Saari Development

Ali Rizvi's Technical Blog as a Professional Software Development Engineer

Archive for the ‘code’ Category

Rails: Non-DB field in Model with validation

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Challenge: Add a field to the model representing system date, time & timezone that is not stored in the database and have validation on it.


  • Add attr_accessor & attr_accessible (for bulk update), add getter (sys_date_time) & setter (sys_date_time=) methods.
  • Return system date time in UTC from getter and show in user (browser) timezone on client side (using moment-timezone.js which is moment.js extension select the download with timezone data)
  • When the setting come to be saved using update_attributes in controller it eventually calls model setter (sys_date_time=) where you convert it back to utc given the timezone info (ActiveSupport::Timezone[zone] is your friend with ActiveSupport::TimeZone[zone].parse then in_time_zone(‘UTC’))
  • Validation is tricky as this is not a db backed and getter returns the calculated value which is always valid. You need to validate input first thing in setter and set a new member variable with errors found. Then add a validate do … end block where you iterate through the new member variable with errors and do errors.add(attr, message).

Will add code snippets when time permits.



Written by imsaar

April 7, 2016 at 2:02 pm

Posted in code, rails, ruby

My Advice To New Software Developers

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  • Don’t settle too early and don’t artificially constraint yourself. For instance:
    • Don’t say I am a Java or .NET developer and restrict yourself to only those platforms
    • Don’t stay in the same company for too long, some times you settle for 1 year of experience repeated 5 times rather than 5 years of real experience. You can always come back to a company if you like it better than the next one. In large companies you can move to a different group.
    • Don’t move too fast, take the time to learn from the smart people around you. If you are the smartest person there leave immediately.
  • Keep learning new and perspective changing technologies and not learn more of the same. For instance:
    • If you know a object oriented language (C++) learn functional language like Haskell
    • If you know a statically typed language (Java) learn a dynamically typed language like Ruby
    • Keep an eye on the trending technologies and briefly explore them to get a taste of them
  • Teach what you have learned to others, you have learned it if you can teach it

Written by imsaar

September 3, 2014 at 12:37 pm

Using Adobe’s New Source Code Fonts in Sublime Text 2 on Mac

with one comment

I just tweeted how much I love using the newly discovered Adobe Code fonts in Sublime Text 2 and though I should document the steps I followed to use them:

  1. Download font from Adobe Sourceforge: Source Sans Pro & Source Code Pro
  2. The easiest way I found to install all the font files on a Mac was to go to the terminal; cd to the downloaded font directory and type:

    open *.otf

  3. All the files will open in the Font Book app; Click “Install” button for each of them
  4. Now to use it open Sublime Text 2; open Preference -> Settings – User
  5. Add the following lines to the existing settings (if empty add these lines inside braces {}) to use the Light version of Source Sans Pro font in Size 17

    "font_size": 17.0,
    "font_face": "Source Code Pro Light"
    //"font_face": "Source Sans Pro Light"

  6. You can toggle the “//” on the two lines to try out the other font and adjust the font size as you prefer

Happy Coding!!!

Written by imsaar

September 28, 2012 at 9:21 am

Posted in code, editor, macosx

Ruby: Add a prefix to all files in a directory

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I found myself looking for a way to rename all files in a directory by appending a prefix and couldn’t find a utility to do such a renaming after quick search so I wrote my own.

# Quick script to bulk prepend prefix to filenames to all files in a directory
# Also strips any spaces in the filename
# Example usage : ruby prepend_rename.rb Disc1_ C:\AudioBook\Disc1\

raise "Prefix and Directory are required" if ARGV.size < 2

prefix = ARGV[0]
dir = ARGV[1]

raise "Non-word character prefix #{prefix}" unless prefix =~ /^\w+$/
raise "No such directory: #{dir}" unless Dir.exists?(dir)

Dir.entries(dir).each do |file|
 next if
 new_name = prefix + file.gsub(/\s+/, '')
 File.rename(file, new_name)

Written by imsaar

February 7, 2010 at 6:11 pm

Posted in code, ruby, windows

Rails: Skipping Base Class Filters in Subclasses

with 3 comments

I encountered a case where we needed to skip a filter as it was causing infinite redirection in a subclass. I found my answer in: Rails Filters Documentation

