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Oracle Tips by Burleson |
Session State
To the seasoned developer, session state can best
be defined in terms of global variables. Session state is the storing
of page item values in the database. Their values can be referenced
from any page in an application. Since they are stored in a database
table and are specific to each HTML DB session, their values can be
referenced in stored procedures.
A big benefit any experienced web developer will
notice immediately is that session state is managed by HTML DB.
Nothing special like saving them in hidden page values has to be
done. Just being able to reference session state from a stored
procedure will show how valuable it is to have HTML DB provide this
ability.
Session state for page items are tied to a page so
all the page items can be set to NULL values by clearing the cachefor a page. It is also possible to set all the page items
in the entire application to NULL by clearing the cache for the
application.
Viewing the values in session state can be done by
using the Session link on the developer toolbar. It is also possible
to view session state for the whole workspace by logging in as an
administrator and navigating to HTML DB Workspace Administration
à Manage Services
à Session State
Navigating to the HTML DB Workspace Administration
is accomplished by clicking on the Administration tab.
Reference Types for
Page Items
While using HTML DB, it will be necessary to
reference the session state for page items. There are several ways,
or reference types, for referring to the page item depending on the
type of code the HTML DB engine is executing. For the most part, page
items in SQL are referenced using the Bind Variable syntax and when
editing page items, their values are set using the Substitution String
syntax.
Bind Variable: Syntax
:P100_CUSTOMER_ID
This syntax is used within the SQL statements for
page processes, page computations, and page validations.
Substitution String:
Syntax &P100_CUSTOMERID.
When a page is rendered, the HTML DB engine will
substitute the text of the substitution string &P100_CUSTOMER_ID. with
the value of the session state, such as the value 231. The syntax of
the substitution string includes a leading ampersand (&) and a
trailing period (.). The substitution strings can be used in region
titles, page items, URL’s, and other locations.
PL/SQL: Syntax V(
'P100_CUSTOMER' )
This is used to reference the session state of
page items from a PL/SQL stored procedure. When the page is
submitted, the session state is stored in HTML DB tables for each of
the page items. The session state can then be referenced by using the
V and NV functions. The V function is for alphanumeric values and the
NV function will return the value as a number.
Template Substitution:
Syntax #P100_CUSTOMER_ID#
This syntax is primarily used in templates to
reference attributes set on attributes pages such as application
attributes, page definition, etc. This syntax is also used on reports
to reference the values returned for columns in an SQL select
statement. One example is to use this syntax in a report column link
to refer to the column in the SQL statement.
Preferences
Preferences comprise a persistent session state
that is maintained between user sessions. That is, when a user logs
out and logs back in, the Preferences can be re-read and used. They
are like variables that last forever between uses of the application.
In HTML DB, the developer may have chosen to
modify the default view from Icons to Details, so HTML DB saved that
selection as a user preference. HTML DB then uses the stored user
preference to know how to display the screen the next time the
developer logs in to do development.
Preferences are user specific. If public
authentication, Page Is Public, is being used for web pages, all users
are authenticated with the same user preferences. Since public pages
do not require a valid user login id, HTML DB uses the username of
NOBODY; therefore, since everyone using public pages is known to HTML
DB as nobody, the preferences are shared among all web users. If the
previous visitor to the web page sorted the report by the Payment Type
column, the next user to visit would see the same sorting due to the
preference being reused. In this case, the developer may want to
create a page process that will reset the preferences as the page is
being rendered. That can be done by creating a Session State page
process with the type set to Reset Preferences (remove all preferences
for current user). This can be handy on report pages where data can
be sorted. In the description above, the preferences are being reset
before loading a report page to restore the default sorting of how the
report was designed. The section in this book on HTML DB APIs
provides more information on the htmldb_util.remove_sort_preferencesprocedure.
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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