Understanding Conditional Rendering and Processing |
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A condition is a small unit of logic that helps you control the display of regions, items, buttons, and tabs as well as the execution of processes, computations, and validations. For example, when you apply a condition to a button, the rendering engine evaluates the condition during the rendering (or Show Page) process. Whether the condition passes or fails determines if the page control (such as a button) displays.
You specify a condition by selecting a condition type when you create the control or component (for example, the region, item, button, or tab) or by making a selection from the Condition Type attribute. Depending upon the Condition Type you select, enter the appropriate values in the Expressions fields. The condition evaluates to true or false based on the values you enter in the Expression fields.
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Note: Whether you use the Expression fields depends upon the selected condition type. Some condition types do not require values in either field, others require a value only for Expression 1, and other condition types require values in both fields. Although these fields are labeled "Expression 1" and "Expression 2", the values for a given condition type do not necessarily conform to any formal definition of the term expression. They are simply text values appropriate for the selected condition type. |
To view a complete listing of all available conditions for a given component or control click the View icon to the right of the Condition Type list. Shortcuts to common selections appear directly beneath the list. If your condition requires an expression, enter it in the appropriate field.
The following sections offer examples of some commonly used condition types.
Current Page in Expression 1
Current page in Expression 1 evaluates to true if the current page ID is contained within the comma-delimited list of pages in Expression 1. For example:
100
If the current page is 100, then this condition evaluates to true and the condition passes.
Exists
Exists (SQL query returns at least one row) is expressed as a SQL query. If the query returns at least one row, then the condition evaluates as true. For example:
SELECT 1 FROM emp WHERE deptno = :P101_DEPTNO
This example references item P101_DEPTNO as a bind variable. You can use bind variables within application processes and SQL query regions to reference item session state. If one or more employees are in the department identified by the value of P101_DEPTNO, then the condition evaluates as true.