Export CLOB as a SQL Script #JoelKallmanDay

Quite often I will need to export some data from one system, such as system setup metadata, preferences, etc. that need to be included in a repository and imported when the application is installed elsewhere.

I might export the data in JSON or CSV or some other text format as a CLOB (character large object) variable. I then need to wrap this in suitable commands so that it will execute as a SQL script when installed in the target system. To do this I use a simple script that takes advantage of the APEX_STRING API to split the CLOB into chunks and generate a SQL script that will re-assemble those chunks back into a CLOB on the target database, then call a procedure that will process the data (e.g. it might parse the JSON and insert metadata into the target tables).

This will work even if the incoming CLOB has lines that exceed 32K in length, e.g. a JSON document that includes embedded image data encoded in base 64, or documents with multibyte characters.

This is clob_to_sql_script:

function clob_to_sql_script (
    p_clob           in varchar2,
    p_procedure_name in varchar2,
    p_chunk_size     in integer := 8191
) return clob is

-- Takes a CLOB, returns a SQL script that will call the given procedure
-- with that clob as its parameter.

    l_strings apex_t_varchar2;
    l_chunk   varchar2(32767);
    l_offset  integer;        

begin

    apex_string.push(
        l_strings,
        q'[
declare
l_strings apex_t_varchar2;
procedure p (p_string in varchar2) is
begin
    apex_string.push(l_strings, p_string);
end p;
begin
]');
    
    while apex_string.next_chunk (
        p_str    => p_clob,
        p_chunk  => l_chunk,
        p_offset => l_offset,
        p_amount => p_chunk_size )
    loop
        apex_string.push(
            l_strings,
            q'[p(q'~]'
            || l_chunk
            || q'[~');]');
    end loop;    

    apex_string.push(
        l_strings,
        replace(q'[
    #PROC#(apex_string.join_clob(l_strings));
end;
]',
            '#PROC#', p_procedure_name)
        || '/');

    return apex_string.join_clob(l_strings);
end clob_to_sql_script;

Note that the default chunk size is 8,191 characters which is the safe limit for multi-byte characters. You can choose a smaller chunk size if you want, although if the incoming CLOB is very large, the smaller the chunk size the bigger the expanded SQL script will be.

A simple test case will demonstrate what it will do:

declare
    l_input  clob;
    l_output clob;
begin
    l_input := q'[
{
    "data": "Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum."
}
]';
    l_output := clob_to_sql_script(
        p_clob           => l_input,
        p_procedure_name => 'mypackage.import',
        p_chunk_size     => 60 );
    dbms_output.put_line( l_output );
end;
/

The above script would output this:

declare
l_strings apex_t_varchar2;
procedure p (p_string in varchar2) is
begin
    apex_string.push(l_strings, p_string);
end p;
begin

p(q'~
{
    "data": "Lorem ipsum dolor sit amet, consectetur adip~');
p(q'~iscing elit, sed do eiusmod tempor incididunt ut labore et d~');
p(q'~olore magna aliqua. Ut enim ad minim veniam, quis nostrud ex~');
p(q'~ercitation ullamco laboris nisi ut aliquip ex ea commodo con~');
p(q'~sequat. Duis aute irure dolor in reprehenderit in voluptate ~');
p(q'~velit esse cillum dolore eu fugiat nulla pariatur. Excepteur~');
p(q'~ sint occaecat cupidatat non proident, sunt in culpa qui off~');
p(q'~icia deserunt mollit anim id est laborum."
}
~');

    mypackage.import(apex_string.join_clob(l_strings));
end;
/

The source can be downloaded from here: clob_to_sql_script.sql


Protect your APEX app from URL Tampering – in just a few clicks

Recently I’ve been reviewing and updating my knowledge of APEX security, especially protection from URL tampering. I’ve read the documentation, a number of blogs, and heard from people with experience in the field such as Lino. By default, when you create a new application in APEX you get the following security settings set automatically, which is a good start:

  • Application Session State Protection is Enabled.
  • Each page has Page Access Protection set to Arguments Must Have Checksum.
  • Each Application Item has Protection Level set to Restricted – May not be set from browser.
  • Each Primary Key Item* created by a wizard has Protection Level set to Checksum Required – Session Level.

(* that is, any item mapped from a table column that is, or forms part of, a Primary Key constraint).

These default settings are considered best practice. If you change these, it becomes your responsibility to ensure that your application is protected against security vulnerabilities from URL tampering.

For page items, however, the Protection Level defaults to Unrestricted. This is ok for Form items because the page fetch process will set their values on page load, rendering any attempt at URL tampering ineffective.

For non-form page items, unless the Page Access Protection is relaxed (Unrestricted), leaving items unrestricted is safe since URL tampering is blocked for the entire page anyway. At runtime, if a malicious visitor tries to modify the item value via the URL, they will get the error “No checksum was provided to show processing for a page that requires a checksum when one or more request, clear cache, or argument values are passed as parameters.

Error message "No checksum was provided to show processing for a page that requires a checksum when one or more request, clear cache, or argument values are passed as parameters."

However, what if a developer later needs to change the page to Unrestricted? They may unwittingly introduce a potential URL tampering issue because one or more items were not protected.

