Question

I need to use my own pagination code because my needs are too varied and specific. I have this snippet copied and pasted in lots of controller actions

per_page = params[:per_page] ? params[:per_page].to_i : 15
page_num = params[:page] ? params[:page].to_i : 1
to_skip = ( page_num - 1 ) * (per_page)
max_index = per_page * page_num

The more i do this, the dumber I feel. I am sure there is a way to do this better, but I am not sure how.

BONUS (can i award bounty for this?) -> i would love to able to use the COMPUTED params in the model if i need to

Example:

# frontend requests for items 15-30

def controller_action
  # code as above
  # Item.get (...)
end

# and in the model have access to these params
def get
  # use per_page, to_skip 
end

Answer 1

I’d probably put this into the ApplicationController as a request filter

class ApplicationController < ActionController::Base
  protected
  def set_paging_params
    @per_page = params[:per_page] ? params[:per_page].to_i : 15
    @page_num = params[:page] ? params[:page].to_i : 1
    @to_skip = ( @page_num - 1 ) * (@per_page)
    @max_index = @per_page * @page_num
  end
end

class FooController < ApplicationController
  before_filter :set_paging_params, only: [:index]

  def index
    # do stuff with @per_page and others
  end
end

There’s no way for model to use these controller instance variables, unless you pass them explicitly (or capture them in a closure, but I’m don’t know if your Item.get implementation will support this). Something like this:

class FooController < ApplicationController
  before_filter :set_paging_params, only: [:controller_action]

  def controller_action
    Item.get(params[:id], per_page: @per_page,
      page_num: @page_num,
      to_skip: @to_skip,
      max_index: @max_index,
    )
  end
end

class Item
  def self.get iid, opts = {}
    # use opts[:per_page] here
  end
end