Build your Apex application better – do less in Apex

I recently saw this approach used in a complex Apex application built for my current client, and I liked what I saw – so I used a similar one in another project of mine, with good results.

1. Pages load and process faster
2. Less PL/SQL compilation at runtime
3. Code is more maintainable and reusable
4. Database object dependency analysis is much more reliable
5. Apex application export files are smaller – faster to deploy
6. Apex pages can be copied and adapted (e.g. for different interfaces) easier

How did all this happen? Nothing earth-shattering or terribly original. I made the following simple changes – and they only took about a week for a moderately complex 100-page application (that had been built haphazardly over the period of a few years):

1. All PL/SQL Process actions moved to database packages
2. Each page only has a single Before Header Process, which calls a procedure (e.g. CTRL_PKG.p1_load;)
3. Each page only has a single Processing Process, which calls a procedure (e.g. CTRL_PKG.p1_process;)
4. Computations are all removed, they are now done in the database package

The only changes I needed to make to the PL/SQL to make it work in a database package were that bind variable references (e.g. :P1_CUSTOMER_NAME) needed to be changed to use the V() (for strings and dates) or NV() (for numbers) functions; and I had to convert the Conditions on the Processes into the equivalent logic in PL/SQL. Generally, I would retrieve the values of page items into a local variable before using it in a query.

My “p1_load” procedure typically looked something like this:

PROCEDURE p1_load IS
BEGIN
  msg('p1_load');
  member_load;
  msg('p1_load Finished');
END p1_load;

My “p1_process” procedure typically looked something like this:

PROCEDURE p1_process IS
  request VARCHAR2(100) := APEX_APPLICATION.g_request;
BEGIN
  msg('p1_process ' || request);
  CASE request
  WHEN 'CREATE' THEN
    member_insert;
  WHEN 'SUBMIT' THEN
    member_update;
  WHEN 'DELETE' THEN
    member_delete;
    APEX_UTIL.clear_page_cache(APEX_APPLICATION.g_flow_step_id);
  WHEN 'COPY' THEN
    member_update;
    sv('P1_MEMBER_ID'); -- clear the member ID for a new record
  ELSE NULL;
  END CASE;
  msg('p1_process Finished');
END p1_process;

I left Validations and Branches in the application. I will come back to the Validations later – this is made easier in Apex 4.1 which provides an API for error messages.

It wasn’t until I went through this exercise that I realised what a great volume of PL/SQL logic I had in my application – and that PL/SQL was being dynamically compiled every time a page was loaded or processed. Moving it to the database meant that it was compiled once; it meant that I could more easily see duplicated code (and therefore modularise it so that the same routine would now be called from multiple pages). I found a number of places where the Apex application was forced to re-evaluate a condition multiple times (as it had been copied to multiple Processes on the page) – now, all those processes could be put together into one IF .. END IF block.

Once all that code is compiled on the database, I can now make a change to a schema object (e.g. drop a column from a table, or modify a view definition) and see immediately what impact it will have across the application. No more time bombs waiting to go off in the middle of a customer demo. I can also query ALL_DEPENDENCIES to see where an object is being used.

I then wanted to make a Mobile version of a set of seven pages. This was made much easier now – all I had to do was copy the pages, set their interface to Mobile, and then on the database, call the same procedures. Note that when you do a page copy, that Apex automatically updates all references to use the new page ID – e.g. if you copy Page 1 to Page 2, a Process that calls “CTRL_PKG.p1_load;” will be changed to call “CTRL_PKG.p2_load;” in the new page. This required no further work since my p1_load and p1_process procedures merely had a one-line call to another procedure, which used the APEX_APPLICATION.g_flow_step_id global to determine the page number when using page items. For example:

