Thursday, 5 August 2010

APEX 4.0 Enhancements: Validating Form Data

Oracle Application Express 4.0 introduces lots of big new features; websheets, dynamic actions, plug-ins, RESTful web services, team development, updated charts, the list goes on. But there are also many enhancements to existing functionality that we hope will help to simplify the overall process of developing applications in APEX. One such area, and the focus of this post is how data is validated. This post will give you an overview of what's changed with validations and how these changes will make your daily development life a little easier.


Item-Centric Validation
Historically in APEX if you want to validate data input on a page, you create a validation. The validation is a separate component that you need to define and maintain. Now in APEX 4.0, the actual item can handle some simple validation of the data it receives. For example, all item's (both native to APEX and plug-ins) now have a 'Value Required' attribute. By setting this to 'Yes', APEX will automatically validate a value has been entered and raise an error if not, no separate validation required.

Additional to this 'Value Required' validation, some item types also validate their data, based on how the item is defined. For example, the new 'Number' item type, which you can use for handling numeric data contains settings for 'Minimum Value' and 'Maximum Value'. When these are defined, APEX will automatically validate the data received based on these settings and raise appropriate errors.

Settings for the new 'Number' item, settings highlighting are automatically validated

The new datepicker item in APEX 4.0 also supports this type of automatic validation. Additional to the 'Value Required' setting (available for all items), the datepicker also allows setting 'Format Mask', 'Minimum Date', 'Maximum Date' and 'Year Range'. In doing so, APEX will again automatically validate the data received based on these settings and raise appropriate errors.

Settings for the new 'Date' item, settings highlighting are automatically validated

Plug-in items may also contain automatic validations, depending on whether the plug-in author has coded in this support.

You also have a couple of ways of customising the error message that is displayed by APEX when these validations fail, in terms of content and position. To override the default error messages, please refer to this section of the user guide. This details all of the 'Text Messages' that you would need to define in your applications to override the defaults. If you want to change where the error is displayed on screen, please see the 'Default Error Display Location' attribute available via 'Edit Application Properties' on the application homepage.

Finally, debug mode has also been enhanced to show when these validations are executed and whether they passed or failed.

Item based validations offer a more logical approach to validating data and requires fewer moving parts, which means less to define and less to maintain. Of course, for other more complex situations a separate validation will still be required, but this greatly simplifies some of the more common, simple scenarios.


Button-Centric Validation Exclusion
Again, historically in APEX if you don't want a validation to fire when certain buttons are pressed, you would define that logic in the validation. Let's take an example. If you have a typical 'Form' page used for inserting, updating and deleting data, you may want your validations to fire for insert and update, but not for delete. This would involve going through each validation and setting some condition such as where REQUEST != 'DELETE' or similar, to prevent the validation from firing. Now, in APEX 4.0, the actual button can be defined to either 'Execute Validations' or not.

Specify that pressing the button should not cause any validations to fire.

This is much easier, all you need to do is set this at button level and that's it, no item, plug-in or custom validations will fire. Wizard created forms will set this up for you automatically, so when creating these types of forms, the 'Create' and 'Save' buttons execute validations and the 'Delete' and 'Cancel' buttons do not.

You can also override this at validation level by setting the 'Always Execute' validation attribute to 'Yes' (defaults to 'No'). This could be useful for example if you want to always execute a security check, regardless of any button exclusions.

Debug mode has again been enhanced here to show if validations are prevented from firing because of the button setting.


Tabular Form Validations
APEX 4.0 now also supports declarative validation of tabular form data. Before APEX 4.0, there was no declarative support for validating this type of form and you would have to do a lot of manual PL/SQL to validate your data. Currently, tabular form validations only support a subset of what's available with page item validation, but do cater for some of the more common scenarios (required values, type checks and string comparisons). We are looking to extend this in a future release of APEX.


Error Message Label Placeholders
This is small but one of my favourites. When defining an error message that displays when a validation fails, if the validation is associated with a specific page item, you can now use the #LABEL# placeholder to dynamically reference the associated item's label.

Use #LABEL# instead of hard-coding the associated item label text.

So instead of having to duplicate the label text in the error message (and have to remember to change it if you change the item's label) as was historically the case, just use the #LABEL# placeholder and that's it. Again, less to define and less to maintain. An equivalent placeholder is also available for the new tabular form validations, #COLUMN_HEADER#.


Upgrading Applications
So finally, what about your existing APEX applications that have been long since built, where you want to take advantage of some of these new features. Well, take a look at the 'Upgrade Application' feature available via the 'Utilities' menu from the application homepage. This assists you in upgrading your application to use some of the new features in APEX 4.0.

Of particular relevance to validations are the following upgrade types:
  • Update Text Field Item to Number Field Item, where appropriate - Locates where you have an unconditional 'Is Numeric' validations on 'Text Field' items and upgrades them to use the 'Number' item type with in-built numeric checking. Also removes the now redundant separate validation.
  • Update Value Required item attribute to Yes, where appropriate - Locates where you have unconditional 'Not Null' validations on items and sets those item's 'Value Required' attribute to 'Yes'. Also removes the now redundant separate validation.
  • Numeric, Required and Date Picker Item updates based upon conditional validations - Just locates where you have conditional validations for 'Is Numeric', 'Not Null' or 'Is Valid Date' on 'Text Field' items, for your manual review. So you can determine if the validation can be replaced with some item settings and button exclusions.


So quite a few little enhancements that hopefully add up to easier and more intuitive data validation. Good luck with your new APEX 4.0 style validations and let us know what you think!

Many thanks to Patrick Wolf for reviewing this post and filling in the gaps.

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