MeantimeFilter: Wrap your Rails controller actions with scopes

By Peter Cooper / July 6, 2006

MeantimeFilter is an interesting new plugin for Rails by Roman Le Negrate. It's a little like around_filter, but rather than using a class with 'before' and 'after' methods, it uses a single method (like the other types of filter) and passes in the method to wrap 'around' as a code block. You can then yield to this or pass it into anything you like. An example:

class PostsController < ApplicationController
  before_filter :authenticate
  meantime_filter :scope_posts_to_user

  # Displays the posts of the logged in user.
  def show
    @posts = Post.find(:all)
  end

  def create
    # ...
    @post = Post.create(params[:post]) # Automatically associated to @user
    # ...
  end

  private

  # Sets @user to the logged in user or redirects to :index.
  def authenticate
    # ...
  end

  def scope_posts_to_user(&block)
    Post.with_scope({
      :find => { :conditions => [ 'user_id = ?', @user.id ]},
      :create => { :user => @user }
    }, &block)
  end

  # Or:
  def scope_posts_to_user
    Post.with_scope({
      :find => { :conditions => [ 'user_id = ?', @user.id ]},
      :create => { :user => @user }
    }) { yield }
  end
end

Hot! This could make your code a lot cleaner by allowing you to wrap any methods you want in a scope automatically.

Comments

Josh says:
July 6, 2006 at 12:57 pm
I'm confused. Why is this cleaner than @user.posts.create(params[:post])? I like yielding as much as the next guy, but I dungettit
Peter Cooper says:
July 6, 2006 at 1:22 pm
It can get a lot more complex than that. Consider when you nest scopes. His demonstration is a little simplistic, of course :)
Tony says:
July 7, 2006 at 6:21 pm
This looks really usefull, but I'm having trouble wrapping my head around how to use this for setting the same scope for a number of models? Short of doing this:

meantime_filter :scope_x_to_foo, :scope_y_to_foo, :scope_z_to_foo...

def scope_x_to_foo
x.with_scope({...})
end

def scope_y_to_foo
y.with_scope({...})
end

...

I guess I'm not grokking the way yield works... is there a more DRY way?
Tony says:
July 7, 2006 at 9:26 pm
In case anyone is curious I figured out how to do it pretty cleanly by passing a class instance. Basically I did this:

# Intranet.current_intranet is set by a before_filter...

class IntranetScopeFilter
def initialize(model_name)
@model_name = model_name
@model = Object.const_get(model_name)
end
def filter(controller)
if Intranet.current_intranet.nil?
yield
else
@model.with_scope({
:find => {:conditions => ["#{@model_name.downcase.pluralize}.intranet_id = ?",Intranet.current_intranet.id]},
:create => {:intranet_id => Intranet.current_intranet.id}
}) { yield }
end
end
end

meantime_filter IntranetScopeFilter.new("User")
meantime_filter IntranetScopeFilter.new("Contact")
meantime_filter IntranetScopeFilter.new("Matter")
...etc