Implementing a reusable APEX form validation definition for multiple, similar page items - oracle

Question

I am currently using APEX 4.0. I would like to make a validation that would apply for multiple fields in a form. For example, I want specific fields to only accept a Y or N, and they must be uppercase letters. As of now, I have one validation for each field. Is there a way to make a single validation that would apply to all these fields?

Answer 1

Creating Re-Usable Form Validations in Oracle Application Express (APEX)
This solution was developed on a Apex instance hosted on Oracle OTN (apex.oracle.com). This instance is currently at version 4.2.5, but the design elements discussed within this solution should still be compatible across the versions from 4.0.0 and 4.2.5.
The way you can approach your form design is not necessarily to catch exceptions through a validation step once the form has been completed and submitted.
Instead, simply consider limiting the choices that the user can choose in their input, and control how that input is interpreted once it is submitted as changes to your data table.
Pre-Validate By Defining Restrictive Value Choices
Here is an example of the OP requirement defined as a "Shared Component" through the "Application Builder" menu. Create a named LOV (list of values) with a static definition. Here, you can define the value pairs of:
DISPLAY, which is anything user friendly you want the user to see. Even if Y or N is pretty self-explanatory, explore other options such as spelling it out (such as: YES) or combining the real value with the display (such as: Y (Yes)).
RETURN VALUE, which is where you enforce what goes into your database. In this case, the uppercase, single character values mentioned in the OP requirements would go here.
This is what that LOV definition looks like:
APEX LOV (list of values) Design Screen
Eliminate Free-form Data Form Item Display Types
Following with the initial concept of a limiting LOV, convert all your form items to use display-types which use a "List of Values" definition pointing to your "Shared Component" (or Named LOV).
Use the SAME LOV definition for questions requiring the same input rules. Now the user has no way of changing the data values outside of the OP definition, and there is some flexibility to use more instructive/descriptive display values so that they are more likely to make the right selection as well.
This is an example of how a input form with the same input data types can accomplish this task with no additional validation:
Sample APEX Form Design with Reusable Input Restriction Rules
In this example, I experimented with a few form item styles, including
The standard text-box entry field. (Problematic without coupling it with additional validation logic).
Select-list entry items worked the best. See the discussion at the end of this solution for more explanation on choosing specifics such as specifying "null field values".
Radio group selection buttons work well to as they provide a visual layout of the valid form choices without additional drilling-down or scrolling.
All three options used the same LOV definition.
Examples of Data Input Using LOV Enforced Restrictions
After experimenting with different kinds of inputs, here's a few things that may be helpful depending on the situation or the deeper requirements of this OP or other readers.
DISPLAY EXTRA VALUES should be left as set to NO. This is the reason for restricting the input possibilities in the first place.
DISPLAY NULL VALUE is best as NO if all answers require a response. If NULL is possible, there is a useful third (defaulted) value that can be used for additional user-friendliness.
Sample Data Inputs and Values from the LOV Restricted Form
Notice that the free-text entry field presents additional problems with data quality without some other form of validation or checking. The other form fields provided accurate data input reflected through the target database table.
Some Closing Comments and Points for Further Study
This solution is only a partial one with respect to protecting information stored in a database table. It is not uncommon for lots of other systems, applications, programs, api's, etc. to also have access to change or add data to this back-end data source.
What if another group of developers independently created an api for managing data in the same table? Unless they read the documentation of the OP or examined existing data sets already present, their project team may not have designed an accurate interpretation of the rules which sit at this point, only on this particular APEX application.
Depending on how vulnerable your system is, it is also good practice to apply relevant safeguards, such as schema level table constraints (such as check constraints), Not Null constraints (where applicable) and even DEFAULT values settings (established by triggers or table default values).
From the Author...
Again, it isn't all necessary to go to this detail... if the input form of the Apex application offers only two choices: "SOUP" or "SALAD", it is unlikely that "BACON-ORANGE-CHICKEN" will pop up in the table after deploying the application into users' hands.
This kind of design approach skips a server round trip worth of I/O because the user already know what is on the menu at the initial page loading event.
Although the OP request is very simple and generic (Y for YES or N for NO), it presents a useful pattern for more complex input screening procedures that can happen even before the data is submitted.
Good Luck, All!
Onward.