Do you want answers to questions like:

• What do you think about the current Twitter vs DHH discussion?
• How did you come by with the Magic Model solution?
• What does the New Gem Generator actually do?
• Will we see ‘Rails Distros’ in the long run?
• Where are you from? What’s your current day job, is it Rails related? And what’s your history with Rails?
• Did you get your free t-shirt?

Brazilian Fabio Akita - author of the first Brazilian book on Ruby on Rails also wanted to know, so he asked.

Thanks to my friend Carlos Eduardo for teeing it up.

Go to interview

Over the last few months, we at Dr Nic Magic Models (Sweden) Inc. have been gradually selling down all the company shares to pension funds at over-inflated prices, whilst at the same time refusing to release new patches for old projects that sorely need them - Composite Primary Keys and Dr Nic’s Magic Models.

Magic Models 0.8.0 exhibited range of wacky behaviour and I’ve been suggesting people 0.7.2 for a long time, instead of releasing 0.9.0, which I mostly wrote last year.

I received a huge patch for Composite Primary Keys in my inbox in February and despite the emails of “when will this patch be released” by the punters, I sat on it.

I’ve also mentioned in emails several new projects that I’ve either never released or they are lurking on RubyForge without any celebratory fanfare. For example, the Magic Model Generator - got 200 tables in a legacy schema? Generate 200 model files in 20 seconds.

The share price has now plummeted, and over Easter I bought back all the shares at half price. All that’s left to do now is unveil a barrage of new projects and releases and watch the share price soar. Booya.

So, over the next week or so, you will be treated to:

So call the babysitter, grab yourself a champagne, and find a seat in front of the catwalk: its show time.

I wrote Composite Primary Keys and Dr Nic’s Magic Models because we have a 50+ table legacy database and I am terrorised by explicit SQL statements on a daily basis. I have a dirty secret - I don’t use either of them at work. We’ve been unsuccessful installing Ruby on our HP-UX box, then time passed, life moved on for the people involved, and so no Ruby. Ergo, SQL hell for Nicholas.

Until today. No, we still don’t have Ruby installed on our HP box, but I do have it installed everywhere else in my life. So I guess I can still access the database remotely… that’s what the TCP/IP internet protocol is for… and for executing shell commands why not remote shell into the box?

Let’s skip over why I never thought of either of these until now. Its bad for my ego. The upside of this minor revelation is that the Composite Primary Keys project will have Oracle support soon.

Remote Shell

The point of this article though is to discuss the wonders of using remote ssh (aka remote shell) to invoke shell commands via ruby without having ruby installed locally.

I made it work, it rocks and I shall briefly sing the praises for Jamis Buck. Jamis, you rock. net-ssh is a lovely API for performing remote shell commands all from ruby. Here’s a demo of what I can do (excluding the setup code which is discussed later):

>> print shell.pwd.stdout
/home/senwilli
>> shell.cd 'demo'
=> #<struct Net::SSH::Service::Shell::SyncShell::CommandOutput stdout="", stderr=nil, status=0>
>> out = shell.ls '-lart'; print out.stdout
total 16
drwxr-xr-x   2 senwilli   sv              96 Sep 22 11:56 .
drwxr-xr-x   5 senwilli   sv            8192 Sep 22 11:56 ..
>> out = shell.send_command 'ls -lart'; print out.stdout
total 16
drwxr-xr-x   2 senwilli   sv              96 Sep 22 11:56 .
drwxr-xr-x   5 senwilli   sv            8192 Sep 22 11:56 ..

I’ve deliberately been inconsistent in the way I called the shell commands and how I handled the responses to show you some interesting things.

shell is our shell object (which we’ll cover in a bit) and it has delightfully overridden method_missing so I can send it any old shell command I like. In the example above, I call the commands: pwd, cd and ls using this method. The first parameter is the arguments you’d like to pass to the command. An optional second parameter is for any stdin you’d like to pass to the process during its execution.

The last command is a duplicate of the previous command, showing that you can explicitly pass a complete shell expression string via the send_command method.

The result of all shell commands is a struct containing stdout and stderr strings. So, to return the response of the command to the user or logger, you’ll need to store the response object (as per the out variable above) and use stdout? to test if stdout has anything in it.

In the example above, all these commands are executedly being executed synchronously, so I’m getting the stdout/stderr results back before the next command is executed. This is due to the way I created the Shell object. So, let’s look at that.

Creating your Shell object

First you’ll need to install the following gems (from rubyforge.org) in this order: needle, oepnssl, and net-ssh.

In your ruby script/console:

require 'net/ssh'

session = Net::SSH.start( 'host', 'user', 'passwd' )

To create our synchronous shell:

shell = session.shell.sync

And you’re off and racing.

Jamis has provided lots of useful syntatic sugar (for example, you can pass Net::SSH.start a block with session as its argument, and reading all the docco is a clever thing to do next.

Using sudo?

The only thing I couldn’t immediately figure out is how to invoke sudo su - envname and then continue to control my shell as per normal. All commands just blocked.

Luckily there is a mailing list for me to loiter in…

The good people at Err-the-Blog were almost satisfied with the humble offerings of Composite Primary Keys, which provide composite key support for ActiveRecords, including composite foreign keys in assocations. They’ve gone on an published the main remaining requested feature - composite migrations for your database table changes.

Errtheblog - Composite Migrations

Now, this means that if you want to use composite foreign keys because you like them you can create as many as you like and DHH can’t make it hard for you.

Thanks to the fine work of Santiago on the forum, some sneaky defects have been found. The new release is now up on rubyforge and available via gem install composite_primary_keys.

Thanks to everyone for helping each other solve the “ActiveRecord hates Composite Primary Keys” legacy.

Bonus thought: Who wants to generate composite primary keys in their migrations?