Computer Information Technology Notes: 2009

Tuesday, December 29, 2009

Enum as a class property in Objective-C

For this post I'd like to show how you can define an enum property in Objective-C.

In a nutshell an enum is a datatype you create where in theory only certain values can be assigned to it and none else.

The code is pretty straight forward. Here it goes:

typedef enum

{

North, South, East, West

} Direction;

@interface MyClassName : NSObject

{

Direction direction;

}

@property(nonatomic) Direction direction;

In the above example only the values North, South, East, and West can be assigned to the direction property of a MyClassName instance.

Tuesday, December 8, 2009

Querying an Oracle database using XSLT for dummies

In this post I will explain how you can query an Oracle database using XSLT technology and Xalan as your XML processor.

Requirements:

Oracle 10g (or above)
Oxygen (XML Editor)

If you decide that you don't want to use an XML editor you will have to download Xalan and add the necessary libraries to your classpath before processing the XSLT file. If you decide to take that route you can follow the first steps in this tutorial, which explains how to setup your environment without an XML editor.

Tutorial

1. Open Oxygen and create a new document of type XSLT

2. Copy and paste the XSLT code below:
<?xml version="1.0"?>
<xsl:stylesheet version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
xmlns:sql="org.apache.xalan.lib.sql.XConnection"
extension-element-prefixes="sql">
<xsl:output method="html" />
<xsl:template match="/">
<xsl:variable
name="movies"
select="sql:new('oracle.jdbc.driver.OracleDriver'
,'jdbc:oracle:thin:@ipaddress:sid','username','password')" />
<xsl:variable name="streaming" select="sql:disableStreamingMode($movies)" />
<xsl:variable
name="queryResults"
select="sql:query($movies,'SELECT movie, actor FROM movie')" />
<html>
<head><title>Oracle Result Set</title></head>
<body style="font-family: sans-serif;">
<table border="1" cellpadding="5">
<tr>
<xsl:for-each select="$queryResults/sql/metadata/column-header">
<th><xsl:value-of select="@column-label" /></th>
</xsl:for-each>
</tr>
<xsl:apply-templates select="$queryResults/sql/row-set/row" />
</table>
</body>
</html>
<xsl:value-of select="sql:close($movies)" />
</xsl:template>
<xsl:template match="row">
<tr><xsl:apply-templates select="col" /></tr>
</xsl:template>
<xsl:template match="col">
<td><xsl:value-of select="text()" /></td>
</xsl:template>
</xsl:stylesheet>
3. Be sure to make your changes accordingly
4. After pasting your code in the text area click on the XSLT debugger button as shown in the image below:

5. Click on the Run button

6. Voilà! Now look at the result, and here is what I got from my XSLT:

MOVIE	ACTOR
Indiana Jones and the Last Crusade	Alison Doody
Indiana Jones and Raiders of the Lost Ark	Harrison Ford
Indiana Jones and Raiders of the Lost Ark	Denholm Elliott
Indiana Jones and the Last Crusade	Sean Connery
Indiana Jones and Raiders of the Lost Ark	Jonn Rhys-Davies

Friday, February 27, 2009

Turning off the PC Speaker on Ubuntu

Here is how you turn off the PC Speaker on Ubuntu. This command migh even work with other Linux distros.

modprobe -r pcspkr

Friday, February 6, 2009

Deleting files/folders with the same name characteristics in Linux

I was trying to delete the .svn folders from a project in my linux machine and I had two options of doing that. Going folder by folder and find those .svn folders, which were about 20 or delete them all with one line of command connected by a pipe "|".

Here goes the trick and the explanation will follow it.

find /path/projectFolder -type d -name '.svn' | xargs rm -rf

Notice that we start this batch of commands with the find command. The find command takes 3 arguments. The find command will go through all directories and subdirectories starting from the path specified.

The first argument is the path to the folder where you want to perform the lookup of the file/folder. That's pretty straight forward

The second argument is the option "-type" where you define whether you are looking up a file or a directory. In the example given above I defined the type as being a directory. If I wanted to do a lookup for a file I would have an "f" there rather than a "d".

The third argument is the option "-name" where you define the name of the file or folder you want to look for enclosed by single quotes. You can also use wildcards in the name.

The second command I want to talk about is the rm -rf. This command removes all folders that are empty or has something in it.

Now here comes the trick. Every line that the find command returns is passed in to rm -rf through | xargs.
Now, having that in mind if you read from right to left this line commands should make more sense to you.

Google the commands find and xargs to see some cool stuff that you can do with them.

Hope this helps!

Computer Information Technology Notes