Ruby on Rails模型关联问题

Question

Sorry for the vague title, but it's a little much to explain in a sentence.

I've got three models, User, Device, and DeviceMessage. Their relationships are fairly simple:

• a User has_many :devices ,
• a Device belongs_to :user ,
• a Device has_many :device_messages ,
• and a DeviceMessage belongs_to :device .

Rails provides ways to start playing with these associations quickly, like the ability to get all device messages that belong to a certain user (from any device).

In order to do this, I defined a method in the User model:

    class User < ActiveRecord::Base
      ...
      has_many :devices, :as => : owner #Other entities may "own" a device

      def device_feed
        DeviceMessage.that_belong_to_user(self)
      end
    end

And I define the called method in the DeviceMessage model:

    class DeviceMessage < ActiveRecord::Base
      ...
      belongs_to :device

      def self.that_belong_to_user(user)
        device_ids = "SELECT owner_id FROM devices WHERE owner_id = :user_id 
                     AND owner_type = \"User\""
        where("device_id IN (#{device_ids})", user_id: user.id)
      end
    end

I define a user page where they can associate a device to their account (the device has a name as well), and upon adding the device to the account, it will add the name to a list of device names in a pane to the left, while showing the user's device feed much like a twitter feed (yes, I followed Michael Hartl's RoR tutorial). At this point it is important to note that I am using helper functions to keep track of the current user so I can display this information when a user visits the root_path while logged in. When visiting the root_path, the controller for the root_path is defined so that:

    if user_signed_in?
      @device_feed_items = current_user.device_feed.paginate(page: params[:page])
    end

And this all works perfectly!

So... what's the issue? When I create a new user via the signup page, and associate the device via the device-association page, I am redirected to the root_path, the device name is correctly displayed in the left pane (which mean the device is correctly associated with the new user), but the device_feed is not displayed.

I've used the Rails console to verify that the device messages should be showing ( User.find(2).devices.first.device_messages.first displays the first message associated with the first device that is newly associated with the 2nd user), so I know that I need to reach down into the database to get a fresh rather than cached copy of the current_user, but I'm confused because it seems like that should be happening every time the user.device_feed method is called because of it's use of where() which is a part of the query API...

Any ideas? Thanks in advance for any and all answers.

-MM

Answer 1

I am just wondering why you have the device_feed function. For your feed display could you not just a loop like this one, this is

class Device < ActiveRecord::Base

  scope :in_new_message_order, :joins => :device_messages, :order => "created_at DESC"      

end

Added a joined scope

class User < ActiveRecord::Base
  ...
  has_many :devices, :as => : owner #Other entities may "own" a device
  scope :in_sort_order, order("message_date DESC")

  def device_feed
    DeviceMessage.that_belong_to_user(self)
  end
end

Above I have added a scope to sort your messages

<% user.devices.in_new_message_order.each do |device| %>
    <% device.device_messages_in_sort_order.each do |message| %>
        <%= ....render out the message %>
    <% end %>
<% end %>