Peter Mac And Associates

Installing MySQL gem on OSX 10.6

Hopefully this will be a time saver for anyone else who goes through the following pain.

I have a brand spanking new OSX 10.6 installation.
I installed mysql 5.5.9-OSX10.6-X86 (because I thought everything was still i386 based…watch this space!)
I installed RVM and installed ruby 1.92 under RVM control.
I then do a ‘bundle install’ and it gripes about not having mysql2 gem installed. I do a manual install using the following command.

and after a bit of crunching, we get to the following error:

The Solution

Uninstall your MySQL using the commands below

Now go and download the 64 bit version of the MySQL package – get the dmg rather than the gzip file.

The rationale behind this is that your new beaut 10.6 is actually referencing 64 bit modules by default. How to prove this I do not know – I’m confused and still searching for the answer. If I do a uname – a I get…

Now, if I’m not mistaken that’s an i386 at the end – go figure. If anyone has any further insights please let me know.

The next step is to download the gem for your ruby/rails use

The next error encountered is when I try to start the rails server using ‘rails s’

The answer to this problem is to run the following command…

Bear in mind, I’m running version 1.9.2-p180 fo ruby – you will need to change the command for whatever version you’re running.

Setup Git Local and Remote Repositories

If you are a remote worker or, like me get some work done on the train on the way to/from your office, you’ll appreciate the need for set up of a local and remote source code repository, This allows you to develop using your laptop/netbook, check in your changes locally and when you arrive at the mothership later, you can synchronise your local repository with the remote one ensuring all your changes are available for other developers. This article shows how to set up git for both a mothership type repository (let’s call it the remote repository) and a local version on your own laptop.

Configuring Git project on the mothership.

Prerequisites:

A Git server (the mothership) has been set up on a box called bluelight. This box is available to the network as git.petermac.com.

A git user has been created on the server called ‘git’. This user has access to the folder where the git repositories are stored.

The Steps:

1.On your dev machine create your code project using whatever tools you need.

2.Initialise this working project under the git version control system

3.Add whatever work you’ve done to the repository

4.Check the files you want added have been added

5.Open a SSH session to bluelight – (the central git repository server)

6.Obviously substitute your real projectname and don’t forget to leave the .git extenstion

7.Initialise the repository under the new folder

8.Change ownership of the repository to the system git user

Configure git on your laptop to use the remote repository

1. Return back to the local machine and add reference to the new ‘remote’ repository from the base directory of the project.

2. Here the ‘git remote add’ part says add a reference to a remote repository. The second ‘remote’ is the friendly name I want to use when referring to the repository on the git server

3. Now commit the local files to the local repository – Note: Step 3 was only an add, not a commit. When you commit you’ll be prompted (or you can enter it as a -m option) to enter a message to be used as a comment.

4. It’s time to test the new remote repository by ‘pushing your local repository info up to it. This is done using git push

Didn’t quite go to plan – so let’s see what’s wrong

let’s try again

looks like it will work so remove the dry-run parameter

That’s all folks!

Rails 3, jQuery and multiselect dependencies part 2.

This article is a follow up to another article on this website which focuses on using jQuery to manage the processing of multiple inter-dependent select lists on a single web page. I had a number of requests to explain the data model in a bit more detail so here goes.

I have worked on a number of internationalised (in the US, that’s spelt internationalized) applications where the selection of a ‘home country’ by a user means the display of their address fields should change to reflect their selection of a country. I’ve used this example as the basis of the multi-select article.

MySQL Data Structure

The relevant tables are in a MySQL database and are as follows:

• locales
• countries
• countrynames
• regionnames
• regions
• cities
• citynames
• users

The structure of each of the tables is as follows. Note, this is by no means a strict design criteria for your tables, it’s just a design decision that I made because it made sense to me and my warped view of the world.

The locales table contains a listing of a possible 29 locales that can be used to tailor how your application displays and interprets data

The countries table contains core country information including their names in English, their international code and their latitude and longitude.

