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

# File activerecord/lib/active_record/base.rb, line 1268
        def default_scope(scope = {})
          scope = Proc.new if block_given?
          self.default_scopes = default_scopes + [scope]
        end

class Article
default_scope :conditions => {:published => true}
end

Article.new.published? # => true

class Article
default_scope :conditions => 'published = 1'
end

Article.new.published? # => false

class Article < ActiveRecord::Base
scope :active, proc {
  where("expires_at IS NULL or expires_at > '#{Time.now}'")
}

scope :by_newest, order("created_at DESC")

default_scope by_newest
end

default_scope { active.by_newest }