, line 224
select(*fields, &block) Link
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
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>
# ]
Source: on GitHub
# File activerecord/lib/active_record/associations/collection_proxy.rb, line 57
size() Link
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.
take(limit = nil) Link
Gives a record (or N records if a parameter is supplied) from the collection using the same rules as ActiveRecord::Base.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) # => []