Rails - Dec 2005 - How do you paginate a SQL result with conditions?

Hi guys and gals,

I''ve been googling and scouring the wiki and re-reading the agile book 
for hours to no avail.

Can someone please explain to me in a nutshell how I can paginate a 
result with conditions?  Here''s a simple example.


## Model ##
def index
  @members =  Member.find_by_first_name(''Sean'')
end


## Controller ##
def members
    @member_pages, @members = paginate :members, :per_page => 40
end


## View ##
<%= render_partial "partial/paginator", @member_pages %>


... then I''ve got a partial that does the actual links and stuff.

Everything works great except that my pages show all results in the 
database, not just the ones with first_name of ''Sean''.  What
am I doing
wrong?  This is driving me crazy :-)

-- 
Posted via http://www.ruby-forum.com/.

Sean Schertell wrote:
> Hi guys and gals,
>
> I''ve been googling and scouring the wiki and re-reading the agile
book
> for hours to no avail.
>
> Can someone please explain to me in a nutshell how I can paginate a 
> result with conditions?  Here''s a simple example.
>   
[snip]

I had some trouble with finding good examples.

Have a look here: 
http://api.rubyonrails.org/classes/ActionController/Pagination.html

I adapted the ''custom'' pagination example to get this example
which
paginates users by current domain:

  def list
    @user_pages = Paginator.new self,
                   User.count(["domain_id = ?",
session[:user].domain_id]),
                   20,
                   @params[''page'']
    @users = User.find(:all, :order => ''last_name'',
                             :limit  =>  @user_pages.items_per_page,
                             :offset =>  @user_pages.current.offset,
                             :conditions => ["domain_id = ?", 
session[:user].domain_id])
  end

I''m a noob, so I''d appreciate feedback if I''m doing
something dumb here.

Regards,
John

John Dell wrote:
> def list
>    @user_pages = Paginator.new self,
>                   User.count(["domain_id = ?", 
> session[:user].domain_id]),
>                   20,
>                   @params[''page'']
>    @users = User.find(:all, :order => ''last_name'',
>                             :limit  =>  @user_pages.items_per_page,
>                             :offset =>  @user_pages.current.offset,
>                             :conditions => ["domain_id = ?", 
> session[:user].domain_id])
>  end
>
> I''m a noob, so I''d appreciate feedback if I''m
doing something dumb here.
Well, I can pick on myself.  Such is the rate of my progress with RoR 
:-), I saw somebody do this in another email thread so the above becomes:

  def list
    @user_pages, @users = paginate :user, {
      :per_page => 20,
      :conditions => ["domain_id = ?", session[:user].domain_id],
    }
  end

Much cleaner and nicer!

> Much cleaner and nicer!
I think I get it.  So that means that the "fully-automated" version of
the paginate helper is only for paginating raw database tables with no 
conditions?

-- 
Posted via http://www.ruby-forum.com/.

Sean Schertell wrote:
> I think I get it.  So that means that the "fully-automated"
version of
> the paginate helper is only for paginating raw database tables with no 
> conditions?
>   
Sorry I didn''t say that explicitly.  But yes, without :conditions you 
are paginating the entire model (table).

Regards,
John

Thanks for being so helpful guys.  One more thing I''m still unclear 
about though.  If my model fetches a table with conditions, can''t I
just
use that instance variable ( @live_members in my example ) instead of 
repeating myself in the controller?  In other words, doesn''t it make 
sense to set my conditions in the model and then just paginate that?

Sean



jdell wrote:
> Sean Schertell wrote:
>> I think I get it.  So that means that the "fully-automated"
version of
>> the paginate helper is only for paginating raw database tables with no 
>> conditions?
>>   
> Sorry I didn''t say that explicitly.  But yes, without :conditions
you
> are paginating the entire model (table).
> 
> Regards,
> John

-- 
Posted via http://www.ruby-forum.com/.

