mig_constraints is not compatible with rails 2.3

Although it’s old, mig_constraints has sat in my rails plugin directory for a while now because it adds much needed foreign key support to ActiveRecord.

I’m on of those crazy guys that thinks a relational database should maintain relational integrity, so it’s been a staple of my rails projects for some time. Unfortunately when I recently upgraded to rails 2.3.4, it created a bizarre obscure error that seems to indicate it’s not compatible with rails 2.3 at all.

As far as I can tell, the best candidate for a replacement is this github project but I’ve not yet had the time to try it. For now I simply removed the plugin from my project and db:migrate reverted to a nice working state.

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Posted in Rails | Tagged , , | 3 Comments

Setting up a kick-ass rails server on Ubuntu 9.04 (Jaunty)

I recently created a new slicehost and thought I’d try the latest Ubuntu release with it. Unlike brightbox hosting, you only get a plain boring ubuntu installation out of the box on slicehost (and various other VPS-based hosting services).

A bit of aptitude

Ubuntu/Debian make it really nice and easy to install packages, but this time it still took me a couple of hours to install everything.

For my (and your) future reference, here’s all you need to create a full rails/mysql/apache platform on Ubuntu 9.04:

apt-get install rubygems ruby1.8-dev mysql-server-5.1 libmysqlclient15-dev apache2 libopenssl-ruby libxslt1-dev libcurl4-gnutls-dev build-essential apache2-prefork-dev libapr1-dev libaprutil1-dev libmagickwand-dev git-core subversion

gem install rails --version=2.2.2
gem install rake mysql passenger

cd /to/your/app
rake gems:install

Be sure to follow the instructions that appear after installing passenger, and then that’s it! Make sure you set the version number of rails that you need, or remove the –version parameter if you just want the latest stable release.

(Note: the last line assumes you’ve added all the gems your application requires to config/environment.rb. You could make the above list of packages even more minimal, but they cover plenty of common gem dependencies).

Going the extra mile

If you need to setup an environment to create screenshots programmatically, you’ll need a virtual X server, firefox and selenium (which is Java-based). That’s also fairly easy:

apt-get install xvfb firefox latex-xft-fonts sun-java6-jdk gsfonts-x11 sun-java6-fonts
gem install selenium-client

Do you have any must install packages when creating a new server? Please add them in the comments below.

Posted in Rails | 1 Comment

Wisdom from a different (Internet) age

It doesn’t happen very often, but I was pointed to an online article recently that dates back almost a decade. The Pitchman is a story by Malcolm Gladwell about “Ron Popeil, who invented a better rotisserie in his kitchen and went out and pitched it himself.”

“Like most great innovations, it was disruptive. And how do you persuade people to disrupt their lives? Not merely by ingratiation or sincerity, and not by being famous or beautiful. You have to explain the invention to customers– not once or twice but three or four times, with a different twist each time. You have to show them exactly how it works and why it works, and make them follow your hands as you chop liver with it, and then tell them precisely how it fits into their routine, and, finally, sell them on the paradoxical fact that, revolutionary as the gadget is, it’s not at all hard to use.”

“in every respect the design of the product must support the transparency and effectiveness of its performance during a demonstration – the better it looks onstage, the easier it is for the pitchman to … ask for the money.”

While Ron and the article are focused on gadgets and devices, the above holds true for any kind of innovation that you’re trying to convince people to buy, or in the case of a free service, just to use.

Posted in Starting up | Leave a comment

Nokogiri fails to work on Solaris (11), but fix it like this!

I’ll have a better fix up in the near future, but for now, the ruby gem “Nokogiri” crashed out on me on Joyent’s Solaris platform. Its error was a little cryptic unless you’re familiar with libc. I can’t reproduce it here because unfortunately it’s lost in the sands of scrollback buffer.

The crux of the problem was the reference to a missing vasprintf function. Nokogiri has an extension implemented in C that speeds it up with native functions. The extension is compiled when you do ‘gem install nokogiri’ and will compile even though the vasprintf function is missing in your environment.

vasprintf is available in Linux, but not in Windows or Solaris. Nokogiri already have a workaround in place for Windows, but they don’t yet detect the issue in Solaris so the error still occurs. I plan to submit a patch to detect this automatically. If for any reason you need to get nokogiri working immediately on your Solaris 11-based Joyent accelerator, I did the following after installing the nokogiri gem:

cd /opt/local/lib/ruby/gems/1.8/gems/nokogiri-1.2.3/ext/nokogiri/
vi native.c
[remove the #if XP_WIN line and its corresponding #endif]
vi native.h
[remove the #if XP_WIN line and its corresponding #endif]
make install

FWIW, on Linux and Mac OS X nokogiri just works.

Posted in Rails | Leave a comment

Issues with JBCP and Sybase

BCP is a method for quickly copying data into SQL Server or Sybase databases. It’s much faster than running INSERT statements, so if you have a large amount of data, it’s a tempting option.

However, the trade-off for the speed is that when importing data, it bypasses a large amount of error checking and handling. As a result, any error messages you do get from the database server can often be cryptic or can even appear to be unrelated to what you’re trying to accomplish!

As well as the command-line BCP tool, JBCP is a pure Java library that reimplements the BCP protocol for Java developers. Unfortunately it’s still relatively immature, and you may find that Sybase gives the following error message in response to almost all JBCP issues:

Bad row data received from the client while bulk copying into object 1874356894 in database 4

This can be caused by several things. The most common is simply that the table definition has not been setup correctly to allow rows to be BCP’d into it. One way to resolve the issue is to ensure that the table you are copying into has ‘lock allpages’ as part of its definition, for example:

CREATE TABLE bcptest (some_key int not null, mydata varchar(50) null) lock allpages

Other issues can be caused by using univarchar columns that exceed 255 bytes. This means that all univarchar columns you attempt to copy into must be no larger than univarchar(127). A valid workaround for this issue is to split large column definitions into several smaller columns, and then use an UPDATE statement to reassemble the data from the split columns after it has been uploaded.