UPDATE: in fact, this applies even if it’s a different page in the same application. As Martin D’Souza pointed out a decade ago, URL tampering for any item in the application is possible from any page in the application that is Unrestricted.

The majority of these items are editable input items, so the fact that someone may input a value via the URL is not a big deal. However, for Hidden and Display Only items, it is common for application logic to depend on their values; this logic may be adversely affected by malicious values supplied via the URL.

In some cases, this default is needed in order for the application to work. Some examples when an item must be left Unrestricted are:

  • An item is changed by a Dynamic Action (whether via a Set Item Value, via the Items to Return of a Execute Server-side Code action, or in some custom JavaScript), and cannot have Value Protected set because the page may be submitted.
  • We do actually intend the item to be set via the URL, e.g. when an external web page has a link that sets the item’s value.

In all these cases, the application must be designed to ensure it does not “trust” the value of these items; it should apply suitable checks to ensure the values are valid.

In most cases, it is best practice to set the item Protection Level to Checksum Required – Session Level (or Restricted – May not be set from browser where supported).

You can use a query like this to discover all items that may need to be reviewed:

select
    i.application_id,
    i.page_id,
    i.page_name,
    i.region,
    i.item_name,
    i.display_as
from apex_application_page_items i
where i.application_id = :app_id
and i.item_protection_level = 'Unrestricted'
and i.display_as_code in ('NATIVE_HIDDEN','NATIVE_DISPLAY_ONLY')
order by i.application_id, i.page_id, i.region, i.item_name;
Report showing APPLICATION_ID, PAGE_ID, PAGE_NAME, REGION, ITEM_NAME, DISPLAY_AS, listing two Display Only items (P1_DISPLAY_ONLY_ITEM, P1_DISPLAY_ONLY_ITEM_DA) and two Hiden items (P1_HIDDEN_ITEM, P1_HIDDEN_ITEM_DA) that have Item Protection Level set to "Unrestricted".

Other excellent options are using third-party security scanners such as APEXSec and APEX-SERT to alert you to potential issues in your application. We mandate the use of tools like these internally at Oracle for our own applications and they are a great help.

Using the Session State Protection Wizard

One easy step you can take right now is to use the Session State Protection wizard. It gives you a quick overview of what level of protection your application has against URL tampering, and gives an easy way of fixing the relevant attributes in bulk.

You can access the wizard via Shared Components > Session State Protection

Screenshot of part of App Builder Shared Components; under the Security heading, we want to click on "Session State Protection".

Alternatively, you can access the wizard via Edit Application Definition > Security > Session State Protection > Manage Session State Protection

Screenshot of part of the App Builder Edit Security Attributes page, under the Security tab. In the Session State Protection section, we want to click on the button "Manage Session State Protection".

The wizard starts by showing an overview of the current state of your application’s protection against URL tampering.

Screenshot of the App Builder Session State Protection overview page.
It indicates that my application has Session State Protection = Enabled.
It shows that one page is set to "Arguments Must Have Checksum", one page allows "No URL Access", and one page is "Unrestricted".
It indicates that all 9 Page Items in the application are set to "Unrestricted".
It indicates that of the application's Application Items, one is set to "Restricted - May not be set from browser", one is "Checksum Required - Session Level", and one is "Unrestricted".
Next to each category a ">" icon button is shown.
At the bottom of the page is the button "Set Protection".

You can see if your application has Session State Protection enabled (which it should, really), and if any pages, page items, and/or application items are unprotected. In my sample app here, it’s obvious that there are some potential security issues that need to be reviewed.

You can click the > buttons next to each category to list all the pages and items that need to be reviewed.

The main things to watch out for are Pages, Page Items, and Application Items that are set to Unrestricted. Other values are generally fine.

If you see any Items which are set to Checksum Required but not at the Session Level, you may find that a developer has simply set them incorrectly and you should consider changing them to Session Level. However, there are some scenarios where the other levels (Application Level, or User Level) are required.

Now, I might now go through the application page-by-page and set the protection level on each page and item as appropriate. This could be a laborious process for a large application.

A good alternative is to use this wizard to set the protection level in bulk. In this case, I’m going to click Set Protection.

Screenshot of page 1 of the Session State Protection Wizard.
It is asking to Select an Action - either "Disable", or "Configure". I have selected "Configure".
Buttons at the bottom of the page allow me to Cancel, or go to the Next page.
I’ve selected the action Configure, then click Next.
Screenshot of page 2 of the Session State Protection Wizard.
This page allows me to select the Page Access Protection (defaulted to "Arguments Must Have Checksum"), the Page Data Entry Item Protection, the Page Display-Only Item Protection, and the Application Item Protection. These last three are all defaulted to "Checksum Required - Session Level".
Buttons at the bottom of the page allow me to go to the Previous page, Cancel, or go to the Next page.
The wizard now gives me the opportunity to modify the protection level on my pages and items in bulk. I’m going to accept the defaults (Arguments Must Have Checksum / Checksum Required – Session Level) because they are appropriate for most cases in my application.
Screenshot of the last page of the Session State Protection Wizard.
This allows me to confirm the changes that will be made to pages and items in the application.
Buttons at the bottom of the page allow me to go to the Previous page, Cancel, or Finish.
After reviewing the summaries of the changes that the wizard will make, I click Finish.
Screenshot of the App Builder Session State Protection overview page, after running the wizard.
The page now indicates that all 3 pages in my application are set to "Arguments Must Have Checksum", that all 9 Page Items and the 3 Application Items are now set to "Checksum Required - Session Level".

