Tag: tips-&-tricks

Apex Developer Toolbar Options

One of the things that used to bug me about the Apex developer toolbar was that it sometimes obscured the content I was trying to test at the bottom of the page; you could turn it off but then next thing you want to access it you have to jump through the hoops to turn it back on again.

I just noticed it now has some new display options which solves this problem perfectly:

devtoolbaroptions1

  • Auto Hide – I turn this on so that it slides almost completely out of the way when I don’t want it (move your mouse over it to make it pop out again, click into your page to hide it)
  • Show Icons Only – once you’re familiar with the options you can shrink the toolbar to show only the icons (hover over the icon to see the label)
  • Display Position – put it on the Right-hand side of the window instead of the bottom

A random string of digits

715175039885776956103287888080

I needed to generate a random string with an exact length consisting of numeric digits, that I could send in an SMS to a user as a temporary account “pin”. DBMS_RANDOM.string is unsuitable for this purpose as its supported modes all include alphabetic characters. So I used DBMS_RANDOM.value instead. I call TRUNC afterwards to lop off the decimal portion.

FUNCTION random_pin (digits IN NUMBER)
  RETURN NUMBER IS
BEGIN
  IF digits IS NULL OR digits < 1 OR digits > 39 THEN
    RAISE_APPLICATION_ERROR(-20000,'digits must be 1..39');
  END IF;

  IF digits = 1 THEN
    RETURN TRUNC( DBMS_RANDOM.value(0,10) );
  ELSE
    RETURN TRUNC( DBMS_RANDOM.value(
                    POWER(10, digits-1)
                   ,POWER(10, digits) ));
  END IF;
END random_pin;

random_pin(digits => 6);

482372

EDIT 8/1/2016: added special case for 1 digit

ADDENDUM

Because the requirements of my “pin” function was to return a value that would remain unchanged when represented as an integer, it cannot return a string of digits starting with any zeros, which is why the lowerbound for the random function is POWER(10,digits-1). This, unfortunately, makes it somewhat less than perfectly random because zeroes are less frequent – if you call this function 1000 times for a given length of digits, then counted the frequency of each digit from 0..9, you will notice that 0 has a small but significantly lower frequency than the digits 1 to 9.

To fix this, the following function returns a random string of digits, with equal chance of returning a string starting with one or more zeroes:

FUNCTION random_digits (digits IN NUMBER)
  RETURN VARCHAR2 IS
BEGIN
  IF digits IS NULL OR digits < 1 OR digits > 39 THEN
    RAISE_APPLICATION_ERROR(-20000,'digits must be 1..39');
  END IF;
 
  RETURN LPAD( TRUNC(
    DBMS_RANDOM.value(0, POWER(10, digits))
    ), digits, '0');
END random_digits;

The above functions may be tested and downloaded from Oracle Live SQL.

Detect Empty List

You have a Select List item on your page driven from a dynamic query, e.g. one that only shows valid values. One day, users notice that the list appears empty and raise a defect note.

emptylist.PNG

You check the query behind the list and verify that indeed, the list should be empty because there are no valid values to show. It’s an optional item so the user is free to save the record if they wish.

There are a number of ways we could make this more user-friendly: depending on the specifics of the situation, we might just hide the item, or we might want to show an alternative item or a warning message. We can do any of these things quite easily using either a computation on page load (if the list doesn’t change while the page is open) or a dynamic action.

In the case of my client, they wanted the item to remain on screen, but to show an orange warning message to let them know that there are no gateways currently available; this is only a warning because there are subsequent processes that can handle the missing gateway (e.g. a higher-privileged user can assign a “hidden” gateway to the record if they deem it suitable).

To do this we create a display item (e.g. “P1_NO_GATEWAY_WARNING” which shows the warning message) and a dynamic action with the following attributes:

  • Event = Page Load
  • Condition = JavaScript expression
  • Value = listIsEmpty("P1_GATEWAY_ID")
  • True Action = Set Value
  • Set Type = Static Assignment
  • Value = Warning: no gateways currently available
  • Selection Type = Item(s)
  • Item(s) = P1_NO_GATEWAY_WARNING

In the page’s Function and Global Variable Declaration, or (even better) in the application’s global javascript file, we add the following:

function listIsEmpty(itemName) {
  return $("#" + itemName + " option:enabled").filter(
    function(){return this.text;}
    ).length==0;
}

This was adapted from some solutions here. It looks for all <option>s under the item, filters the list for options which are not disabled and have a label, and returns true if the remaining set is empty. I added the this.text bit because the empty lists generated by Apex include a single empty option for the “NULL” value. This is because I have set the list item’s Null Display Value to blank (null).

emptylistwarning

Tabular Form – set default values with jQuery

tabular-form-default-jquery4

I have a simple tabular form with a numeric “sort order” column. I want the value of this column to be defaulted automatically, based on the maximum value of the rest of the records on the screen. Unfortunately the builtin Apex default type for columns in a tabular form can only be based on an Item, or a PL/SQL expression or function. I didn’t want to make a database call to get the maximum value because the user may have added multiple records which have not yet been saved to the database.

