Rails - Dec 2005 - custom find methods and pagination

i''ve got several methods in my models i use to find based on certain
criteria...i''ve done this so the controller code is less cluttered,
plus the
DRY factor.

example:

class Foo < ActiveRecord::Base

  def find_by_something(something)
    find :all, :joins => ..., :conditions => ...
  end

  def find_by_something_else(something_else)
    find :all, :joins => ..., :conditions => ...
  end

  def find_by_something_and_bar(something, bar)
    find :all, :joins => ..., :conditions => ...
end

now my question:

is there a way to do Foo.find_by_something(something) in a paginator?  would
I have to modify all my methods to accept a limit and offset parameter?

thanks


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I''ve been trying to do the same thing.  Is this possible or is the only
way to do this is putting your queries in the controller?
> now my question:
> 
> is there a way to do Foo.find_by_something(something) in a paginator? 
> would
> I have to modify all my methods to accept a limit and offset parameter?
> 
> thanks

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

Chris Hall wrote:
> i''ve got several methods in my models i use to find based on
certain
> criteria...i''ve done this so the controller code is less
cluttered, plus
> the DRY factor.
> 
> example:
> 
> class Foo < ActiveRecord::Base
> 
>   def find_by_something(something)
>     find :all, :joins => ..., :conditions => ...
>   end
> 
>   def find_by_something_else(something_else)
>     find :all, :joins => ..., :conditions => ...
>   end
> 
>   def find_by_something_and_bar(something, bar)
>     find :all, :joins => ..., :conditions => ...
> end
> 
> now my question:
> 
> is there a way to do Foo.find_by_something(something) in a paginator?  
> would I have to modify all my methods to accept a limit and offset 
> parameter?
This question seems to be asked a couple times a week on this list but 
never resolved.  I also banged my head against this and ultimately gave 
up and put my conditions in the controller/pagination rather than in the 
model where I''d like it to be.

I believe it can''t be done with the current paginator.  Hopefully, 
someone more knowledgeable can prove me wrong :-)

John

I had a hard time with custom pagination at first.  It was  
intimidating and I didn''t find any of the online guides particularly  
helpful.  So here''s mine.  :-)

Kevin''s custom-pagination-in-four-easy-steps:

def list

	# step 1: read and set the variables you''ll need
	page = (params[:page] ||= 1).to_i
	items_per_page = 20
	offset = (page - 1) * items_per_page

	# step 2: do your custom find without doing any kind of limits or  
offsets
	#  i.e. get everything on every page, don''t worry about pagination yet
	@items = Item.find_with_some_custom_method(@some_variable)

	# step 3: create a Paginator, the second variable has to be the  
number of ALL items on all pages
	@item_pages = Paginator.new(self, @items.length, items_per_page, page)

	# step 4: only send a subset of @items to the view
	# this is where the magic happens... and you don''t have to do  
another find
	@items = @items[ offset..(offset + items_per_page - 1)]

end


HTH,
Kevin Skoglund



> I''ve been trying to do the same thing.  Is this possible or is the
> only
> way to do this is putting your queries in the controller?
>
>
>> now my question:
>>
>> is there a way to do Foo.find_by_something(something) in a paginator?
>> would
>> I have to modify all my methods to accept a limit and offset  
>> parameter?
>>
>> thanks
>>

Kevin Skoglund wrote:
> I had a hard time with custom pagination at first.  It was  intimidating 
> and I didn''t find any of the online guides particularly  helpful. 
So
> here''s mine.  :-)
> 
> Kevin''s custom-pagination-in-four-easy-steps:
> 
> def list
> 
>     # step 1: read and set the variables you''ll need
>     page = (params[:page] ||= 1).to_i
>     items_per_page = 20
>     offset = (page - 1) * items_per_page
> 
>     # step 2: do your custom find without doing any kind of limits or  
> offsets
>     #  i.e. get everything on every page, don''t worry about
pagination yet
>     @items = Item.find_with_some_custom_method(@some_variable)
> 
>     # step 3: create a Paginator, the second variable has to be the  
> number of ALL items on all pages
>     @item_pages = Paginator.new(self, @items.length, items_per_page, page)
> 
>     # step 4: only send a subset of @items to the view
>     # this is where the magic happens... and you don''t have to do
> another find
>     @items = @items[ offset..(offset + items_per_page - 1)]
> 
> end
I suppose this is ok for small result sets, but the major problem with 
this approach is that for pagination of larger sets of data, this is 
going to be extremely inefficient.  The way the rails paginator works is 
it gets a count of ALL the records, but then only selects what is going 
to be displayed using the sql ''LIMIT'' clause.

