Oracle Database Tips by Donald Burleson

Examining APEX's Automatic Row Fetch

It is important to understand what the Automatic Row Fetch is doing.  This, and the next topic, can be difficult concepts to understand so I will attempt to break them down into manageable pieces.  There are several regions on the edit process page for an Automatic Row Fetch (ARF) process, but the most important region is the Source region as seen in Figure 8.4. 

The ARF dynamically performs SQL SELECT statements to populate the session state for page items.  The ARF is set to a process point of On Load - After Header.

Figure 8.4 can be used to illustrate several attributes:

·         Table Owner:  Select the schema name for the owner of the table.

·         Table Name:  Enter the table name or view.  An ARF can only dynamically build SQL Select statements for a single table or view.

·         Item Containing Primary Key Column Value:  This is the page item for the first primary key column.  This item is used to build the WHERE clause of the dynamic SQL statement.  It is common to set this page item in the URL while navigating to the page.  The ARF then uses the value in session state for the WHERE clause and populates the rest of the page items.

·         Primary Key Column:   This is also used in the building of the WHERE clause.  Looking at Figure 8.4, the ARF would build a WHERE clause something like:

WHERE ID = :P12_ID.

·         Item Containing Second Key Column Value:  This is the page item for the second primary key column.  It is also used in the building of the dynamic WHERE clause and mention above.

·         Second Key Column:  The column name for the second database column making up the primary key for the table.  The ARF can only be used for tables that have two or fewer columns making up the primary key.  If the tables have more than two columns for the primary key, it will be necessary to write custom PL/SQL processes.  The realization that ARF only allows for two column primary keys may influence database design.

·         DML Fetch Mode:  There are two modes from which to choose, and how the session state behaves during page rendering depends on this setting.  The recommended setting for this is Set Memory Cache on Fetch.

·         Set Memory Cache on Fetch:   With this setting, the session state for the page items will be set immediately after the dynamic SQL Select is executed.  If there are other page rendering processes that use the values for page items being populated by this ARF, this is the mode that must be used.

·         Set Memory Cache On Display:  Using this setting will not set session state until the page is rendered.  If the developer needs to hide the session state of page items being populated with this process until the page is completely rendered, this is the setting to use.

The explanation of the Valid Request information is in the Examining Automatic Row Processing (DML) section below.

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