Sean Schertell wrote:
> Thanks for being so helpful guys.  One more thing I''m still
unclear
> about though.  If my model fetches a table with conditions, can''t
I just
> use that instance variable ( @live_members in my example ) instead of 
> repeating myself in the controller?  In other words, doesn''t it
make
> sense to set my conditions in the model and then just paginate that?
>   
Hmm.  My 2 cents... The only place I have my conditions in the 
controller are in the ''list'' method for pagination.  I
don''t see how
that''s any more work than putting it in the model.  Also, if you do put
it in the model (again not sure what that would look like), then it 
seems to me that you have crippled the model.  The model is for 
modelling and the controller is for controlling.  I think you would be 
trying to put controller type logic in the model if you did that.

Regards,
John

I see your point John.  Thanks for the interesting conversation.  My 
idea of putting some simple conditions in the model was stolen from page 
68 of the AWDR book where Dave says:
-----
We want to program at a decent level of abstraction, so let’s just 
assume we can ask the model for
a list of the products we can sell.

def index
  @products = Product.salable_items
end
-----

It seemed like a smart idea at the time, but I think your reasoning 
makes sense -- keep the login in the controller.  Any thoughts on this? 
Has Dave Thomas led me astray?

Sean




jdell wrote:
> Sean Schertell wrote:
>> Thanks for being so helpful guys.  One more thing I''m still
unclear
>> about though.  If my model fetches a table with conditions,
can''t I just
>> use that instance variable ( @live_members in my example ) instead of 
>> repeating myself in the controller?  In other words, doesn''t
it make
>> sense to set my conditions in the model and then just paginate that?
>>   
> Hmm.  My 2 cents... The only place I have my conditions in the
> controller are in the ''list'' method for pagination.  I
don''t see how
> that''s any more work than putting it in the model.  Also, if you
do put
> it in the model (again not sure what that would look like), then it
> seems to me that you have crippled the model.  The model is for
> modelling and the controller is for controlling.  I think you would be
> trying to put controller type logic in the model if you did that.
> 
> Regards,
> John

-- 
Posted via http://www.ruby-forum.com/.

Hi Sean,

Sean Schertell wrote:
> I see your point John.  Thanks for the interesting conversation.  My 
> idea of putting some simple conditions in the model was stolen from page 
> 68 of the AWDR book where Dave says:
> -----
> We want to program at a decent level of abstraction, so let’s just 
> assume we can ask the model for
> a list of the products we can sell.
>
> def index
>   @products = Product.salable_items
> end
> -----
>
> It seemed like a smart idea at the time, but I think your reasoning 
> makes sense -- keep the login in the controller.  Any thoughts on this? 
> Has Dave Thomas led me astray?
>   
Hmm.  I guess it comes down to how to implement ''proper'' MVC. 
I just
read that page in Dave''s book and on further reflection, I think you
are
right (can''t argue with Dave!)

I re-implemented a few of my models with this technique and removed the 
extra :condition logic from my controller and I like it.  I think I just 
learned something important about MVC that I didn''t understand before.
My definition of what a controller does was a bit skewed, I''ve been 
putting too much ''model'' logic in my controllers.

For a more difficult model than''s Dave''s example, the model
SQL would
likely require dynamic :conditions that vary with user input.  So the I 
guess the controller would pass the arguments to the model, which would 
be responsible for constructing the query and return the result.   So, 
is the model responsible for validating the SQL arguments, or does the 
controller do that?

Talk about a win-win, I try to answer your question and you end up 
teaching me about to better structure my code!

John

John Dell wrote:
> I re-implemented a few of my models with this technique and removed 
> the extra :condition logic from my controller and I like it.  I think 
> I just learned something important about MVC that I didn''t
understand
> before.  My definition of what a controller does was a bit skewed, 
> I''ve been putting too much ''model'' logic in my
controllers.
Sorry, I spoke too soon.  I thought it was working, but my example was 
too simple.  I now have the same problem that Sean had when he 
originally posted this question! 

It seems to me that this is a design choice or a limitation of 
paginate.    I can''t make paginate use a custom method in my model that
implements find and already has :conditions.  I tried the :class_name 
option to force it to use my method in paginate, but I couldn''t get
that
to work either. 

So, I''m back to my revised solution. I''d be happy for someone
enlighten
us on how to paginate a custom model method that has the conditions in 
the model.  Or, perhaps explain why this shouldn''t be done?

Thanks!
John