Sunday, August 28, 2011

Open/Closed Principle: Delegate Example

In object-oriented programming, the open/closed principle is a very important principle. Software entities (classes, modules, functions, etc.) should be open for extension, but closed for modification. Recently I tried to summary some commonly used components in a serials of documents. I found that I have used delegate in my LogHelper class. This reminds me about my OCP.

I was not intended to use delegate as a way to extend my log feature. I was using it to avoid building a message string but not actually used for logging. I thought it will be nice to use a pointer to function which returns a string. So that the function would be called dynamically only if logging is enabled.

public delegate string GetMessage();

public static class LogHelper {

public void WriteMessage(
ILog log, string flag, GetMessage getMessage)
if (log != null && getMessage != null
&& log.IsLogSet(flag))
var msg = getMessage();

Here is an example of the usage:

LogHelper.WriteMessage(log, "d", delegate() {
return string.format("MyObject: {0}",

As shown in above example, user can build a simple or complicated string for logging. Since the building codes are in a dynamic delegate. The delegate will only be called when the log flag "d" is enabled.

I think that my design of LogHelp class is a typical way to OCP. Here is another example to use the same method to enable indention and un-indention for messages:

class DataProcess {
private int m_indention = 0;

private void LogMsg(bool indent, GetMessage getMsg)
if ( getMsg == null )

if (indent)
m_indention+= 2;
else if ( m_indention > 0 )
m_indention -= 2;
m_indention = 0;

LogHelper.WriteMessage(log, "d", delegate() {
return string.format("{0}MyObject: {1}",
new String(' ', m_indention),


Sunday, August 21, 2011

Create Materialized View

This blog is about how to create a materialized view in SQL server database. By creating a materialized view, you can dramatically improve query performance. I learned this by my experience. Here are some key notes about the process.

Create a View

The first step you have to create a view. The first requirement for materialized view in SQL server is that a special WITH SCHEMABINDING has to be used for the view.
SELECT rawid,
FROM dbo.myRawDataTable
AND ( Isnumeric(VALUE) = 1 )
AND Name LIKE '%my_pattern%'

The second requirement is to make sure there are any keys in the view. For example, you can include key column or combination of columns as a unique identifier. This key will be used to create INDEX for the view.

Add a Index

The materialized view actually holds a block of data with Index. This makes view fast for retrieving data. For example, for above view, a INDEX is created:

-- Create UNIQUE CLUSTERED index on the view
ON [vMyView] (rowid, name, readingdate)

The Index is created depending on your query. With this Index, you will see great performance improvement, specially again huge amount of data.

Use (NOEXPAND) in SQL Query

With above preparation, the view is ready for use. However, I noticed that a special option has to be used in SQL query in order to take advantage of the Indexed view, for example:


This NOEXPAND has to be used in SQL Standard Server. In SQL Enterprise Edition Server, this is not required (but you have to pay big bucks).


Materialized View can improve SQL query performance dramatically, just like adding property Index to tables. The disadvantage is that the MV will take some disk spaces. You have to balance the weight in your real cases.


Sunday, August 14, 2011

Finished Watching WWDC 2011 Videos

Today I finished watching all the WWDC 2011 videos. I spent most of after-work hours to watch those shows. It is good to get an overall view of all the technologies used in iOS 5, even some I may not use at all and some are hard to digest.

I also started to write my notes in Chinese about WWDC 2011 shows. However, the notes are far more behind my watching schedule. I could not keep up my notes with my watching progress, and eventually I decided to left go behind. Right now my notes are close to the end of 100 serials. They are still 200, 400 and 500 serials to be written. I think it is good review when I write notes, and I'll keep it up to the end.


Monday, August 01, 2011

Updated to Xcode 4.1

Today I updated me Xcode to 4.1. It is a free version available from Apple store. That means you either have to have Snow Leopard or Lion if you want to get it. Before Lion's release it was $5.00 from Apple Store. I have not started my iOS development for a while since I have been kept watching WWDC 2011 videos. Right now I am in the half way through 400 sessions and only 500 serials in my schedule. It is really good to learn OS and iOS new features from those session videos.

The update of Xcode is 3GB+, almost as big as Lion. After the installation the Install Xcode app stays in Applications folder. I removed it from there after the installation (I made a copy of this package to my external HD). The following is the welcome window.

I'll have to squeeze time to go back to my development.