From: Josh Cheek <josh.cheek@...>
Date: 2010-01-16T02:53:33+09:00
Subject: Re: Binding scope

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On Fri, Jan 15, 2010 at 8:42 AM, Dave Birch <thisisdaveb@gmail.com> wrote:

> To give you a bit of background to this - I've got a "macro" that is
> generating a bunch of reports.  The reports contain lines like "the
> number of people in this group are X and they have spent a total of Y on
> your product this year".  The problem is, I can't substitute X and Y for
> their real values at the time the macro runs, because I don't know what
> filters the user will apply when viewing the reports.  So I need a way
> to do the calculations and substitute in the values when the user views
> the report, and to recalculate these each time the user changes the
> filter (e.g. show me only people older than 30).
>
> So unless I'm missing something, I can't keep a live object.
>
> It's a rails app, and the controller will be pulling together a
> "@results" variable, but will not necessarily know what kinds of stats
> need to be pulled from it.  That's why i'd like to be able to do things
> like "the number of people in this group are <code>@results.size</code>
> and they spent <code>@results.collect(&:spend).sum</code> on your
> product this year".
>
>
I don't really see the benefit of storing the template in the database, but
here is what I came up with.

require 'rubygems'
require 'activerecord'
require 'sqlite3'
require 'erb'


# documentation at http://www.sqlite.org/lang_createtable.html
db = SQLite3::Database.new( 'store_and_execute_strings.db' )
db.execute <<-__________________________________________________
              CREATE TABLE IF NOT EXISTS reports (
                id INTEGER PRIMARY KEY ASC AUTOINCREMENT,
                title Text,
                template TEXT
              );
              __________________________________________________

db.execute <<-__________________________________________________
              CREATE TABLE IF NOT EXISTS groups (
                id INTEGER PRIMARY KEY ASC AUTOINCREMENT,
                name STRING
              );
              __________________________________________________

db.execute <<-__________________________________________________
              CREATE TABLE IF NOT EXISTS people (
                id INTEGER PRIMARY KEY ASC AUTOINCREMENT,
                group_id INTEGER,
                money_spent DOUBLE,
                age INTEGER
              );
              __________________________________________________


# documentation at http://api.rubyonrails.org/classes/ActiveRecord/Base.html
# for other (better, depending on your needs) documentation, see
http://guides.rubyonrails.org/active_record_querying.html
#
http://guides.rubyonrails.org/association_basics.html
#
http://guides.rubyonrails.org/activerecord_validations_callbacks.html
ActiveRecord::Base.establish_connection :adapter   =>
'sqlite3'                        ,
                                        :host      =>
'localhost'                      ,
                                        :database  =>
'store_and_execute_strings.db'   ,
                                        :username  =>
'root'                           ,
                                        :password  =>  ''

class Report < ActiveRecord::Base
  def generate( &init )
    dup.instance_eval {
      instance_eval &init if init
      ERB.new( template , 0 , "%<>" ).result( binding )
    }
  end
end

class Group < ActiveRecord::Base
  has_many :people
end

class Person < ActiveRecord::Base
  belongs_to :group
end



# here is an example, as I understand your criteria

text_for_report = "the number of people in this group are <%= @people.length
%> and they have spent "   \
                  "a total of $<%= @people.inject(0) { |sum,person|
sum+person.money_spent.to_f } %> "  \
                  "on your product this year"

Report.new( :template => text_for_report , :title => 'Customer Summary'
).save

doctors = Group.new :name => 'doctors'
doctors.save

(1..10).each do |num|
  money , age  =  num , 20+num*5
  doctors.people.build( :money_spent => money , :age => age ).save
end

customer_summary = Report.find_by_title 'Customer Summary'

puts customer_summary.generate { @people =
doctors.people                                       }
puts customer_summary.generate { @people = doctors.people.all :conditions =>
'money_spent <= 5' }
puts customer_summary.generate { @people = doctors.people.all :conditions =>
'age < 40'         }

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