The best programmers are not marginally better than merely good ones. They are an order-of-magnitude better, measured by whatever standard: conceptual creativity, speed, ingenuity of design, or problem-solving ability.

— Randall E. Stross

I’ve been writing billing system code for years, but this is something I’ve not known until today: VISA, MasterCard and American Express credit card numbers can be checked for validity (meaning you gain one extra check against someone typing in random numbers) using what’s known as the Luhn algorithm.

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Anyone who’s tried to install the Rails gem Devise on their Windows PC know that it’s not a smooth process – it takes a bit of massaging, requiring use of a development kit from the RubyInstaller For Windows website and a special parameter to be passed to the gem executable.

1. Grab the latest version of the development kit, DevKit-4.5.0-20100819-1536-sfx.exe, from the RubyInstaller Downloads page.
2. Run the self-extracting installer, placing all files to C:\devkit\ . Navigate to the directory and initialize the development kit by executing:

   ruby dk.rb init

3. Review the auto-recognized paths to ensure its accuracy:

   ruby dk.rb review

4. Finally, actually install the development kit add-ons:

   ruby dk.rb install

5. Now we’re ready to install our problematic gems! In the same directory, execute your gem command:

   gem install devise --platform=ruby

You’ll note the include of the flag –platform=ruby in the last command listed above – it’s essential in avoiding a make issue inherent to the Windows environment. Also, bcrypt-ruby is installed as a requirement of the devise gem, so that’s two birds with one stone if you’re looking to make use of both. Enjoy!

References:

• Stack Overflow: Installing bcrypt-ruby gem on Windows
• base.extend: Devise with Ruby 1.9.2, Rails 3 and Windows

Here’s a one-line command that bypasses the necessity of the COPY privilege in being able to output data in comma-separated value (CSV) format:

psql -U username -h 127.0.0.1 -W database -F ',' -t -A -c 'SELECT * FROM Users' -o outputfile.csv

Also useful is taking input from a file (which helps avoid issues with quote characters):

psql -U username -h 127.0.0.1 -W database -F ',' -t -A -f input.sql -o outputfile.csv

You’re probably already familiar with most of these options, but the less common ones are:

• -F changes the field separator to the , character
• -t outputs the rows without their column names (which seems to undo the use of -F)
• -A un-centers the row output
• -c contains the actual query you wish to run
• -f takes input of the query you wish to run from a file
• -o redirects the output of the query to the specified file

While setting up my laptop to do development work on I came to the realization that I’ve always gotten my IDE running using a patchwork quilt of websites, each providing small but crucial tips on getting a Rails dev environment with GitHub integration working smoothly under Windows. Here’s my attempt to put all those tips in an ordered list for others to benefit from.inflatables for sale in canada

This guide assumes you’ve already created yourself a GitHub account, so if you haven’t gotten to that yet, head on over and spend the two minutes it takes to register and verify an account.

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Found the article Locating the node by value containing whitespaces using XPath on Stack Overflow – reprinted here so I don’t forget it:

If you know the exact value of the node – say it’s “Hello World” with a space used jumpers for sale:

<top>
   <aChild>Hello World</aChild>
</top>

Then the XPath expression:

/top/aChild[.='Hello World']

will select this node.

Found this a few minutes ago and already lost the source URL. With PostgreSQL requiring you to add data manipulation privileges on a table-by-table basis, it’s handy to have a method to spit out a list of GRANT commands to run when you want to give a user a privilege across the entire database.

SELECT 'GRANT SELECT ON '||schemaname||'.'||tablename||' TO fillinusername;' 
FROM pg_tables 
WHERE schemaname IN ('fillindatabasename', 'fillinschema') 
ORDER BY schemaname, tablename; 

In the above, you need to change:

• fillinusername: The username you wish to grant privileges to.
• fillindatabasename: The database within which you will be granting table privileges upon.
• fillinschema: The schema the tables are contained within (usually “public”).

This will spit out a list like:

                                  ?column?
-----------------------------------------------------------------------------
 GRANT SELECT ON fillinschema.table1 TO fillinusername;
 GRANT SELECT ON fillinschema.table2 TO fillinusername;
 GRANT SELECT ON fillinschema.table3 TO fillinusername;
 GRANT SELECT ON fillinschema.table4 TO fillinusername;
 GRANT SELECT ON fillinschema.table5 TO fillinusername;
 ...

Copy and paste that list back into PostgreSQL to execute the GRANT commands to get your user privileges set up. (If it’s a large list, output the command to a file and run them that way.)