Archive for November, 2004

Reinitializing an Application Using Blackstone Events

One of the most useful tags I’ve ever written is the init tag. Typically, it goes
in your Application.cfm file, and the body of the tag gets executed only the first
time it’s encountered, which means it’s the perfect place to put initialization
code. You can also force the body to execute again by passing a certain query string
parameter in with any request. This is very useful during development when you need
to flush cached components or other data.

As I started thinking more in Blackstone terms, however, I wondered what the Blackstone
equivalent on the init tag would be. Of course, the init tag still works in Blackstone
as does all the CFMX 6.1 code I’ve run so far, but I wanted to take advantage of
the new event handling
mechanisms available in Blackstone
. So here’s what I’ve come
up with so far.

Now, I handle application initialization using the onApplicationStart event. That
takes care of running the code only once (usually when the application receives
its first request since the server was last started). I then added the following
inside my onRequestStart event handler:

<!--- Re-initialize the application, if necessary --->
<cfif structKeyExists(url, "restart") and url.restart>
<!--- Invoke onApplicationStart event --->
</cfif>

Now, when I want to invoke the onApplicationStart event, I just append a restart=true
parameter to any request, and my application is reinitialized without me having
to restart the server.

Google’s Been Busy

  1. Google acquires Keyhole:

    Keyhole is the 3D digital earth pioneer—the only company to deliver a
    3D digital model of the entire earth via the Internet. Keyhole’s groundbreaking
    EarthStream™ technology combines advanced 3D graphics and network streaming
    innovations to produce a high performance system that runs on standard PC’s
    and commodity servers. Both high performance and intuitive to use, Keyhole’s
    solutions enable anyone to manipulate a rich map of the earth composed of imagery
    and feature information.

  2. Google launches Google Scholar (beta,
    naturally):

    Google Scholar enables you to search specifically for scholarly literature,
    including peer-reviewed papers, theses, books, preprints, abstracts and technical
    reports from all broad areas of research. Use Google Scholar to find articles
    from a wide variety of academic publishers, professional societies, preprint repositories
    and universities, as well as scholarly articles available across the web.

Chopping Off the End of a List

I’m sure there are tons of these functions around, but I decided to write my own.
The listChop function chops a list down to the specified size. Use it like this:

<cfset myList = "a,b,c,d,e"/>
<!--- Chop this list down to 3 elements. --->
<cfset myList = listChop(myList, 3[, delimiter])/>

Here’s the function:

<cffunction name="listChop" returnType="string" output="no" >
<cfargument name="targetList" type="string" required="true"/>
<cfargument name="amountToKeep" type="numeric" required="true"/>
<cfargument name="delimiter" type="string" required="false" default=","/>
<cfset var listSize = listLen(arguments.targetList, arguments.delimiter)/>
<cfset var i = 0/>
<cfif arguments.amountToKeep lt 0 or listSize - arguments.amountToKeep le 0>
<cfreturn arguments.targetList/>
</cfif>
<cfloop from="#arguments.amountToKeep+1#" to="#listSize#" index="i">
<cfset arguments.targetList = listDeleteAt(arguments.targetList,
arguments.amountToKeep+1,
arguments.delimiter)/>
</cfloop>
<cfreturn arguments.targetList/>
</cffunction>

I’m using it in a pretty big application I’m writing, so let me know if you see
any bugs.

Safely Selecting the Last Inserted ID, Part II

Well, as it turns out, this isn’t
an issue at all. I ran two tests. The first followed these steps:

  1. Using a CFQUERY tag, I executed an insert statement.
  2. Used Thread.sleep() to make the page hang for 10 seconds.
  3. Inserted ten additional rows from the command line (using the MySQL command
    line tool).
  4. After the Thread.sleep(), used LAST_INSERT_ID() to get the last inserted ID,
    and displaed it.

I expected the result to be 11, but it was actually 1.  The 10 rows I inserted
between the initial insert and when I selected the last inserted ID had no effect.  I
figured this was because ColdFusion was considered one client, and the command
line administrator was considered a different client, and since the scope of
the last inserted ID is the client/connection, I was protected.  So I ran this
test, instead:

  1. Executed an insert statement in ColdFusion.
  2. Slept for 10 seconds.
  3. Ran a second CFM page that inserted 10 rows while the first page was hung.
  4. After the thread in the original page woke up, selected the last inserted id
    and displayed it.