I tried basing the default on a hidden page item which I kept updated based on the values entered, but it seems the tabular form only gets the item’s value on page load and doesn’t re-examine the item’s value when you click the “Add” button. Instead, I had to turn to javascript and jQuery to get the job done.

1. Add a class to the tabular form column by setting the Element CSS Classes column attribute (I’ve used “sortorder” as the class name).

tabular-form-default-jquery2

2. Add a javascript function to the page that searches for all the “sortorder” items, calculates the maximum value and adds 10, and assigns it to the last sortorder item on the page.

function setNextSortOrder() {
  var highest=0;
  $(".sortorder").each(function(){
    if (this.value != "") {
      highest=Math.max(highest,parseFloat(this.value));
    }
  });
  $(".sortorder").last().val(highest+10);
}

tabular-form-default-jquery1

3. Modify the javascript for the “Add” button to call the setNextSortOrder function immediately after adding a row.

javascript:{apex.widget.tabular.addRow();setNextSortOrder();}

tabular-form-default-jquery3

It’s a bit hackish and might not work correctly in some cases but it’ll do for now.

Apex CSV Import: “Data Loading Failed”

If you are using the Apex built-in Data Loading feature to allow your users to upload CSV files, you may have encountered this error.

Data-Loading-Failed
(Note: the error may appear differently in your application as I have built a custom error handling function)

It’s not a particularly useful message, and the logs don’t seem to shed much light on the problem either – reporting only the following:

DATA_LOAD - Final collection is created
...Execute Statement: select 1 from "DEMO"."MY_TABLE" where "RECORD_ID" = :uk_1
Add error onto error stack
...Error data:
......message: Data Loading Failed
......additional_info: ORA-01403: no data found
...
......ora_sqlerrm: ORA-01403: no data found
......error_backtrace:
  ORA-06512: at "APEX_040200.WWV_FLOW_DATA_UPLOAD", line 4115
  ORA-06512: at "APEX_040200.WWV_FLOW_PROCESS_NATIVE", line 213
  ORA-06512: at "APEX_040200.WWV_FLOW_PROCESS_NATIVE", line 262
  ORA-06512: at "APEX_040200.WWV_FLOW_PLUGIN", line 1808
  ORA-06512: at "APEX_040200.WWV_FLOW_PROCESS", line 453

After trial and error I tracked down one potential cause of this error so I thought I’d share it in case it happens again. I’ll probably come across this again later and forget what the solution was and find this article.

In my case (Apex 4.2.4), the problem was caused by an invalid entry in the Column Name Aliases list of values. I was using a custom List of Values so that alternative names for the columns would be automatically mapped without the user having to select them every time. To do this, I had to edit the List of Values directly to add the alternative names; but I had mistyped one of the Return Values which must map to a real column name on the target table. Whenever I picked this column for an import, I’d get the “Data Loading Failed” error message. Correcting the return value resolved the issue.

In order to stop this happening again, I added the following check to my Apex QA script (this is run whenever the application is deployed):

PROMPT Invalid dataload column mappings (expected: none)
SELECT REPLACE(lt.owner,'#OWNER#',USER) AS owner
      ,lt.table_name
      ,le.return_value  AS target_column_not_found
      ,le.list_of_values_name
      ,le.display_value AS col_alias
      ,lt.application_id
      ,lt.application_name
      ,lt.name AS dataload_definition
FROM   apex_appl_load_tables lt
JOIN   apex_application_lov_entries le
ON     le.lov_id = lt.column_names_lov_id
WHERE NOT EXISTS (
  SELECT NULL
  FROM   all_tab_columns tc
  WHERE  tc.owner = REPLACE(lt.owner,'#OWNER#',USER)
  AND    tc.table_name = lt.table_name
  AND    tc.column_name = le.return_value)
ORDER BY lt.name, le.display_sequence;

If the above query returns any rows, it’ll be a problem.