Perfect!

Final Steps

Now, I need to check for hidden page items that are now restricted that might need to be returned to Unrestricted. Otherwise, users will see the error “Session state protection violation” when they submit the page, if a dynamic action has changed them.

Screenshot of an error message alert, saying "1 error has occurred: Session state protection violation: This may be caused by manual alteration of protected page item P1_DISPLAY_ONLY_ITEM_DA. If you are unsure what caused this error, please contact the application administrator for assistance."

The following query will alert me to any Hidden items that have Value Protected switched off (e.g. because they need to be submitted):

select
    i.application_id,
    i.page_id,
    i.page_name,
    i.region,
    i.item_name,
    i.display_as
from apex_application_page_items i
where i.application_id = :app_id
and i.item_protection_level != 'Unrestricted'
and i.display_as_code = 'NATIVE_HIDDEN'
and i.attribute_01 = 'N' -- Value Protected
order by i.application_id, i.page_id, i.region, i.item_name;
Report showing APPLICATION_ID, PAGE_ID, PAGE_NAME, REGION, ITEM_NAME, DISPLAY_AS listing one entry for "P1_HIDDEN_ITEM_DA", a hidden item that is set to "Unrestricted" and has attribute_01 (Value Protected) set to "N".

Now I can review this item to check if Value Protected really needed to be switched off. If the page is never submitted, or the item is never changed by any dynamic actions, this could be switched On. Otherwise, I need to set the item protection to Unrestricted in order for the page to work.

Having made changes to the application, I need to test to ensure I haven’t introduced any issues. My focus will be mainly on the following areas:

  1. Navigation – e.g. do the View or Edit buttons in all reports still work?
  2. Dynamic actions – e.g. do all the dynamic actions and custom javascript still work on all pages that set item values?

For #1, I’m looking for any links that include item values that were not correctly built. If the application generates any links using just string concatenation, it will fail if the target page expects a checksum. The application should build these links using declarative link attributes if possible, or by calling apex_page.get_url (or apex_util.prepare_url at least).

For #2, I would test to ensure that after triggering a dynamic action or javascript code that modifies an item’s value, that the form is still submitted (saved) without error.

Further Reading

Thanks to Christian Neumueller for his review and comments on this article.


Oracle’s Numbers

You are probably familiar with some of the data types supported by the Oracle Database for storing numeric values, but you might not be aware of the full range of types that it provides.

Some types (such as NUMBER, INTEGER) are provided for general use in SQL and PL/SQL, whereas others are only supported in PL/SQL (such as BINARY_INTEGER).

There are others (such as DECIMAL, REAL) that are provided to adhere to the SQL standard and for greater interoperability with other databases that expect these types.

Most of the numeric data types are designed for storing decimal numbers without loss of precision; whereas the binary data types (e.g. BINARY_FLOAT, BINARY_DOUBLE) are provided to conform to the IEEE754 standard for binary floating-point arithmetic. These binary types cannot store all decimal numbers exactly, but they do support some special values like “infinity” and “NaN”.

In PL/SQL you can define your own subtypes that further constrain the values that may be assigned to them, e.g. by specifying the minimum and maximum range of values, and/or by specifying that variables must be Not Null.

What do I prefer?

In my data models, I will usually use NUMBER to store numeric values, e.g. for quantities and measurements; for counts and IDs (e.g. for surrogate keys) I would use INTEGER (with the exception of IDs generated using sys_guid, these must use NUMBER).

In PL/SQL, if I need an index for an array, I will use BINARY_INTEGER (although if I’m maintaining a codebase that already uses its synonym PLS_INTEGER, I would use that for consistency). In other cases I will use INTEGER or NUMBER depending on whether I need to store integers or non-integers.

I don’t remember any occasion where I’ve needed to use FLOAT, or the binary types; and of the subtypes of BINARY_INTEGER, I’ve only used SIGNTYPE maybe once or twice. Of course, there’s nothing wrong with these types, it’s just that I haven’t encountered the need for them (yet).

What about Performance?

There are some differences in performance between these data types, but most of the time this difference will not be significant compared to other work your code is doing – see, for example, Connor on Choosing the Best Data Type. Choosing a data type that doesn’t use more storage than is required for your purpose can make a difference when the volume of data is large and when large sets of record are being processed and transmitted.

Reference Chart: Numeric Data Types

This diagram shows all the numeric data types supplied by Oracle SQL and PL/SQL, and how they relate to each other:

This work is licensed under a Creative Commons Attribution 4.0 International License.
PDF version

Storing BIG Integers

From smallest to largest – the maximum finite integer that can be stored by these data types is listed here. It’s interesting to see that BINARY_FLOAT can store bigger integers than INTEGER, but NUMBER can beat both of them:

BINARY_INTEGER2.147483647 x 109
INTEGER9.9999999999999999999999999999999999999 x 1037
BINARY_FLOAT3.40282347 x 1038
NUMBER9.999999999999999999999999999999999999999 x 10125
BINARY_DOUBLE1.7976931348623157 x 10308

To put that into perspective:

Storing SMALL Numbers

The smallest non-zero numeric value (excluding subnormal numbers) that can be stored by these data types is listed here.

