ADVANCED macromedia COLDFUSION MX 7 Application Development [Electronic resources] نسخه متنی

Anatomy of a WDDX Packet

Now that you have an idea about how the <cfwddx> tag works, let's take a closer look at the WDDX packets themselves. You've already seen WDDX packets as displayed in a browser (Figures 16.1 and 16.3), but packets aren't really meant to be displayed on Web pages. It makes more sense to look at them as if they were data files, kind of like a database or delimited text file.

Listing 16.1. I have added some carriage returns and indention to make the packet easier on the eyes. The whitespace I added doesn't make the packet any less valid, but it makes it easier for us humans to understand.

Listing 16.1

<wddxPacket version='1.0'>
<header/>
<data>
<string>Hello, World!</string>
</data>
</wddxPacket>

The entire packet is enclosed between a pair of <wddxPacket> tags. As of this writing, the version attribute will always be 1.0. If the WDDX specification changes in the future, the version number will be updated accordingly. This way, before an application attempts to deserialize a packet, it can check the version number to ensure that it knows how to read all the tags in the packet before it starts.

Listing 16.3). The same <wddxPacket>, <header>, and <data> elements are present and will always be present in any valid packet. Not surprisingly, this packet contains quite a few additional elements nested within its <data> block.

Again, I've added indention to make the packet more readable on the printed page, but the indention doesn't affect the validity of the packet.

Listing 16.3

<wddxPacket version='1.0'>
<header/>
<data>
<struct>
<var name='PACKETDATE'>
<dateTime>2002-6-16T14:51:5-5:0</dateTime>
</var>
<var name='FILMS'>
<recordset 
fieldNames='FILMID,MOVIETITLE,AMOUNTBUDGETED,DATEINTHEATERS'
rowCount='5'>
<field name='FILMID'>
<number>1.0</number>
<number>2.0</number>
<number>3.0</number>
<number>18.0</number>
<number>21.0</number>
</field>
<field name='MOVIETITLE'>
<string>Being Unbearably Light</string>
<string>Charlie's Devils</string>
<string>Closet Encounters of the Odd Kind</string>
<string>Folded Laundry, Concealed Ticket</string>
<string>Forrest Trump</string>
</field>
<field name='AMOUNTBUDGETED'>
<number>300000.0</number>
<number>750000.0</number>
<number>350000.0</number>
<number>7000000.0</number>
<number>1.35E8</number>
</field>
<field name='DATEINTHEATERS'>
<dateTime>2000-8-1T0:0:0-5:0</dateTime>
<dateTime>2000-12-25T0:0:0-5:0</dateTime>
<dateTime>2000-11-7T0:0:0-5:0</dateTime>
<dateTime>2002-9-15T0:0:0-5:0</dateTime>
<dateTime>2004-7-12T0:0:0-5:0</dateTime>
</field>
 </recordset>
</var>
<var name='COMPANYNAME'>
<string>Orange Whip Studios</string>
</var>
<var name='COMPANYURL'>
<string>http://www.orangewhipstudios.com</string>
</var>
<var name='OFFICES'>
<array length='3'>
<string>New York, NY</string>
<string>Paris, France</string>
<string>Pittsfield, MA</string>
</array>
</var>
</struct>
</data>
</wddxPacket>

Tables 16.2 and 16.3 provide a brief explanation of the various XML elements and attributes found in WDDX packets. Basically, the idea is to define the basic types of information that can be stored in packets (see Table 16.2), and then allow these types to be arranged as complex structures that mimic arrays, structures (or associative arrays), or recordsets (see Table 16.3). The result is a system that allows just about any type of information typically tracked by applications, regardless of the programming language used, to be represented cleanly and clearly.

NOTE

In general, you never have to actually type the tags in