Iterating over a has_many collection within a named_scope

Here are my models:

class Message < ActiveRecord::Base
  has_many :comments

  attr_accessible :read #bool

  def unread_comments?
    comments.each { |comment| return true unless comment.read?}

    false
  end
end

class Comment < ActiveRecord::Base
  belongs_to :message

  attr_accessible :read #bool
end

Here is what I am looking to do: I'd like to c开发者_如何学Goreate a named_scope in Message, called unread that basically returns true if any of the message's comments are unread or the message itself is unread. Is there a way I can do this?

class Message < AR::Base
  ...
  def unread?
    !self.read && !self.comments.all?(&:read)
  end
end

How about this:

named_scope :unread, :conditions => ['messages.read = ? OR comments.read = ?', 
                                      false, false],
                     :include => :comments

Why the named scope? You could just do

def has_unread
  !self.read || unread_comments?
end

or, if it needs to be a class method

def self.has_unread(message)
  msg = Message.find(message.id)
  msg.read == false && msg.unread_comments?
end

Is you really do want to use named scopes though, you'll want something like this:

scope :get_unreads, lambda {|message|
  { :joins => :comments,
    :conditions => {:comments => {:message_id => message.id}, :message => ['read',0]},
    :select     => "DISTINCT `clients`.*" # kill duplicates
  }
}
def self.has_unread?(message)
  self.get_unreads(message).exists? && self.find(message.id).read
end