PROCEDURE member_load IS
  p VARCHAR2(10) := 'P' || APEX_APPLICATION.g_flow_step_id;
  member members%ROWTYPE;
BEGIN
  msg('member_load ' || p);  
  member.member_id := nv(p || '_MEMBER_ID');  
  msg('member_id=' || member.member_id);  
  IF member.member_id IS NOT NULL THEN    
    SELECT *
    INTO   member_page_load.member
    FROM   members m
    WHERE  m.member_id = member_load.member.member_id;    
    sv(p || '_GIVEN_NAME',        member.given_name);
    sv(p || '_SURNAME',           member.surname);
    sv(p || '_SEX',               member.sex);
    sv(p || '_ADDRESS_LINE',      member.address_line);
    sv(p || '_STATE',             member.state);
    sv(p || '_SUBURB',            member.suburb);
    sv(p || '_POSTCODE',          member.postcode);
    sv(p || '_HOME_PHONE',        member.home_phone);
    sv(p || '_MOBILE_PHONE',      member.mobile_phone);
    sv(p || '_EMAIL_ADDRESS',     member.email_address);
    sv(p || '_VERSION_ID',        member.version_id);
  END IF; 
  msg('member_load Finished');
END member_load;

Aside: Note here the use of SELECT * INTO [rowtype-variable]. This is IMO the one exception to the “never SELECT *” rule of thumb. The compromise here is that the procedure will query the entire record every time, even if it doesn’t use some of the columns; however, this pattern makes the code leaner and more easily understood; also, I usually need almost all the columns anyway.

In my database package, I included the following helper functions at the top, and used them throughout the package:

DATE_FORMAT CONSTANT VARCHAR2(30) := 'DD-Mon-YYYY';

PROCEDURE msg (i_msg IN VARCHAR2) IS
BEGIN
  APEX_DEBUG_MESSAGE.LOG_MESSAGE
    ($$PLSQL_UNIT || ': ' || i_msg);
END msg;

-- get date value
FUNCTION dv
  (i_name IN VARCHAR2
  ,i_fmt IN VARCHAR2 := DATE_FORMAT
  ) RETURN DATE IS
BEGIN
  RETURN TO_DATE(v(i_name), i_fmt);
END dv;

-- set value
PROCEDURE sv
  (i_name IN VARCHAR2
  ,i_value IN VARCHAR2 := NULL
  ) IS
BEGIN
  APEX_UTIL.set_session_state(i_name, i_value);
END sv;

-- set date
PROCEDURE sd
  (i_name IN VARCHAR2
  ,i_value IN DATE := NULL
  ,i_fmt IN VARCHAR2 := DATE_FORMAT
  ) IS
BEGIN
  APEX_UTIL.set_session_state(i_name, TO_CHAR(i_value, i_fmt));
END sd;

PROCEDURE success (i_msg IN VARCHAR2) IS
BEGIN
  msg('success: ' || i_msg);
  IF apex_application.g_print_success_message IS NOT NULL THEN
    apex_application.g_print_success_message :=
      := apex_application.g_print_success_message || '<br>';
  END IF;
  apex_application.g_print_success_message
    := apex_application.g_print_success_message || i_msg;
END success;

Another change I made was to move most of the logic embedded in report queries into views on the database. This led to more efficiencies as logic used in a few pages here and there could now be consolidated in a single view.

The challenges remaining were record view/edit pages generated by the Apex wizard – these used DML processes to load and insert/update/delete records. In most cases these were on simple pages with no other processing added; so I left them alone for now.

On a particularly complex page, I removed the DML processes and replaced them with my own package procedure which did the query, insert, update and delete. This greatly simplified things because I now had better control over exactly how these operations are done. The only downside to this approach is that I lose the built-in Apex lost update protection mechanism, which detects changes to a record done by multiple concurrent sessions. I had to ensure I built that logic into my package myself – I did this with a simple VERSION_ID column on the table (c.f. Version Compare in “Avoiding Lost Updates”).

The only downsides with this approach I’ve noted so far are:

1. a little extra work when initially creating a page
2. page item references are now strings (e.g. “v('P1_RECORD_ID')“)  instead of bind variables – so a typo here and there can result in somewhat harder-to-find bugs

However, my application is now faster, more efficient, and on the whole easier to debug and maintain – so the benefits seem to outweigh the downsides.