This note is a reminder that there is something called AppArmor that could cause weird errors ("File not found", "Can...

Have a backup. Stop MySQL: sudo service mysql stop Move (or copy) your mysql directory. If you want /mnt/mysql to...

The code below shows a method #validate which uses Nokogiri to validate an XML document against an XSD schema. It...

A check if two date or time ranges A and B overlap needs to cover a lot of cases:

This might be due to AppArmor denying the MySQL server access to most of the filesystem. You can instead use...

There are times when you need to send SQL to the database, like this: def self.some_count(field) field = connection.quote...

This is for those who already own an SSL certificate (e.g. using it in the Apache HTTP Server) and need...

In regular expressions you can use the zero-width pattern \b to match the beginning or end of a word...

If you need to export data from MySQL to a CSV, you can profit from really fast built-in methods...

To clear the query cache in your MySQL database manually, e.g. for database profiling, execute the following command in your...

Deadlocks only occur if two transactions in separate threads compete for the same rows in the database. They usually (but...

If you need to do calculations inside the database and can not use Ruby objects you may run into problems...

Occasionally some complex query must be processed on the database because building thousands of Ruby objects is impracticable.

CONCAT('foo', 'bar', NULL) = NULL the NULL always wins in MySQL. If you would rather treat NULL as...

Sometimes you inherit a non Rails or non Rack based web app such as PHP, Perl, Java / JEE, etc. I...

Use this MySQL command to show further info about a table: SHOW CREATE TABLE tags; This will output a table...

If a controller action responds to other formats than HTML (XML, PDF, Excel, JSON, ...), you can reach that code in...

If you want to see how long your database queries actually take, you need to disable MySQL's query cache...

It can be useful to have a Ruby expression like condition ? positive_case : negative_case in MySQL queries:

When you need to delete rows from a table, and the delete conditions require a joined table, MySQL needs to...

For some reason you want to define a find condition in array form. And in that condition both column name...

This will show you how to create a RSS feed that the Feed Validator considers valid. Note that RSS is...

The ECB has an XML feed with EURO exchange rates to other currencies. It is updated daily.

Update RubyGems and Passenger Bundler requires Rubygems >= 1.3.6. Run gem update --system if you have an older version.