The countrynames table contains the names of countries as it is interpreted in each locale. For example the country Andorra is the same in most locales ‘Andorra’ but in Russian it is ‘Андорра’.

Now we’re into the messy bit. If you live in the United States, well it’s like it says on the box…it’s united ‘States’; however if you live in the United Kingdom it’s all about counties. If like me you live in Australia, we have both States and Territories (it’s a long story..look up the difference on google). Regardless of the type of country divisions, the name I’ve used is ‘Region’.

The regions table defines the region names within countries.

The localised version of the regions table is regionnames.

Next is the cities within the regions and their localised versions. These use the tables ‘cities’ and ‘citynames’ respectively. You can see the foreign key link to the country and region tables below.

The cities table

The citynames table holds the localised version of city names.

There are other tables in the system including a users’ table with a locale_id which the user sets by selecting from a drop-down list on their profile-page. I haven’t included that table her because there’s also a bundle of application specific stuff in there too.

The Rails Schema

Now, like all good rails developers, you’re using schema migrations. If you’re not, go stand in the corner for twenty minutes and think about spending the same twenty minutes every week wasted looking at the conjoin between two walls. Rails database migrations are the way to go. They take a little bit of getting used to but well worth it to keep all your team on the same page, or if you’re doing your bit as a solo programmer it means you can screw it up and rewind to the last working version with ease.

As an example, I’ll show you how to create a new schema file for the cities entity. I’ll leave the remaining entities for your own interpretation.

In Rails 2, you’d use the following line

In Rails 3, it’s more DRY

This will create a new file in you db/migrate folder ending in ‘create cities.rb’. Edit this accordingly and add the fields to the migration that reflect the structure of the table we want to create. My version looks like the following:

The Models

In the root of your application, create the necessary models. Under Rails 3, that can be done by entering

A new file is generated under the app/models folder called city.rb.

The full listing of my models folder is as follows:

For the purposes of this discussion we’re interested in everything but the last 4 files. These are used to store user permissions, roles, and profile data.

The content of the relevant model files is used to implement the relationships between the different entities and some field level validation rules. There is nothing whiz-bang about this, just the use of the Rails convention over configuration principle at work.

Taking it from the top, my files look like the following:

So, there you have it, fairly simple really, a couple of tables, a couple of model files and the material from this article and the previous article should have you up and running. As always, any queries, comments or improvements, please let me know.

Scaling images in batch mode

I have lots of folders with images uploaded from digital cameras. Average image size is 3MB which is way too large for uploading to web based image sites. What I need to do is to rescale the images but doing them one at a time is a pain so I wrote a little script to do them one folder at a time.

The script makes use of a program called ‘convert’. This is part of the ImageMagick suite of tools.

Install ImageMagick

Once installed try to verify the location of the convert program

The way the script works is to create a new folder called ‘resized’ under the folder you want to process. It then places rescaled versions of the images it finds in the source folder.

The scaling is performed by passing a width x height parameter to the convert program. The question is how do you know what value to provide without screwing up the ratio of your image. What I do is open a sample image in Gimp. Go to the ‘Image|Scale’ menu option. I pick a value for the width, hit tab and it provides you with the correct value for the height. This is fine if all your images are of the same size. You’ll have to put in a bit of work if they are different sizes.

Here’s the script..it’s really simple as you can see, but I had an itch and I had to scratch it.

Save the script as image_resize.sh. Do a chmod a+x so you can execute it. Then create a sample folder with a few images copied just for testing. Run it as follows:

That’s all folks!

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Purrfect Java Solutions

Meet “Java”, a new addition to the PeterMac team.

Although only 9 weeks old, she shows great focus in object oriented design (she chases any object that moves). She’s got an excellent grasp of string manipulation technniques and we have to agree that her display of experience in the J2SE (Sleeping and Eating) area is beyond expectations for one so young.