Images being requested twice from the server

Jonas Bush — Mon, 13 Jul 2009 16:55:59 GMT

*taptaptap* Is this thing on?

I ran into an interesting bug recently, where you would get 2 identical requests to the page you were visiting. I wasn't sure where this was coming from, so I poked around a bit. It turns out that having an <img /> tag on a page with an empty src attribute (like so: <img src="" />) causes that image tag to point to the containing page, causing the entire page to get requested again (causing any server-side code you may have to get executed again), but the response just gets thrown away, since the img tag is only expecting an image back from the server, not an HTML document.

The way around this is to remove the src attribute altogether, and you can still set the image source through javascript.

Retrieivng data from XML inside SQL

Jonas Bush — Wed, 03 May 2006 20:07:00 GMT

Recently I had to retrieve some data from SQL that was tucked away inside XML. We have a “Settings” class inside our application that is a bunch of public properties, which we then serialize to XML to store inside the DB. This lets us easily add/remove fields to store without having to modify the database.

This can be a problem if you need to access those one of those field values from within SQL, but SQL 2005 provides some methods to do this (note that your data column must be the xml data type, I haven't found a way to get this to work by casting an ntext field to xml):

Providing your class looks like this:

[XmlSerializable]
public class GlobalSettings
{
[XmlElement]
public int SomeValue;
}

Then when serialized, your XML will look similar to this:

In SQL Management studio, you can write this (assuming GlobalSettings is the table and GlobalSettingsXML is the column where this data is stored):

SELECT GlobalSettingsXML.query('(/GlobalSettings/SomeValue)') FROM GlobalSettings

This will return:

Which may not be as useful as we want. :) To get the actual value (5) from this, we need to use the value() function:

SELECT GlobalSettingsXML.value('(/GlobalSettings/SomeValue)[1]', 'int') FROM GlobalSettings

This will give us '5', cast to an int. Per the MSDN helps on value(), the [1] is required after your xpath expression because the expression is supposed to return a singleton. I'm not quite sure what that means or how the [1] denotes it, but it works (if you know, by all means tell me!).

Hopefully this will be of use to you.