Net.Data Programming Guide

Using Large Objects

DB2 supports large objects (LOBs) on an increasing number of platforms. Check your DB2 documentation to see if it supports LOBs. The three types of LOBs DB2 supports are:

• Binary large objects (BLOBs)

• Character large objects (CLOBs)

• Double-byte large objects (DBLOBs)

When a query returns a LOB, Net.Data saves it in the directory specified by the HTML_PATH configuration variable. Consider system limitations when using LOBs because they can quickly consume resources. Some LOBs, like audio files, require special hardware and software.

LOBs generally contain a file signature in the first few bytes to indicate what type of information the file contains. If a LOB is recognized by Net.Data, the extension is added to the temporary file and to the Net.Data macro variable representing its name. If there is no REPORT block, CLOBs have the .txt extension added to them. These are the recognized LOB formats:

• bitmap (.bmp)

• graphical image format (.gif)

• tag image file format (.tif)

• Postscript (.ps) These must be stored as BLOBs, not CLOBs.

Other file types are not recognized and are not supported. UPDATE and INSERT SQL statements are not supported for any large objects. The first example below displays a picture inline. In the second example, the application user must click on the file name to invoke the viewer.

<IMG SRC="/tmplobs/filename">
<A HREF="/tmplobs/filename">filename</A>

Here is an example of using .WAV files in an application. This file type is not recognized by Net.Data, so a EXEC variable is used to append the extension to the file.

%DEFINE{
docroot="/usr/lpp/internet/server_root/html"
rename=%EXEC "rename $(docroot)$(V3) $(docroot)$(V3).wav"
%}
 
%FUNCTION(DTW_SQL) queryData() {
SELECT Name, IDPhoto, Voice FROM RepProfile
%REPORT{
<P>Here are the images you selected:<P>
%ROW{
$(rename)
$(V1) Voice sample <IMG SRC="$(V2)">
<A HREF="$(V3.wav")>Voice sample</A><P>
%}
%}
%}
 
%HTML(REPORT){
@queryData()
%}

The queryData function returns the following HTML:

<P>Here are the images you selected:<P>
Kinson Yamamoto
<IMG SRC="/tmplobs/p2345n1.gif">
<A HREF="/tmplobs/p2345n2.wav">Voice sample</A><P>
Merilee Lau
<IMG SRC="/tmplobs/p2345n3.gif">
<A HREF="/tmplobs/p2345n4.wav">Voice sample</A><P>

This REPORT block uses the implicit table variables V1, V2, and V3.

• V1 is a person's name, which is plain text.

• V2 is a photo of the person in a .GIF file. The image is shown inline. Net.Data includes the temporary LOB directory and .GIF extension automatically.

• V3 is a sample of the person's voice in a .WAV file. When Net.Data encounters an unrecognized file format, such as a .WAV file, it writes the file into the temporary LOB directory without a file extension. This example shows how to handle this file type by adding the extension using an EXEC variable. When the variable $(V3) is resolved, it has the path /tmplobs/ added before the file name. For example, /tmplobs/sound2a. One way to deal with such files is to write a REXX program to change the slashes to backslashes and rename the files. The voice sample is played when the application user clicks on Voice sample.

Not all Web browsers support graphics and sound. Special hardware and software, such as a sound card and driver, might be required to support the features described here.