John

>> I had a hard time with custom pagination at first.  It was   
>> intimidating and I didn''t find any of the online guides  
>> particularly  helpful.  So here''s mine.  :-)
>> Kevin''s custom-pagination-in-four-easy-steps:
>> def list
>>     # step 1: read and set the variables you''ll need
>>     page = (params[:page] ||= 1).to_i
>>     items_per_page = 20
>>     offset = (page - 1) * items_per_page
>>     # step 2: do your custom find without doing any kind of limits  
>> or  offsets
>>     #  i.e. get everything on every page, don''t worry about  
>> pagination yet
>>     @items = Item.find_with_some_custom_method(@some_variable)
>>     # step 3: create a Paginator, the second variable has to be  
>> the  number of ALL items on all pages
>>     @item_pages = Paginator.new(self, @items.length,  
>> items_per_page, page)
>>     # step 4: only send a subset of @items to the view
>>     # this is where the magic happens... and you don''t have to
do
>> another find
>>     @items = @items[ offset..(offset + items_per_page - 1)]
>> end
>
> I suppose this is ok for small result sets, but the major problem  
> with this approach is that for pagination of larger sets of data,  
> this is going to be extremely inefficient.  The way the rails  
> paginator works is it gets a count of ALL the records, but then  
> only selects what is going to be displayed using the sql
''LIMIT''
> clause.
>
> John
Yes, it is for small sets of data which require custom finds.

For larger sets of data which also require custom finds, you''ll have  
to modify step 2 to execute an SQL count of your custom find instead,  
modify the 2nd variable in step 3 to use that count, and then modify  
step 4 to do the full find with the SQL limit clause added.  I don''t  
know of a way around having to rewrite your object methods.

One thing that might help you is to set sensible default values in  
the object methods so that you don''t also have to immediately also  
rewrite all of your calls to that object method.  Something like:

def self.find_by_custom_method( some_variable, limit = nil, offset =  
nil )
	...
end

Then you can upgrade and paginate other calls at your leisure without  
breaking them.

Kevin

yeah, i figured that''d be the way i have to go.  thanks all for the
ideas.

On 12/19/05, Kevin Skoglund
<kevin-WGmuFPN42W8gMxX8nMqP6gC/G2K4zDHf@public.gmane.org>
wrote:
>
> >> I had a hard time with custom pagination at first.  It was
> >> intimidating and I didn''t find any of the online guides
> >> particularly  helpful.  So here''s mine.  :-)
> >> Kevin''s custom-pagination-in-four-easy-steps:
> >> def list
> >>     # step 1: read and set the variables you''ll need
> >>     page = (params[:page] ||= 1).to_i
> >>     items_per_page = 20
> >>     offset = (page - 1) * items_per_page
> >>     # step 2: do your custom find without doing any kind of limits
> >> or  offsets
> >>     #  i.e. get everything on every page, don''t worry
about
> >> pagination yet
> >>     @items = Item.find_with_some_custom_method(@some_variable)
> >>     # step 3: create a Paginator, the second variable has to be
> >> the  number of ALL items on all pages
> >>     @item_pages = Paginator.new(self, @items.length,
> >> items_per_page, page)
> >>     # step 4: only send a subset of @items to the view
> >>     # this is where the magic happens... and you don''t
have to do
> >> another find
> >>     @items = @items[ offset..(offset + items_per_page - 1)]
> >> end
> >
> > I suppose this is ok for small result sets, but the major problem
> > with this approach is that for pagination of larger sets of data,
> > this is going to be extremely inefficient.  The way the rails
> > paginator works is it gets a count of ALL the records, but then
> > only selects what is going to be displayed using the sql
''LIMIT''
> > clause.
> >
> > John
>
> Yes, it is for small sets of data which require custom finds.
>
> For larger sets of data which also require custom finds, you''ll
have
> to modify step 2 to execute an SQL count of your custom find instead,
> modify the 2nd variable in step 3 to use that count, and then modify
> step 4 to do the full find with the SQL limit clause added.  I
don''t
> know of a way around having to rewrite your object methods.
>
> One thing that might help you is to set sensible default values in
> the object methods so that you don''t also have to immediately also
> rewrite all of your calls to that object method.  Something like:
>
> def self.find_by_custom_method( some_variable, limit = nil, offset > nil
)
>         ...
> end
>
> Then you can upgrade and paginate other calls at your leisure without
> breaking them.
>
> Kevin
>
> _______________________________________________
> Rails mailing list
> Rails-1W37MKcQCpIf0INCOvqR/iCwEArCW2h5@public.gmane.org
> http://lists.rubyonrails.org/mailman/listinfo/rails
>

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