BINARY_FLOAT1.17549435 x 10-38
NUMBER1.0 x 10-130
BINARY_DOUBLE2.2250738585072014 x 10-308

These are VERY small quantities. For example:

  • The size of a Quark, the smallest known particle, is less than 10-19 metres and can easily be represented by any of these types.
  • You can store numbers as small as the Planck Length (1.616 × 10-35 metres) in a BINARY_FLOAT.
  • But to store a number like the Planck Time (5.4 × 10-44 seconds), you need a NUMBER – unless you change the units to nanoseconds, in which case it can also be stored in a BINARY_FLOAT.
  • I’m not aware of any specifically named numbers so small that they require a BINARY_DOUBLE; however, there are certainly use cases (e.g. scientific measurements) that need the kind of precision that this type provides.

Further Reading


Reusable Region as a Modal Page

"clone" icon

On a number of pages throughout my application, I needed to build a region containing a fairly complex set of items, along with dynamic actions and other controls to provide a friendly editing experience for the user. This non-trivial set of items with their accompanying dynamic actions and conditions would be needed on several different pages, and in some cases, multiple times on the same page.

Copying all this all over the place would have created a maintenance headache, so I would much prefer to build them only once, and then re-use the same component throughout my application. Unfortunately, APEX does not at this stage support the concept of a reusable region. An idea might be to allow a region to “subscribe” to another region – although this would be tricky because somehow the item names, dynamic action names, etc. would need to be unique but predictable.

Why not use a plugin?

One approach is to build the whole region as a plugin; this would be ideal as the plugin can then be maintained separately and deployed wherever it’s needed; this would have the benefit that it could be reused in multiple applications.

The downside is that I would not be able to use the declarative features of APEX to define the items and dynamic actions within the region; I would have to code most of that in custom HTML, JavaScript and AJAX calls for database interaction. This would then provide a different maintenance challenge for my successors.

Why not put the region on the Global Page?

Another approach would be to build the region on the Global Page; a condition could be used to show it if it’s needed by the current page.

The downsides to this approach include: (a) you can’t reuse it multiple times on a single page; (b) it may be tricky to integrate it on the pages it needs to return data to (although this could be done with some JavaScript); and (c) you have little control over where on each page the region would be shown.

The Global Region idea might work better if is implemented as an Inline Dialog; with some JavaScript it could be made to pop up wherever it’s needed. I haven’t tried this approach, however.

Use a Modal Page

Instead, the approach I took was to use a modal page. This is a page that will pop up as a layer on top of the calling page, making the calling page visible but non-responsive until the user closes the popup. I can then define all the items needed, along with their conditions and dynamic actions, in the one modal page, and then add buttons throughout my application wherever it was needed.

The calling page needs to pass the current value of one or more items to the modal page; these values are not in the database (yet) because the user may be in the middle of editing them, so their current value on screen may be different to the value stored in the table. This means I can’t have the modal page reading the value from the table, and I can’t just pass the value using the link attributes because these are set in stone when the page is rendered.

In order to open the modal page, then, I need to use a dynamic action.

Note that you can’t build the URL for the modal page in JavaScript, because the client-side code cannot calculate the checksum required by the modal page. Instead, I pre-calculate the URL for the modal page using apex_page.get_url which generates the checksum automatically.

When the user clicks the “Edit” button, it needs to first copy the current value of the item into the session state for the modal page; I do this by making the Edit button Defined by Dynamic Action. On click, it executes two actions: (1) Server-side Code to submit the current value of the text item and set the modal item’s value; then (2) JavaScript Code to redirect to the URL I calculated earlier.

The modal page is then shown, allowing the user to make changes to the value. When they click the “OK” button, the modal page closes and returns the value via Items to Return.

Note that the modal page itself never saves any changes to the database, since on the calling page, the user might decide to cancel.

Back on the calling page, the new value is copied back into the page item via a Dialog Closed dynamic action. This sets the value based on the Dialog Return Item.

I’ve built a “dummy” sample app to demonstrate this technique. You can try it out, and download the sample app definition, from here: https://apex.oracle.com/pls/apex/jk64/r/demo-reusable-modal/home

Details

Here is my main page definition, with two regions. Each region has an item that we want to pass to/from our modal page.

Page designer showing two regions defined, "Region 1" and "Region 2"

Each region needs a unique Static ID.

Page designer showing the Static ID for "Region 1" is set to "region1"
Page designer showing the Static ID for "Region 2" is set to "region2"

Each region has a visible Value item, an Edit button, and a hidden item to precalculate the URL for the modal page.

Page designer showing Region 1 has an item "P1_VALUE1", a button "EDIT1", and a hidden item "P1_EDIT_URL1". Region 2 similarly has an item "P1_VALUE2", a button "EDIT2", and a hidden item "P1_EDIT_URL2".

There are no special attributes on the value item(s); they could be a simple text field, a text area, a readonly item, a combination of various item types, or they could be hidden. Typically they would be based on database column(s) and saved in the record being edited.

