This section describes how to create application computations.
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To learn more about execution behavior in the case of a validation error, see "What Happens When a Validation Fails?."
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Application Computations are units of logic that set the value of a single page or application-level item and are run at the same point across multiple pages in an application. Like page-level computation, application computations can be based on static values, item values, PL/SQL, or SQL.
A common use of an application item is to store the value of the last page viewed in the application. By storing the value in an item, you can add a back button and then redirect the user to the page number captured by the computation. This type of computation works well, for example, when you need to enable users to back out of an error page.
The following is an example of a computation that stores the last page visited. In this example, the computation:
Stores the last application page visited to an item named LAST_PAGE
Checks that the value of a CURRENT_PAGE_ITEM
is of type PL/SQL Function Body with a Computation body of:
BEGIN :LAST_PAGE := nvl(:CURRENT_PAGE,:APP_PAGE_ID); :CURRENT_PAGE := :APP_PAGE_ID; RETURN :LAST_PAGE; END;
Typically an application computation runs at the same point across multiple pages in an application. The exception is computations having a Computation Point of On New Instance. These types of computations are useful when you only need to retrieve information once within a user's session. For example, if the application items do not depend on the logged in user, you can initialize them using the Computation Point On New Instance. To look up information that depends on the user, you can also use After Authentication.
If you configure applications to share the same session by setting the same cookie name in the authentication scheme, On New Instance and After Login, the application processes fire whenever Oracle Application Express first processes a request for the application (that is, On New Instance), or processes a request of an authenticated user for the application (that is, After Authentication).
To create an application computation:
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Once you create an application computation, you can view the Application Computation History report. The Application Computation History report displays a history of recently changed application computations by date.
To access the Application Computation History report:
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