Loading part of a has_many association, and sorting as I add more elements

SeanWalberg · April 17, 2009, 6:12pm

Hello,

I have what boils down to a timesheet app. Before I display the entry form (eg one text input per day in the current schedule) I load the shifts I have in the database for the given period, then create new, blank shifts to fill in the blanks for the week before sorting the shifts by date and assigning to the relation.

This works in that if I have 2 shifts stored in the DB and want to display a week, the routine adds 5 more blank shifts and sorts. However, once I assign this to the relationship, the sorting seems to revert to created_by rather than the sort order of the array I assigned (example below)

class Shift < ActiveRecord::Base belongs_to :employee end

class Employee < ActiveRecord::Base has_many :shifts, :order => "date ASC"

def load_schedule(start, numdays)

raise "numdays must be >=1" if numdays < 1 # find the shifts that are already stored that are between start and start+numdays currentshifts = Shift.find( :all, :conditions => ["employee_id = :eid AND date >= :start AND date <= :finish", { :eid => self.id, :start => start.at_beginning_of_day, :finish => start.at_beginning_of_day +numdays.days-1.second } ] )

newshifts = Array.new # iterate through the week and create new shifts for the days that are missing # code omitted

# debugging stuff puts "============================================" c = newshifts.to_a + currentshifts.to_a puts "unsorted" c.each { |s| puts "#{s.date} - #{s.hours}" } d = c.sort_by { |a| a.date } puts "sorted" d.each { |s| puts "#{s.date} - #{s.hours}" } self.shifts = d puts "in employee object" self.shifts.each { |s| puts "#{s.date} - #{s.hours}" } end

The results of this are: .============================================ unsorted 2009-02-25 - 2009-02-26 - 2009-02-28 - 2009-03-02 - 2009-03-03 - 2009-02-27 - 1.5 2009-03-01 - 1.5 sorted 2009-02-25 - 2009-02-26 - 2009-02-27 - 1.5 2009-02-28 - 2009-03-01 - 1.5 2009-03-02 - 2009-03-03 - in employee object 2009-02-27 - 1.5 2009-03-01 - 1.5 2009-02-25 - 2009-02-26 - 2009-02-28 - 2009-03-02 - 2009-03-03 -

The reason I'm sorting and adding the blank shifts in the model is because I'm passing the object back up to the view where I'm using the FormHelpers to create the form. I'm loading a subset of the shifts at a time because it seems wasteful to load a year's worth of timesheet data if I'm only working with a week.

Why/how is the Array getting resorted when I assign it to the association? How do I stop it? Should I be working with a subset of the shift data this way, or is there a better way? Am I going about this completely wrong?

Thanks,

Sean

Frederick_Cheung · April 18, 2009, 1:10am

Why/how is the Array getting resorted when I assign it to the association? How do I stop it?

The key bit is the replace method in

github.com

rails/rails/blob/70de8e64e30092b2b1b77869e459b4868f5b9577/activerecord/lib/active_record/associations/association_collection.rb

require 'set'

module ActiveRecord
  module Associations
    # AssociationCollection is an abstract class that provides common stuff to
    # ease the implementation of association proxies that represent
    # collections. See the class hierarchy in AssociationProxy.
    #
    # You need to be careful with assumptions regarding the target: The proxy
    # does not fetch records from the database until it needs them, but new
    # ones created with +build+ are added to the target. So, the target may be
    # non-empty and still lack children waiting to be read from the database.
    # If you look directly to the database you cannot assume that's the entire
    # collection because new records may have beed added to the target, etc.
    #
    # If you need to work on all current children, new and existing records,
    # +load_target+ and the +loaded+ flag are your friends.
    class AssociationCollection < AssociationProxy #:nodoc:
      def initialize(owner, reflection)
        super

This file has been truncated. show original

It's trying to minimise the number of delete or updates to the database, so it first removes all the records that should no longer be there, then appends all the records that need to be added to the collection, which will mess with your order if the collection is non empty to begin with

If you reload the association the records should come out in the right order

Fred

SeanWalberg · April 18, 2009, 2:37pm

self.shifts = (newshifts.to_a + currentshifts.to_a).sort_by { |a| a.date } # Reload to get them in order self.shifts.reload

That seems to work (or at least passes my test cases ), thanks a lot!

Sean