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  Oracle Database Tips by Donald Burleson

Examining APEX's Automatic Row Processing (DML)

It is also important to understand what the Automatic Row Processing is doing for us.  Navigate to the Process Row of CONFERENCE_RSVP page process by clicking on the link in the Processes section under Page Processing.  Not to diminish the importance of the other regions, the most important region in the Automatic Row Processing (DML) process in the Source region as shown in Figure 8.5.  For the rest of the discussion, Automatic Row Processing will be referred to as ARP.

The ARP dynamically performs SQL INSERTs, UPDATEs, and DELETEs.  Page items can either be set to participate in the dynamic SQL statements or not.  Adding a page item to participate in the dynamic SQL statements is explained later in the section, Adding a Page Item to a Form.  The ARP is set to a process point of On Submit - After Computations and Validations.  That way validation for all page items can be performed before attempting to update the data in the database.

         Allowed Operations:  The values here indicate the types of dynamic SQL that can be utilized by this ARP.  For example, if the developer does not want to allow any DELETE operations, the Delete option would be unchecked.  Many database systems today do not do DELETEs; they simply mark the row as an inactive row.  In that case, a custom page process would be created to update the database record.

         Return Key Into Item:  During an INSERT process, there may be triggers that populate the primary key columns during INSERT.  The value returned will be based on the column identified in the Primary Key Column above and will be returned into a page item entered here.  In the example in Figure 8.5, the value inserted in the id column would be returned and the session state would be set for the item entered in the Return Key Into Item field.  The value returned could then be used by subsequent page processes.

         Valid Update Request Values:  These are REQUEST values that will cause the ARP to generate and execute the dynamic UPDATE statement.  Developers need to know this if they create their own buttons on a page.  The REQUEST for the button must be set to one of these values if the developer wants the button to cause the ARP to perform an UPDATE.

         Valid Insert Request Values:  These are REQUEST values that will cause the ARP to generate and execute the dynamic INSERT statement.  Set the REQUEST for any user created buttons to one of these values to cause the button to drive the ARP to perform an INSERT.

         Valid Delete Request Values:  These are REQUEST values that will cause the ARP to generate and execute the dynamic DELETE statement.  Set the REQUEST for any user created buttons to one of these values to cause the button to drive the ARP to perform an DELETE.

Special Note About REQUEST and Database Action

The previous section mentioned the Valid Request Values.  The Database Action was also mentioned earlier.  Either one of these can cause the Automatic Row Processing (DML) to produce dynamic SQL.

            Example 1:  If we were to change the name of the SAVE button to SAVESOMETHING, the ARP would still perform an UPDATE because the Database Action is set to SQL UPDATE action.  At that point, the Database Action takes precedence over the name of the button.  In fact, the SQL UPDATE action sets the REQUEST to SAVE.

            Example 2:  If we kept the button name as SAVE and removed the Database Action, the ARP would again work because the REQUEST is set to a value matching the name of the button.  In this case, the REQUEST would be SAVE.  Since SAVE is one of the Valid Update Request Values, the ARP will still produce a dynamic UPDATE statement.

It is apparent that there is more than one way to cause the ARP to produce dynamic SQL.


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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