The “EDIT URL” hidden items are precalculated using an expression, and set to Always, replacing any existing value in session state.

Page designer showing the PL/SQL Expression as the source for P1_EDIT_URL1.

The other edit URL is similar.

Page designer showing the PL/SQL Expression as the source for P1_EDIT_URL2.

The call to apex_page.get_url is used to pass some static values (that are not changed by the page at runtime) to the modal page. These values may be used by the modal page to customise it for the context it was called from.

apex_page.get_url(
    p_page => 'modal',
    p_items => 'P2_ID,P2_OPTION',
    p_values => :P1_ID || ',' || 'Region 1',
    p_triggering_element => '$(''#region1'')'
)

Note that the value of the item is not passed in the URL.

Note that p_triggering_element is a string, constructed to be a jQuery selector referring to the Static ID that was set on the region, so that the right Dialog Closed event will fire (since we may have multiple Edit buttons on the same page).

Tip: if your modal page doesn’t need them, you can omit the p_items and p_values parameters.

The Edit buttons are set to “Defined by Dynamic Action“.

Page designer showing EDIT1 with a dynamic action "on click edit1".

The Server-side Code simply copies the current value of the item into the modal page’s item. This sets the session state on the server, which is then loaded when the modal is opened.

Page designer showing the Execute Server-side Code action runs the code ":P2_VALUE := :P1_VALUE1;", with Items to Submit set to "P1_VALUE1".

The JavaScript Code redirects to the modal page using the URL we calculated on page load.

Page designer showing the Execute JavaScript Code action.
apex.navigation.redirect("&P1_EDIT_URL1.");

The JavaScript Code for Region 2 is the same except it refers to P1_EDIT_URL2.

On page 2, the modal page, I have contrived an example “calculator” which simply breaks the string value into two “parts”, and allows the user to edit each “part” separately; when they click OK, the concatenated value gets returned to the calling page.

Page designer for page 2 ("modal"). It has two editable items "P2_PART1", "P2_PART2", as well as a "hidden items" region with "P2_VALUE", "P2_ID" and "P2_OPTION". The page also has a button region with "CANCEL" and "OK" buttons.

The two “PART” items are calculated on page load with some PL/SQL:

The page has an After Header process "init" which computes some value for P2_PART1 and P2_PART2 based on the value of P2_VALUE. (The expression itself is not important.)

Note that this code is being executed based on the value of P2_VALUE which was set in session state by the calling page.

Just for the sake of the demo, my “calculator” merely sets the value of the hidden P2_VALUE item based on concatenating the two “parts”:

Dynamic action on change of P2_PART1 and P2_PART1 executes some JavaScript which sets the value of P2_VALUE based on the entered values of P2_PART1 and P2_PART2.

Note: you would define whatever items, dynamic actions or other components that you need.

This modal page never saves any changes to the database; that’s the role of the calling page.

The OK button simply closes the dialog, returning the new value of P2_VALUE to the calling page.

Page designer showing the "on Click OK" dynamic action. It runs the Close Dialog action. The Items to Return is set to P2_VALUE.

Back on the calling page, each region has a dynamic action defined on Dialog Closed.

Page designer on page 1, within Region 1, a dynamic action "on close modal1" on the event Dialog Closed.

The Set Value action copies the Dialog Return Item value into the appropriate item on the page.

Page designer on page 1, the "on close modal1" dynamic action runs a Set Value to set the item P1_VALUE1 to the Dialog Return Item, P2_VALUE.

Summary

To use my special modal page in my application, I need to:

  1. Set a unique Static ID on the region
  2. Add an Edit button with a dynamic action
  3. Add a hidden URL item based on an expression
  4. Add a dynamic action to the region on Dialog Closed

The outcome is that the modal page provides a user-friendly experience involving any complex items, lists, dynamic actions, conditions, etc. maintained in one place, which can be re-used anywhere needed in the application.

If you would like to examine in detail the demo app, you can download it from here: https://apex.oracle.com/pls/apex/jk64/r/demo-reusable-modal/home (click the “Download this demo app” link). You may then install this in your own workspace and check out how it all works.

Have you had a similar requirement in your apps? Comment below and describe how you implemented it.


I didn’t change anything… yet I get “Unsaved changes”?

I had an APEX page based on a Form region that I’d built by hand (rather than using the wizard). I was wondering why the user always got an unexpected warning “Changes that you have made may not be saved.” – even though they hadn’t changed anything on the page.

I found Martin D’Souza’s article How to Find Which Item has Been Changed in APEX and ran the code in the browser console. This pointed me to a single item and I had a closer look at it.

I noticed that the item had a List of Values, and it had the Display Null Value setting set to No; however, the value in the underlying column was NULL. What was happening was that the item could not handle a null value, so it was changing to the first value in the LOV; this in turn marked the item as “changed” which caused the “unsaved changes” warning to show when the user tries to navigate away from the page.

When I set Display Null Value to Yes, the problem was resolved. Alternatively, I could have ensured that the underlying column would always have a value (e.g. by putting a NOT NULL constraint on it), which would also have resolved this problem.


APEX Map Region vs. Google Map Plugin

Within the APEX development team it has been known for some time that maps are frequently required and this has been on the roadmap to be built in to the core product.