To help googlers, here is the complete stack trace I was typically seeing from JBCP before I created my table with the additional lock allpages clauses.

java.sql.SQLException: Bad row data received from the client while bulk
copying into object 1874356894 in database 4. Received a row of length
72 whilst maximum or expected row length is 15.
[19/12 10:46:37.160] [TID:lee2BCP1]:Upload of 1 result: FAILED
       at net.sourceforge.jtds.jdbc.TdsCore.tdsErrorToken(TdsCore.java:3149)
       at net.sourceforge.jtds.jdbc.TdsCore.nextToken(TdsCore.java:2587)
       at net.sourceforge.jtds.jdbc.TdsCore.getMoreResults(TdsCore.java:734)
       at net.sourceforge.jtds.jdbc.TdsCore.bcpBatch(TdsCore.java:2394)
       at net.sourceforge.jtds.jdbc.BCP.bcpBatch(BCP.java:1134)

One final warning for using JBCP – you don’t always even see the problem by default – some exceptions are supressed causing silent failure! There be dragons!

Posted in Java | 1 Comment

Getting Rails 2.2 to work on Mac OS X, despite the MySQL ruby “gem”

rubygems makes package management a nightmare. This is demonstrated every time you try and setup a new server using your operating system’s ruby/rails packages. It gets fully demonstrated when you try and upgrade to Rails 2.2 on a Mac. You can go read the full details of the nightmare if you’re so inclined.

The summary is that rails 2.2 removes the mysql driver and so you have to install a native driver using rubygems. Normally this would be a single command, but MySQL is a mess on Mac OS X. If you have a working MySQL installation on a Mac, chances are you’ve used MAMP and/or installed it yourself.

After about two hours of pain, I finally came across this forum post which has the horribly hacky but wonderfully simple idea of copying the mysql driver that worked in older versions of rails into your rails 2.2 app! This finally worked! On my Mac, this meant running the following command:

 cp /Library/Ruby/Gems/1.8/gems/activerecord-2.1.2/lib/active_record/vendor/mysql.rb ~/Software/myapp/lib/

When I restarted my rails app, it actually worked! Joy!

It’s worth noting that it’s probably worth pushing through the pain to install the native mysql gem on your production servers, but this technique is a winner to keep development on the go.

Posted in Rails | Leave a comment

Head Hunting; a brand new way to recruit top talent

I’m pleased to announce the first public beta release of an exciting new service from Crossbone Systems.

Head Hunting is a revolutionary new way to recruit employees at a fraction of the cost of other methods such as recruitment agencies and big job sites. As a Facebook application, Head Hunting allows you to hire new employees with a little help from your friends.

This week the service has launched into “public beta”, which means anyone can post and search job listings for free. Continue reading

Posted in Announcements, Starting up | Tagged , , , | 1 Comment

Fun with FBJS: “Can’t find variable: a43014453287_slider”

I’ve been trying to get a slider bar working recently as part of a facebook application. To get the example on the Facebook wiki working out-of-the-box was no problem.

The problems came when I wanted to create the slider bar as the result of a user clicking on an input. For some reason, Facebook only loads 3rd party Javascript (ie. mine) in the body of the page. If a user clicks a link that calls a Javascript function before the page has finished loading, the function may fail if it depends on functions kept in external Javascript files (that have not yet loaded). 

Because of the complexity of Facebook pages, there is often between 1 and 5 seconds when a user may click one of my links even though the page hasn’t technically finished loading. If this happens, the user will either see a very cryptic error or nothing will happen. It’s a completely unacceptable user experience so I was forced to come up with the workaround below.  

var sliderCreated = false; // can only create one slider per-page with this
function createSlider() {
    if (!sliderCreated) {
        try {
            new slider(document.getElementById('output'), document.getElementById('count_slider'), 0, 100000, 250, document.getElementById('salary_min'), , 500);
            sliderCreated = true;
        } catch (error) {
            // Errors may get thrown if the fbslider.js wasn't loaded quickly enough, so we wait a second
            setTimeout(function() { createSlider() }, 1000);

This will detect any errors thrown from the creation of the slider (which relies on an external Javascript file). If an error is found, then the attempt to create the slider will occur again after a second. This has the advantage that even if the second attempt fails (if the network is very slow), it will continue to retry with a delay between each attempt.

A variable (sliderCreated) is used to detect when the slider has been successfully created. In case the link that creates the slider is still clickable after the slider is created, this variable guards against multiple sliders being spawned on the page.

It is left as an exercise to the reader to add an upper limit to the retries if required.

Posted in General | Tagged ,

Effortless online VAT returns with KashFlow

Once you are registered for VAT, sending in your returns every three months can be a bit of a daunting task, especially if you’re not keeping strict electronic records on a regular basis.

I’ve blogged about various online accounting packages before, but if you want to keep track of your company’s finances, and make your VAT returns effortless, KashFlow is the way to go. Continue reading

Posted in HOW-TOs | Leave a comment

Explained: learning Ruby on Rails (Part 2)

If you followed along in , you will have downloaded and installed Netbeans 6 to get a complete Ruby development environment. You should also have prototyped a web design idea, added some dynamic code to it, and got cosy with Ruby by implementing a small standalone application.

In this article, we’ll learn a few more techniques to help you build the next big thing for the web. Continue reading

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