Rails - Feb 2010 - Model validation dependent upon session data being set?

Ok so I have a few models that need to interact with each other -
Blog, Post, and User.  I''ll get their relationships out of the way:

Blog
  has_many :posts
  has_and_belongs_to_many :users (by way of a join table, a blog can
have many contributing users)

Post
  belongs_to :blog
  belongs_to :user (the author of the post)

User
  has_and_belongs_to_many :blogs (a user can contribute to many blogs)
  has_many :posts


I''m running into a problem when validating posts; I want to ensure
that the logged in user we find in the session is listed as a
contributor to the blog they are trying to post to.  I added some
validation to my Post model, that appears to be failing when editing
an existing post.  Post creation, curiously, seems to pass the
validation test.

I should note that @user is a variable set by my ApplicationController
using a before_filter.  really sure what''s going on here, so any help
is appreciated.  I''m guessing the @user set by my app controller
probably isn''t accessible by the Post class.

Anyhow, here''s my Post model:

class Post < ActiveRecord::Base
  belongs_to :blog
  belongs_to :user
  has_many :comments

  validate :user_can_contribute

private
  def user_can_contribute
    if @user.nil?
      logger.info("@user hasn''t been set yet!")
    end

    if !blog.users.include?(@user)
      errors.add(:user, "You cannot contribute to this blog.")
    end
  end
end

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Actually, I''m not so sure if post creation is passing the validation
test either :)

Sorry for being confusing.

On Feb 27, 11:09 am, robo
<chase.delanguille...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
> Ok so I have a few models that need to interact with each other -
> Blog, Post, and User.  I''ll get their relationships out of the
way:
>
> Blog
>   has_many :posts
>   has_and_belongs_to_many :users (by way of a join table, a blog can
> have many contributing users)
>
> Post
>   belongs_to :blog
>   belongs_to :user (the author of the post)
>
> User
>   has_and_belongs_to_many :blogs (a user can contribute to many blogs)
>   has_many :posts
>
> I''m running into a problem when validating posts; I want to ensure
> that the logged in user we find in the session is listed as a
> contributor to the blog they are trying to post to.  I added some
> validation to my Post model, that appears to be failing when editing
> an existing post.  Post creation, curiously, seems to pass the
> validation test.
>
> I should note that @user is a variable set by my ApplicationController
> using a before_filter.  really sure what''s going on here, so any
help
> is appreciated.  I''m guessing the @user set by my app controller
> probably isn''t accessible by the Post class.
>
> Anyhow, here''s my Post model:
>
> class Post < ActiveRecord::Base
>   belongs_to :blog
>   belongs_to :user
>   has_many :comments
>
>   validate :user_can_contribute
>
> private
>   def user_can_contribute
>     if @user.nil?
>       logger.info("@user hasn''t been set yet!")
>     end
>
>     if !blog.users.include?(@user)
>       errors.add(:user, "You cannot contribute to this blog.")
>     end
>   end
> end
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On 27 February 2010 17:09, robo
<chase.delanguillette-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
> Ok so I have a few models that need to interact with each other -
> Blog, Post, and User.  I''ll get their relationships out of the
way:
>
> Blog
>  has_many :posts
>  has_and_belongs_to_many :users (by way of a join table, a blog can
> have many contributing users)
>
> Post
>  belongs_to :blog
>  belongs_to :user (the author of the post)
>
> User
>  has_and_belongs_to_many :blogs (a user can contribute to many blogs)
>  has_many :posts
>
>
> I''m running into a problem when validating posts; I want to ensure
> that the logged in user we find in the session is listed as a
> contributor to the blog they are trying to post to.  I added some
> validation to my Post model, that appears to be failing when editing
> an existing post.  Post creation, curiously, seems to pass the
> validation test.
>
> I should note that @user is a variable set by my ApplicationController
> using a before_filter.  really sure what''s going on here, so any
help
> is appreciated.  I''m guessing the @user set by my app controller
> probably isn''t accessible by the Post class.
>
> Anyhow, here''s my Post model:
>
> class Post < ActiveRecord::Base
>  belongs_to :blog
>  belongs_to :user
>  has_many :comments
>
>  validate :user_can_contribute
>
> private
>  def user_can_contribute
>    if @user.nil?
>      logger.info("@user hasn''t been set yet!")
>    end
>
>    if !blog.users.include?(@user)
>      errors.add(:user, "You cannot contribute to this blog.")
>    end
>  end
> end
Have you tried using ruby-debug to break into the validation code and
see what is happening?  See the rails guide on debugging at
http://guides.rubyonrails.org/

Colin

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On 27 February 2010 17:09, robo
<chase.delanguillette-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
> I should note that @user is a variable set by my ApplicationController
> using a before_filter.  really sure what''s going on here, so any
help
> is appreciated.  I''m guessing the @user set by my app controller
> probably isn''t accessible by the Post class.
Yup - you''ve identified your problem perfectly... here''s a
suggested solution:

@user is a instance variable; that is, only available to the instance
of a class (in this instance, the controller). So you can''t access it
from an instance of a different class.
So you need to create a method on your controller that will return the
@user object. The convention for this method seems to be to call it
"current_user".

def current_user
  @user
end

Simple, huh? ;-)
Now you can get rid of that before_filter call, and do the operation
when/if somewhere calls "current_user" - so it''ll look more
like this:

def current_user
  @user ||= the_method_for_the_logic_that_works_out_the_logged_in_user
end


An other solution would be to use a wrapped-up plugin to do
authentication (there are lots to choose from), which would take all
you user/password management woes and deal with them for you (and most
likely give you a "current_user" method!)

HTH
Michael

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On 27 February 2010 19:24, Michael Pavling
<pavling-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
> So you need to create a method on your controller that will return the
> @user object. The convention for this method seems to be to call it
> "current_user".
>
*ahem*  Of course... an instance of a model doesn''t have access to
application_controller''s methods... I was getting carried away with
myself.
You will *also* need to pass this to the Post directly... so declare
an "attr_writer :current_user" on your Post model, and in the
controller, when you instanciate the Post, pass it the variable:

post = Post.find(params[:post_id] # or whatever...
post.current_user = current_user

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Hey, that did the trick.  Thanks for that!

On Feb 27, 1:36 pm, Michael Pavling
<pavl...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
> On 27 February 2010 19:24, Michael Pavling
<pavl...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
>
> > So you need to create a method on your controller that will return the
> > @user object. The convention for this method seems to be to call it
> > "current_user".
>
> *ahem*  Of course... an instance of a model doesn''t have access to
> application_controller''s methods... I was getting carried away
with
> myself.
> You will *also* need to pass this to the Post directly... so declare
> an "attr_writer :current_user" on your Post model, and in the
> controller, when you instanciate the Post, pass it the variable:
>
> post = Post.find(params[:post_id] # or whatever...
> post.current_user = current_user
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