Rails - Building a Query - Named Scope or?

I have the following models: Users, Groups, Conversations, ConversationParticipants( has a read boolean)

What开发者_StackOverflow中文版 I want to do is get an unread Count for a particular user in a particular group.

Should I be using a named_scope for this? If so, which model would this belong in (not sure)...

Also, I can do: @user.conversation_participations which then has the read field, problem is it does not have the group field as conversation_participations links to conversations (which has the group_id) via a conversation_id key.

Thoughts?

Thanks

You didn't show the code for the models, so I made some assumptions. Here's one way:

class Conversation < ActiveRecord::Base
  belongs_to :group
  has_many :conversation_participants
  has_many :participants, :through => :conversation_participants,\
    :source => :user

  scope :unread, lambda { |user,group| includes(:group,:conversation_participants).\
    where(:group_id => group.id,\
          :conversation_participants => {:read => false,:user_id => user.id})
  }
end

You're asking for "unread conversations belonging to a specific user and group". Since the thing being asked for is a set of Conversations, that's a natural place to put the scope.

EDIT

I see you wanted the count, not the result set. Just add .count to the scope:

Conversation.unread(user,group).count

EDIT 2

is it possible to do something like this instead to get the #, current_user.unread(group).count ..?

Add an instance method on User:

  def unread(group)
    Conversation.unread(self,group)
  end

Now you can call current_user.unread(group).count

If I understand the question correctly. I would use a named_scope in the ConversationParticipants called something like in_group:

scope :in_group, lambda do
  |group| joins(:conversation).where('conversation.group_id = ?', group.id)
end

I'm assuming the ConversationParticipants has belongs_to :conversation.

Now you can do:

@user.conversation_participations.in_group( some_group )