Filter chain skipping

Declaring a filter on a base class conveniently applies to its subclasses, but sometimes a subclass should skip some of its superclass’ filters:

  class ApplicationController < ActionController::Base
    before_filter :authenticate
    around_filter :catch_exceptions

  class WeblogController < ApplicationController
    # Will run the :authenticate and :catch_exceptions filters.

  class SignupController < ApplicationController
    # Skip :authenticate, run :catch_exceptions.
    skip_before_filter :authenticate

  class ProjectsController < ApplicationController
    # Skip :catch_exceptions, run :authenticate.
    skip_filter :catch_exceptions

  class ClientsController  :index

Written by imsaar

November 10, 2009 at 9:07 pm

Posted in code, documentation, rails, ruby

Java: Rediscovering the basics

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It’s been a while since I did some Java but now it seems to be the right tool for the job at hand so I am rediscovering Java with a masochistic twist, ‘look boss no IDEs’.

I am experimenting with the SSJ Java library for Stochastic Simulation as I mentioned in an earlier post and here is some sample source code:

import umontreal.iro.lecuyer.randvar.*;
import umontreal.iro.lecuyer.probdist.*;
import umontreal.iro.lecuyer.rng.*; 

public class GenerateDemandArrivals {
  private RandomStream randomStream;
  private RandomVariateGen expArrival;
  private RandomVariateGen poissonArrival;
  private double lambda;
  private int times;

  public GenerateDemandArrivals() {
    randomStream = new MRG32k3a();
    lambda = 10.0;
    times = 5;
    expArrival = new RandomVariateGen(randomStream, new ExponentialDist(lambda));
    poissonArrival = new PoissonGen(randomStream, new PoissonDist(lambda));


  public void demandArrival() {
    for (int i = 0; i < times; i++) {
      System.out.println("Here is the next random int : " + randomStream.nextInt(0, 10));

  public void demandArrivalExpDist() {
    for (int i = 0; i < times; i++) {
      System.out.println("Here is the next exponential dist double : " + expArrival.nextDouble());

  public void demandArrivalPoissonDist() {
    for (int i = 0; i < times; i++) {
      System.out.println("Here is the next poisson dist double : " + poissonArrival.nextDouble());

  public static void main(String&#91;&#93; arg) {
    new GenerateDemandArrivals().demandArrival();
    new GenerateDemandArrivals().demandArrivalExpDist();
    new GenerateDemandArrivals().demandArrivalPoissonDist();

I was tried of doing the following everytime I changed the source code in my favorite editor Vim:

javac -cp "C:\Program Files\Java\jdk1.6.0_02\lib\ext\ssj.jar;."
java -cp "C:\Program Files\Java\jdk1.6.0_02\lib\ext\ssj.jar;." GenerateDemandArrivals

I already had ant installed on my Windows machine but so I said why not take advantage of it, I looked for <a href="">simple ant file</a> and found something quite close in apache ant manual.

After little bit more search and refinement here is what I came up with:

<project name="Sim" default="run" basedir=".">
        simple example build file
  <!-- set global properties for this build -->
  <property name="src" location="."/>
  <property name="build" location="."/>
  <path id="project.class.path">
    <pathelement path="C:\Program Files\Java\jdk1.6.0_02\lib\ext\ssj.jar"/>
    <pathelement path="."/>

  <target name="run"
    description="run the program" 
    <java classname="GenerateDemandArrivals">
      <classpath refid="project.class.path"/>

  <target name="compile"
        description="compile the source " >
    <!-- Compile the java code from ${src} into ${build} -->
    <javac srcdir="${src}" destdir="${build}">
    <classpath refid="project.class.path"/>


Now I can simple type ant (while I am in the directory containing the build.xml file above) after any changes to the file and it compiles and run my code.

I feeling ashamed of feeling good and writing about such basic stuff but I am thinking there would be another person like me (could be myself at some future point where I have to leave my lovely Ruby world and come back to Java out of necessity).

