class method self.default_scope

Use this macro in your model to set a default scope for all operations on the model.

class Article < ActiveRecord::Base
  default_scope where(:published => true)
end

Article.all # => SELECT * FROM articles WHERE published = true

The default_scope is also applied while creating/building a record. It is not applied while updating a record.

Article.new.published    # => true
Article.create.published # => true

You can also use default_scope with a block, in order to have it lazily evaluated:

class Article < ActiveRecord::Base
  default_scope { where(:published_at => Time.now - 1.week) }
end

(You can also pass any object which responds to call to the default_scope macro, and it will be called when building the default scope.)

If you use multiple default_scope declarations in your model then they will be merged together:

class Article < ActiveRecord::Base
  default_scope where(:published => true)
  default_scope where(:rating => 'G')
end

Article.all # => SELECT * FROM articles WHERE published = true AND rating = 'G'

This is also the case with inheritance and module includes where the parent or module defines a default_scope and the child or including class defines a second one.

If you need to do more complex things with a default scope, you can alternatively define it as a class method:

class Article < ActiveRecord::Base
  def self.default_scope
    # Should return a scope, you can call 'super' here etc.
  end
end