Since 2016 I have built and maintained plugins that make it easy to integrate Google Maps in your APEX applications. The most popular of these is the ReportMap Plugin which has received a wealth of features and enhancements, and is being used widely.

Introducing: Map regions

In the latest pre-production release APEX 21.1 which you can try today for yourself at apex.oracle.com, the APEX development team has introduced the new Map region. This component allows the developer to show a world map on the page, and add one or more “Layers”, each based on a table or SQL query, to show features on the map.

This is a welcome move because it means maps will be easy for all APEX developers to use, including those who avoid plugins (e.g. due to the lack of direct support from Oracle). It also means that maps added to applications based on the core feature will be fully supported in future releases of APEX without needing to rely on a 3rd party.

Note: this post is based solely on my first impressions of the new feature and is not intended to answer all questions about it. There will be more official blog posts coming directly from the APEX development team about this and other new features being introduced in APEX 21.1, so keep a look out for those!

The APEX Map region renders the map using the MapBox API, with a number of tile backgrounds included based on OpenStreetMap and HERE map data.

Implementing a Map Region

Let’s try the new Map region, and compare it to the jk64 ReportMap plugin. To add a map to a page, I added a region of type “Map” and nominated a data source for the Layer to show on it.

First thing you might notice is what I didn’t need:

  • no 3rd party plugin to install
  • no account on a 3rd party cloud service
  • no API key, and no APIs need to be enabled
  • no credit card details

The Map region is free to use within your applications, just like any other built-in feature of APEX.

If you already have a map based on the ReportMap plugin, you can if you wish convert it to a map by simply changing the region Type to Map – the SQL data source will be preserved and you can use the same query for the new Map region type. However, the danger with this approach is that you may lose some attributes and customisations that you had on the plugin region. Instead, I recommend using the Duplicate feature to create a copy of your map region, change the attributes on the copy, using the original as a reference as you go. Once you’re happy with the new map you can then delete the original plugin region.

You can choose to set the data source directly on each Layer (e.g. if you want to get data from multiple data sources), or you can set the data source on the map Region. If you set it on the Region, each Layers may refer to the Region data source by setting the layer’s Location attribute to Region Source.

If you have a single data source that you want to split up into multiple Layers, you can set the Row Assignment column which will be used to differentiate the data for each layer. This would be more efficient than adding separate SQL queries for each layer if the queries are based on the same table or view.

The first thing I noticed when converting my demo application was that since my data source was based on an APEX collection, the Lat and Lng columns are strings, not numbers; to use this as a data source for the Map region I had to convert the strings to numbers first using TO_NUMBER.

Once that was done, I could map the LAT and LNG columns to the layer by setting the Geometry Column Data Type to Longitude/Latitude:

Notice that the layer may alternatively be based on a SDO_GEOMETRY column, or a GeoJSON geometry object.
Layer attributes

This is the result:

I wanted to style it as close as possible to my plugin demo so I tweaked a few attributes on the Region:

  • Appearance / Template Options / Remove Body Padding = on
  • Region Attributes:
    • Background = Custom
    • Standard (tile background) = Oracle World Map
    • Height = 350
    • Controls / Options / Mousewheel Zoom = on
    • Legend / Show = off
  • Layer Attributes:
    • Point Objects / Shape Scale = 1.5
    • Appearance / Fill Color = #e21818 (reddish)
    • Tooltip / Column = NAME
    • Info Window / Title Column = NAME
    • Info Window / Body Column = INFO

Much nicer colours, in my humble opinion 🙂

Map Dynamic Actions

The next thing I need to do is handle click events on the pins. To do this, I added a Dynamic Action to the map region, on the event Map Object Clicked.

Notice that the Map region can trigger the following events:

  • Map Initialized – the map has loaded, including all the data
  • Map Changed – the user pans the map or zooms in or out
  • Map Clicked – the user clicks in the map area (but not on a pin)
  • Map Object Clicked – the user clicks on a pin

Whenever I’m experimenting with dynamic actions one of the first things I’ll add is a Action to run this JavaScript:

At runtime in debug mode, the console log will then show the content of this.data which shows the structure it takes.

Based on this, I can see that we get the id, infoWindow, lat, lng, and tooltip attributes – similar to the structure provided by the ReportMap plugin events. If I want to display the Latitude and Longitude values on the page, I create a display-only item (e.g. P1_POSITION), and add a “Set Value” action to the dynamic action as follows:

When a pin is clicked, we now see this data on the page:

Of course, we could make this item hidden if we want, and use its value in other ways.

The Map Clicked event returns this.data.lat and this.data.lng to indicate where the user clicked.

