Example
Scopes act as predefined filters on ActiveRecord models.
A scope is defined using the scope class method.
As a simple example, we will use the following model:
class Person < ActiveRecord::Base
#attribute :first_name, :string
#attribute :last_name, :string
#attribute :age, :integer
# define a scope to get all people under 17
scope :minors, -> { where(age: 0..17) }
# define a scope to search a person by last name
scope :with_last_name, ->(name) { where(last_name: name) }
end
Scopes can be called directly off the model class:
minors = Person.minors
Scopes can be chained:
peters_children = Person.minors.with_last_name('Peters')
The where method and other query type methods can also be chained:
mary_smith = Person.with_last_name('Smith').where(first_name: 'Mary')
Behind the scenes, scopes are simply syntactic sugar for a standard class method. For example, these methods are functionally identical:
scope :with_last_name, ->(name) { where(name: name) }
# This ^ is the same as this:
def self.with_last_name(name)
where(name: name)
end
Default Scope
in your model to set a default scope for all operations on the model.
There is one notable difference between the
scopemethod and a class method:scope-defined scopes will always return anActiveRecord::Relation, even if the logic within returns nil. Class methods, however, have no such safety net and can break chainability if they return something else.