Written by imsaar

November 20, 2008 at 7:06 pm

Posted in code, java

Tagged with , , , ,

JRuby: Stochastic Simulation with SSJ

with 2 comments

I needed to work on a simulation project that involved working with the SSJ java library.
If I haven’t mentioned before I love Ruby (the programming language) and Java, though a tool in my toolkit, does not evoke the same feeling.

So my first reaction was I can use JRuby to benefit from the existing java library and beauty of Ruby.
The SSJ library comes with a comprehensive sets of examples and documentation. I started exploring that.

Fortunately at RubyConf 2008 with some help from Charles Nutter I was able to install jruby on my laptop, getting jruby installed and running was not trivial. I wish somebody can do a one click installer for jruby same as they did for Ruby and Rails.

I downloaded SSJ and unzipped the downloaded file containing jar files into C:\Program Files\Java\jdk1.6.0_02\lib\ext directory. Added the CLASSPATH variable in my windows environment set to this directory.

I tried the following example from examples.pdf

import umontreal.iro.lecuyer.rng.*;
import umontreal.iro.lecuyer.stat.*;
public class Collision {
    int k; // Number of locations.
    int m; // Number of items.
    double lambda; // Theoretical expectation of C (asymptotic).
    boolean[] used; // Locations already used.
    public Collision (int k, int m) {
        this.k = k;
        this.m = m;
        lambda = (double) m * m / (2.0 * k);
        used = new boolean[k];
    // Generates and returns the number of collisions.
    public int generateC (RandomStream stream) {
        int C = 0;
        for (int i = 0; i < k; i++) used&#91;i&#93; = false;
        for (int j = 0; j < m; j++) {
            int loc = stream.nextInt (0, k-1);
            if (used&#91;loc&#93;) C++;
            else used&#91;loc&#93; = true;
        return C;
    // Performs n indep. runs using stream and collects statistics in statC.
    public void simulateRuns (int n, RandomStream stream, Tally statC) {
        for (int i=0; i<n; i++) statC.add (generateC (stream));
        System.out.println ( (0.95, 3));
        System.out.println (" Theoretical mean: " + lambda);
    public static void main (String&#91;&#93; args) {
        Tally statC = new Tally ("Statistics on collisions");
        Collision col = new Collision (10000, 500);
        col.simulateRuns (100000, new MRG32k3a(), statC);

I compiled and ran the Java code above to ensure I was getting the same results using the following steps:
javac -cp "C:\Program Files\Java\jdk1.6.0_02\lib\ext\ssj.jar"
java -cp "C:\Program Files\Java\jdk1.6.0_02\lib\ext\ssj.jar;C:\code\ruby\jruby" Collision

As you can notice my code was in the C:\code\ruby\jruby directory and I was in this directory when I ran the above program.

Here is the same code example in jruby code:

require 'java'
require 'ssj.jar'

import 'umontreal.iro.lecuyer.rng.RandomStream'
import 'umontreal.iro.lecuyer.stat.Tally'
import 'umontreal.iro.lecuyer.rng.MRG32k3a'

class Collision
  def initialize(k, m)
    @k = k
    @m = m
    @lambda = m * m / (2.0 * k)
    @used =, false)

  def generate_c(stream)
    c = 0
    @k.times { |i| @used[i] = false }
    @m.times do |j|
      loc = stream.nextInt(0, @k-1)
      if @used[loc]
        c += 1
        @used[loc] = true
    return c

  def simulate_runs(n, stream, stat_c)
   n.times { stat_c.add(generate_c(stream)) }
   puts, 3)
   puts " Theoretical mean: #{@lambda} "

    stat_c ="Statistics on collision")
    col =,500)
    col.simulate_runs(100000,, stat_c)


The jruby code runs comparatively slower (my feeling is 5 times slower but I will measure and add it later). I am using the latest available jruby 1.1.5 at the time of this post.

Update: The JRuby version takes around 13 minutes while the equivalent Java code above takes 17 seconds. This seems to be unacceptable performance, I am not sure if this is specific to SSJ or other libraries too. If I understand correctly, JRuby should be running inside the JVM and when I call SSJ library that is the same Java code that runs so I don’t understand why it is so slow unless I have used some technique that slows down my JRuby version.

Written by imsaar

November 15, 2008 at 10:25 pm

Posted in code, java, jruby, ruby