Combine two named scopes with OR (instead of AND)

I couldn’t find any simple solutions, but this problem intrigued me, so I rolled my own solution:

class ActiveRecord::Base

  def self.or_scopes(*scopes)
    # Cleanup input
    scopes.map! do |scope|
      scope = scope.respond_to?(:to_a) ? scope.to_a : [*scope]
      scope.unshift(scope.shift.to_sym)
    end

    # Check for existence of scopes
    scopes.each{|scope| raise ArgumentError, "invalid scope: #{scope.first}" unless self.scopes.has_key?(scope.first) }

    conditions = scopes.map do |scope|
      scope = self.scopes[scope.first].call(self, *scope[1..-1])
      self.merge_conditions(scope.proxy_options[:conditions])
    end

    or_conditions = conditions.compact.join(" OR ")

    merged_scopes = scopes.inject(self){|merged, scope| merged.scopes[scope.first].call(self, *scope[1..-1]) }

    # We ignore other scope types but so does named_scopes
    find_options = merged_scopes.scope(:find).merge(:conditions => or_conditions)

    self.scoped(find_options)
  end

end

Consider the following setup:

class Person < ActiveRecord::Base
  named_scope :men,      :conditions => { :sex => 'M' }
  named_scope :women,    :conditions => { :sex => 'F' }
  named_scope :children, :conditions => "age < 18"
  named_scope :named, lambda{|name|
    { :conditions => { :name => name } }
  }
end

You call it with the names of a series of scopes as such:

Person.or_scopes(:women, :children)

This returns a scope like this:

Person.or_scopes(:women, :children).proxy_options
# => {:conditions=>"(`people`.`sex` = 'F') OR (age < 18)"}

You can also call it with an array of arrays when the scope requires parameters:

Person.or_scopes(:women, [:named, 'Sue']).proxy_options
# => {:conditions=>"(`people`.`sex` = 'F') OR (`people`.`name` = 'Sue')"}

In your case Horace, you could use the following:

Annotation.or_scopes([:body_equals, '?'], [:body_like, '[?']).all