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Keith Salisbury

2007-May-10 11:22 UTC

Pagination has many through problems

I have searched for days for an example that demonstrates what i would
like to do, and this morning i thought i''d worked it out, but
no....here''s what i have:

Controller
=========
class ProfilesController < ApplicationController
 def friends
   current_user.profile.friends
 end
 def list_friends
   @profile_pages, @profiles = paginate( friends, :per_page => 10)
 end
end


Models
=====
class Profile < ActiveRecord::Base
 has_many :friendships
 has_many :friends,
          :through => :friendships
end

class Friendship < ActiveRecord::Base
 belongs_to :profile
 belongs_to :friend, :class_name => "Profile", :foreign_key =>
"friend_id"
end


When accessing "http://localhost:3000/profiles/list_friends" i get the
error:

"#<Profile:0x10ee01b4>#<Profile:0x10ee018c>" is not a
valid constant
name!

Any help gratefully recieved!!

keith

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Yuri Leikind

2007-May-10 11:27 UTC

head link

Re: Pagination has many through problems

Hey,

The first option to paginate expects the Symbol object which is the
name of your table, not an ActiveRecord or a list of ActiveRecord
objects.

Cheers,
Yuri

On 5/10/07, Keith Salisbury
<rails-mailing-list-ARtvInVfO7ksV2N9l4h3zg@public.gmane.org>
wrote:>
> I have searched for days for an example that demonstrates what i would
> like to do, and this morning i thought i''d worked it out, but
> no....here''s what i have:
>
> Controller
> =========>
> class ProfilesController < ApplicationController
>  def friends
>    current_user.profile.friends
>  end
>  def list_friends
>    @profile_pages, @profiles = paginate( friends, :per_page => 10)
>  end
> end
>
>
> Models
> =====>
> class Profile < ActiveRecord::Base
>  has_many :friendships
>  has_many :friends,
>           :through => :friendships
> end
>
> class Friendship < ActiveRecord::Base
>  belongs_to :profile
>  belongs_to :friend, :class_name => "Profile", :foreign_key
=>
> "friend_id"
> end
>
>
> When accessing "http://localhost:3000/profiles/list_friends" i
get the
> error:
>
> "#<Profile:0x10ee01b4>#<Profile:0x10ee018c>" is not a
valid constant
> name!
>
> Any help gratefully recieved!!
>
> keith
>
> --
> Posted via http://www.ruby-forum.com/.
>
> >
>

-- 
Best regards,
Yuri Leikind

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Keith Salisbury

2007-May-10 12:20 UTC

head link

Re: Pagination has many through problems

Yuri Leikind wrote:> The first option to paginate expects the Symbol object which is the
> name of your table, not an ActiveRecord or a list of ActiveRecord
> objects.
Hey Yuri,

Thanks for replying so quickly!!

So does this mean i am unable to paginate a recordset that is the result 
of two tables joined?

From the models you can see the only way for me to derive a list of 
"friends" is from the "friendships" table.

So do i have to paginate that, and then request the "profile" for each
friendship?

thanks
keith

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Yuri Leikind

2007-May-10 12:27 UTC

head link

Re: Pagination has many through problems

One of the options is having the following method in your ApplicationController

  def paginate_collection(collection, options = {})
    default_options = {:per_page => 10, :page => params[:page]}
    options = default_options.merge(options)

    pages = Paginator.new(self, collection.size, options[:per_page],
options[:page])
    first = pages.current.offset
    last = [first + options[:per_page], collection.size].min
    slice = collection[first...last]
    return [pages, slice]
  end

This method receives the collection as you see, and returns exactly
what paginate returns. The disadvantage of this solution is that you
have to read the _whole_ list of objects into memory. Though, well,
your initial variant does the same  :)

Cheers.


On 5/10/07, Keith Salisbury
<rails-mailing-list-ARtvInVfO7ksV2N9l4h3zg@public.gmane.org>
wrote:>
> Yuri Leikind wrote:
> > The first option to paginate expects the Symbol object which is the
> > name of your table, not an ActiveRecord or a list of ActiveRecord
> > objects.
>
> Hey Yuri,
>
> Thanks for replying so quickly!!
>
> So does this mean i am unable to paginate a recordset that is the result
> of two tables joined?
>
> From the models you can see the only way for me to derive a list of
> "friends" is from the "friendships" table.
>
> So do i have to paginate that, and then request the "profile" for
each
> friendship?
>
> thanks
> keith
>
> --
> Posted via http://www.ruby-forum.com/.
>
> >
>

-- 
Best regards,
Yuri Leikind

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Keith Salisbury

2007-May-10 14:20 UTC

head link

Re: Pagination has many through problems

Many thanks Yuri, i did actually have that in my application controller 
from previous attempts, but you''re right it does do exactly what
i''m
looking for.

For anyone looking for the solution, after including Yuri''s suggested 
method in my application controller, my profiles controller eventually 
looks like this:

class ProfilesController < ApplicationController
  def list_friends
    @friends = current_user.profile.friends
    @profile_pages, @profiles = paginate_collection(@friends, :page => 
params[:page])
  end
end

This does work as expected, however the scalability issue does concern 
me, and i''ve been trying to absorb and understand as much as possible 
about this problem.

Yuri:

Do you have any specific advice with regards to this issue?

I had read through this post 
(http://www.igvita.com/blog/2006/09/10/faster-pagination-in-rails/) 
which suggests the use of paginating_find plugin, but i dont see how 
this could be used with more than one model.

thanks
keith

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alexkwolfe-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org

2007-May-10 16:47 UTC

head link

Re: Pagination has many through problems

Hi Keith.  I know we emailed on this already, but I thought I''d post
this for others.  In your situation, paginating_find works like this:

@friends = current_user.profile.friends.find(:all, :page => { :size =>
10, :current => params[:page] })

... which, of course, gets you 10 friends associated with the current
user (through the profile).  Which 10 friends depends on the value of
params[:page].  So, no more loading *all* the friends if you only want
to show 10 of them at a time...



On May 10, 9:20 am, Keith Salisbury
<rails-mailing-l...-ARtvInVfO7ksV2N9l4h3zg@public.gmane.org>
wrote:> Many thanks Yuri, i did actually have that in my application controller
> from previous attempts, but you''re right it does do exactly what
i''m
> looking for.
>
> For anyone looking for the solution, after including Yuri''s
suggested
> method in my application controller, my profiles controller eventually
> looks like this:
>
> class ProfilesController < ApplicationController
>   def list_friends
>     @friends = current_user.profile.friends
>     @profile_pages, @profiles = paginate_collection(@friends, :page =>
> params[:page])
>   end
> end
>
> This does work as expected, however the scalability issue does concern
> me, and i''ve been trying to absorb and understand as much as
possible
> about this problem.
>
> Yuri:
>
> Do you have any specific advice with regards to this issue?
>
> I had read through this post
> (http://www.igvita.com/blog/2006/09/10/faster-pagination-in-rails/)
> which suggests the use ofpaginating_findplugin, but i dont see how
> this could be used with more than one model.
>
> thanks
> keith
>
> --
> Posted viahttp://www.ruby-forum.com/.

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