The Map Changed event returns:

  • this.data.changeType – e.g. ‘map-resized’, ‘map-drag’, ‘map-zoom’
  • this.data.bbox – bounding box, an array of numbers of longitudes and latitudes [west, south, east, north]
  • this.data.layers – an array with attributes for each layer (id, name, visible)
  • this.data.bearing
  • this.data.pitch
  • this.data.zoom

New Features

The following is a short list of features or enhancements that the new Map region has, which are not (currently) supported by the ReportMap plugin:

  • Multiple data layers, each with their own distinct data source; you can also use one SQL query for multiple layers if you want
  • REST data sources
  • Declarative styles – options for customing how each data layer is rendered, including pin and feature icon, colour and size
  • Min/Max Zoom – each layer can be shown or hidden automatically depending on the zoom level (e.g. show a more detailed layer as the user zooms in)
  • Legend – each data layer (optionally) can be shown in a legend, allowing the user to selectively show/hide each layer
  • Extruded polygons – show a 3D polygon rising from the ground with the height determined by a column from your data source
  • Initial Position and Zoom is remembered between page requests
  • Circle tool – allows the user to draw a circle on the map; you can then respond to this by filtering data by points that fall within the circle
  • Distance tool – allows the user to calculate the distance between two points

Conclusion

That’s page 1 of my side-by-side demo done. Not too shabby!

Only 34 other pages to go over… eventually I plan to release my demo application for you to play with. Some of the demo pages will not be so easy or even possible to replicate, however, until we get the ability to use the Google Maps JavaScript API in the native Map region – so they’ll need to wait for some potential future release.

More posts to come…

Q: Should we switch now, or wait?

If you have a simple map on your page showing some pins, with no custom JavaScript code that provide specific custom behaviour, I think you should consider switching now. Of course, you should make sure to test the new region thoroughly – as with any major new feature, there will be a few bugs here and there. Overall however the Map region looks solid so far and is based on a well-known open source API with a long history.

One of the things to remember if you’re planning to switch from the ReportMap plugin to the new Map region is that not every feature is implemented the same way, and some features are not available at all (at least, not yet, if ever). This is partly because they are based on different JavaScript APIs (Google Maps vs MapBox). In addition, some UI behaviour is different and will likely always be different, although a lot of it will be customisable.

Q: Is this the end for the JK64 ReportMap plugin?

No, the ReportMap plugin is not going away any time soon. I plan to enhance and support it for years to come. My intent is to continue supporting the plugin at least until the APEX Map component supports integration of the Google Maps JavaScript API, and provides declarative support for most (ideally, all) of the declarative features of the ReportMap plugin. I expect that after this, most developers will naturally choose the native Map region over the plugin for new projects, and I’ll only need to provide bug fix support for the plugin while existing users of the plugin migrate gradually to the new component.

I consider this one of the strengths of the plugin system: the APEX development team will never have the capacity to support every last feature needed for every last application built for any customer in the world, so developers and companies should be empowered to create and use plugins to fill those gaps.

These plugins often serve to prove there is demand and need for a particular feature, and this often prompts the APEX development team to consider building these features into the core product, making it better with each release. Exciting times are ahead of us.


Pretty Print JSON in PL/SQL

I have been working with some code that uses JSON, sometimes fairly large documents of the stuff, and it’s often necessary to send this to the debug log (e.g. DBMS_OUTPUT) for debugging; however, the builtin functions that convert a JSON object to a string (or clob) return the JSON document in one big long line, like this:

{"surname":"Jones","name":"Bob","age":42,"alive":true,"children":[{"name":"Sally","age":10},{"name":"Terrance","age":8},{"name":"Ulyses","age":6}]}

To show this formatted, I added the following function using JSON_SERIALIZE with the “PRETTY” option, to my utility package:

function format_json (p_clob in clob) return clob is
    l_blob blob;
    l_clob clob;

    function clob_to_blob(p_clob clob) return blob is
        l_blob blob;
        o1 integer := 1;
        o2 integer := 1;
        c integer := 0;
        w integer := 0;
    begin
        sys.dbms_lob.createtemporary(l_blob, true);
        sys.dbms_lob.converttoblob(l_blob, p_clob, length(p_clob), o1, o2, 0, c, w);
        return l_blob;
    end clob_to_blob;

begin
    l_blob := clob_to_blob(p_clob);
    select JSON_SERIALIZE(l_blob returning clob PRETTY) into l_clob from dual;
    return l_clob;
end format_json;

Note that my function takes a CLOB, not a JSON object, because sometimes I receive the data already as a CLOB and I don’t want to require conversion to JSON before passing it to my formatting function.

Now, when I call this function:

declare
    l_json     json_object_t := json_object_t();
    l_children json_array_t := json_array_t();
    l_clob     clob;
begin
    l_json.put('surname','Jones');
    l_json.put('name','Bob');
    l_json.put('age',42);
    l_json.put('alive',true);
    l_children.append(json_object_t('{"name":"Sally","age":10}'));
    l_children.append(json_object_t('{"name":"Terrance","age":8}'));
    l_children.append(json_object_t('{"name":"Ulyses","age":6}'));
    l_json.put('children',l_children);
    l_clob := l_json.to_clob;
    l_clob := utility_pkg.format_json(l_clob);
end;

I get the following result:

{
  "surname" : "Jones",
  "name" : "Bob",
  "age" : 42,
  "alive" : true,
  "children" :
  [
    {
      "name" : "Sally",
      "age" : 10
    },
    {
      "name" : "Terrance",
      "age" : 8
    },
    {
      "name" : "Ulyses",
      "age" : 6
    }
  ]
}

Comparing Timestamps with Time Zone

If you break out into a sweat reading the title, it probably means that like me, you have had too little exposure to working with timestamps in Oracle.

