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Oracle Tips by Burleson |
Before Header Computations
Before Header computations are the first pieces of
logic to be executed by the HTML DB engine. A Before Header
computation can set the values of any page item regardless of its
position on the page or which region it is in. It can also reference
a page item set by another before header computation that has a lower
execution sequence.
As shown in Figure 12.6, the P2300_AFTER_HEADER
computation would be able to use the value set in P2300_REGION_1, but
P2300_REGION_1 would not be able to reference the value set in
P2300_AFTER_HEADER. That is because P2300_AFTER_REGION has a higher
sequence (20) and is executed after the other computation (10).
Before Header Processes
Not only is
this execution point performed first, but it is also executed before
any HTML is rendered. Reviewing the HTML code below shows that a
Before Header process writes HTML code before the HTML engine renders
the <html> tag. See the example below. A common use for the before
header process is to populate page items on the application page.
BeforeHeader
Process Point
<html lang="en-us" xmlns:htmldb="http://htmldb.oracle.com">
<head>
The text BeforeHeader Process Point at the top of
Figure 12.8 was written using this type of process.
The above book excerpt is from:
Easy
HTML-DB Oracle Application Express
Create
Dynamic Web Pages with OAE
ISBN 0-9761573-1-4
Michael Cunningham & Kent
Crotty
http://www.rampant-books.com/book_2005_2_html_db.htm
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