In his 3 part series ending with APEX and the Order Items are Submitted, Martin D’Souza did a great job explaining how APEX page items are submitted and why you can’t reorder the DOM in arbitrary ways. If you haven’t read it already it I strongly recommend that you do so. I can’t improve on how he explained it but I have just two things to add.
Why does APEX do this?
I was very confused by this when I first joined the APEX team. I think that others especially people with front end web development experience will also wonder why APEX uses p_arg_names and p_tnn names rather than the more traditional way where you get to name your inputs as you please. For example <input name="phone_number"...>.
Martin explains that the p_arg_names values are used to map the post parameter values back to the APEX item metadata. The other part of the puzzle has to do with how HTTP post parameters are passed into the APEX engine. The interface between the web listener and APEX Engine maps post parameters to PL/SQL procedure formal parameter names. So there is actually a PL/SQL procedure with formal parameters named p_arg_names and p_t01, p_t02…p_t200. The same procedure is used for all apps and all pages so this is why fixed names must be used.
A subtle and unfortunate consequence.
If you have used any APEX applications you have undoubtedly run into the situation shown in the following image where the browser auto complete feature offers suggestions that have nothing to do with the current field.
How a browser implements the auto complete feature is up to the browser (meaning there is no common specification that must be followed) but the primary method of choosing what values to show is the name attribute. Fields with the same name tend to show the same auto complete choices. The underlying assumption that browsers are making is that web developers choose meaningful names for input fields such as firstName, phone_number, etc. With APEX this assumption fails. Because the name attribute is assigned automatically and sequentially, it is the order of the form item on the page that determines what auto complete values will be shown.
I’m a little surprised that more people haven’t complained about this. Its a tricky problem to solve and it may not even be worth solving. How bothersome do you find this?
When a page is submitted, APEX engine can derive order of item_ids that should ideally come in p_arg_names array based on item display order and conditions of items/regions. In this case, APEX can throw error, instead of processing page submit? or this can’t be done?
Thanks for the enhancement, like these kind of explanations. Never had the Autocomplete problem in 10 years so far, but good to know that I can explain it know and intimdate my colleagues with this knowledge 🙂