Keep in mind I was using no transactions or locks since I was trying to get a
wrong result before trying to figure out how to get the correct one, however
the result was once again 1.  As it turns out, no transactions or locks are
needed.  Why?  Apparently because each request gets its own database connection,
and that one connection gets reused for the duration for the request, regardless
of how many database operations you perform.  Other
requests can happen simultanously, of course, but they all get their own connections,
and hense do not affect the first connection’s last inserted ID value.  In
other words, it seems to work exactly how you would want it to!  ColdFusion
does it again!

Disclaimer: This test was run using JRun, CFMX 6.1 (with the
latest updater) and MySQL
version 4.0.18.  Before you rely on this data, you might want to run some tests
yourself, though I will try to get confirmation from the ColdFusion team that
this technique should work across all databases and future versions of ColdFusion.

Safely Selecting the Last Inserted ID

I run into this issue occasionally, and always find some kind of work-around,
but I’ve finally decided to address it head-on. The scenario is this:

  1. You insert
    a record into the database.
  2. You need the ID of the row you just inserted so you can insert additional
    rows in other tables referencing the first row you inserted.
  3. You’re worried about your code being thread-safe, so you consider
    using locks, transactions, UUIDs, etc. But what is the best way?

The easiest and most database-independent way of doing this is to generate a UUID
and use it for the primary key for the first insert, and the foreign key for any
subsequent inserts. That’s fine for certain apps, but for the app I’m working on
now, I need to use sequential, auto incremented integers as keys. I’m using the
MySQL function LAST_INSERT_ID() to get the last inserted ID, however the ID’s scope
is the current connection, so if I use two CFQUERY tags (one to insert the row,
and one to get the last inserted ID), I believe it’s possible I could get the wrong
ID if another row is inserted between the time I do my insert and the time I select
the last inserted ID. So I’m going to try:

  1. Sending two queries to MySQL at the same time. One to do the insert, and one
    to do the select. Both statements will use the same connection, and problem
    solved. I haven’t had any luck with this so far, though. I’m not sure MySQL supports
    this as I keep getting SQL syntax errors.
  2. Putting both CFQUERY tags in a transaction (they actually already are in a
    transaction), and using the isolation level of serializable. I’m potentially
    sacrificing some performance, but it should be miniscule. This is a very
    good solution if it works, but I’m not 100% positive that it will work, though
    I am hopeful.
  3. Using an exclusive lock. If all else fails, this will definitely work, although
    the disadvantage is that I will only be taking database operations that
    originate from one CF server into account. In other words, another server that
    is unaffected by the lock can slip a new row into the database at just the right
    moment and trip me up. I would much rather the lock occur at a lower level — actually
    in the database, if possible.

I’ll post my results. In the meantime, anyone have any additional insight?

RSS All Over Macromedia.com

I’m sure you already knew about the Macromedia product RSS feeds, but did you know that forum posts are now available via RSS now, too? Just look for the “rss feed” link at the top of any Macromedia support forum.

Three New Macromedia Product RSS Feeds

Captivate, Flex Builder and RoboHelp have been added to the Macromedia Product RSS Feeds. If you’re not already using these feeds, you should be! If you’re new to RSS, you can find all the information you need to get started at the aforementioned link.

Official Macromedia MAX Coverage

Official Macromedia MAX coverage here. Specifically, coverage of the Day One General Session (with pictures).

Free Timbuk2 Macromedia Flash Bag

First person to find me at MAX and tell me they saw this post on MAXBloggers gets a very nice red Macromedia Flash Timbuk2 laptop bag (about a $100 value).

MAX Update: Keynote

I’m not going to get into specifics since Mike Chambers and Kevin Lynch have blogged most of the details, but I will say that it was a very good keynote, and an excellent crowd. The ColdFusion stuff was great. If you’ve seen or spoken to Ben Forta in the last few months, you’ve seen the Flash forms stuff he showed this morning, but I don’t think anyone has seen any of the SMS functionality yet. At the beginning of the keynote, we did a mock presidential election via SMS, then later created a Flash, FlashPaper, and PDF report out of the results, all with ColdFusion. (Yes, SMS functionality, built into Blackstone.)

I also really liked the Flash Player 8 (Maelstrom) demo that Mike Downey did. Basically, the next version of the Flash player is going to emphasize performance, expressiveness, and development standardization, although that description doesn’t even come close to doing it justice. What that translates into is that the next Flash Player will be very fast and extremely slick, and in my opinion, the most important and impressive version yet. Kevin Lynch helped put it into perspective by saying that we are putting more engineering effort into Maelstrom than all the previous versions of the Flash Player combined.

Check out Kevin’s and Mike’s posts for more info.