(meme pretending that Gordon Ramsay says "I hate timezones ... in all timezones")

Until recently I never really had much to do with time zones because I lived in the (now even moreso, due to covid) insular state of Western Australia. In WA most places pretend that there is no such thing as time zones – so our exposure to Oracle data types is limited to simple DATEs and TIMESTAMPs, with nary a time zone in sight. We just set the server time zone to AUSTRALIA/Perth and forget it.

Now I’ve helped build a system that needs to concurrently serve the needs of customers in any time zone – whether in the US, in Africa, or here in Australia. We therefore set the server time zone to UTC and use data types that support time zones, namely:

  • TIMESTAMP WITH TIME ZONE – for dates and times that need to include the relevant time zone;
    and
  • TIMESTAMP WITH LOCAL TIME ZONE – for dates and times of system events (e.g. record audit data) that we want to always be shown as of the session time zone (i.e. UTC), and we don’t care what time zone they were originally created in.

A colleague came to me with the following issue: a business rule needed to check an appointment date/time with the current date; if the appointment was for the prior day, an error message should be shown saying that they were too late for their appointment. A test case was failing and they couldn’t see why.

Here is the code (somewhat obfuscated):

if appointment_time < trunc(current_time) then
    :p1_msg := 'This appointment was for the previous day and has expired.';
end if;

We had used TRUNC here because we want to check if the appointment time was prior to midnight of the current date, from the perspective of the relevant time zone. The values of appointment_time and current_time seemed to indicate it shouldn’t fail:

appointment_time = 05-MAR-2021 07.00.00.000000 AM AUSTRALIA/Perth
current_time     = 05-MAR-2021 06.45.00.000000 AM AUSTRALIA/Perth

We can see that the appointment time and current time are in the same time zone, and the same day – so the tester expected no error message would be shown. (Note that the “current time” here is computed using localtimestamp at the time zone of the record being compared)

After checking that our assumptions were correct (yes, both appointment_time and current_time are TIMESTAMP WITH TIME ZONEs; and yes, they had the values shown above) we ran a query on the database to start testing our assumptions about the logic being run here.

select
    to_timestamp_tz('05-MAR-2021 07.00.00.000000 AM AUSTRALIA/Perth') as appt_time,
    to_timestamp_tz('05-MAR-2021 06.45.00.000000 AM AUSTRALIA/Perth') as current_time
from dual

APPT_TIME    = '05-MAR-2021 07.00.00.000000000 AM AUSTRALIA/PERTH'
CURRENT_TIME = '05-MAR-2021 06.45.00.000000000 AM AUSTRALIA/PERTH'

So far so good. What does an ordinary comparison show for these values?

with q as (
    select
        to_timestamp_tz('05-MAR-2021 07.00.00.000000 AM AUSTRALIA/Perth') as appt_time,
        to_timestamp_tz('05-MAR-2021 06.45.00.000000 AM AUSTRALIA/Perth') as current_time
    from dual)
select
    q.appt_time,
    q.current_time,
    case when q.appt_time < q.current_time then 'FAIL' else 'SUCCESS' end test
from q;

APPT_TIME    = '05-MAR-2021 07.00.00.000000000 AM AUSTRALIA/PERTH'
CURRENT_TIME = '05-MAR-2021 06.45.00.000000000 AM AUSTRALIA/PERTH'
TEST         = 'SUCCESS'

That’s what we expected; the appointment time is not before the current time, so the test is successful. Now, let’s test the expression actually used in our failing code, where the TRUNC has been added:

with q as (
    select
        to_timestamp_tz('05-MAR-2021 07.00.00.000000 AM AUSTRALIA/Perth') as appt_time,
        to_timestamp_tz('05-MAR-2021 06.45.00.000000 AM AUSTRALIA/Perth') as current_time
    from dual)
select
    q.appt_time,
    q.current_time,
    trunc(q.current_time),
    case when q.appt_time < trunc(q.current_time) then 'FAIL' else 'SUCCESS' end test
from q;

APPT_TIME           = '05-MAR-2021 07.00.00.000000000 AM AUSTRALIA/PERTH'
CURRENT_TIME        = '05-MAR-2021 06.45.00.000000000 AM AUSTRALIA/PERTH'
TRUNC(CURRENT_TIME) = '03/05/2021'
TEST                = 'FAIL'

Good: we have reproduced the problem. Now we can try to work out why it is failing. My initial suspicion was that an implicit conversion was causing the issue – perhaps the appointment date was being converted to a DATE prior to the comparison, and was somehow being converted to the UTC time zone, which was the database time zone?

with q as (
    select
        to_timestamp_tz('05-MAR-2021 07.00.00.000000 AM AUSTRALIA/Perth') as appt_time,
        to_timestamp_tz('05-MAR-2021 06.45.00.000000 AM AUSTRALIA/Perth') as current_time
    from dual)
select
    q.appt_time,
    q.current_time,
    cast(q.appt_time as date),
    cast(q.current_time as date)
from q;

APPT_TIME                  = '05-MAR-2021 07.00.00.000000000 AM AUSTRALIA/PERTH'
CURRENT_TIME               = '05-MAR-2021 06.45.00.000000000 AM AUSTRALIA/PERTH'
CAST(APPT_TIME AS DATE)    = '03/05/2021 07:00:00 AM'
CAST(CURRENT_TIME AS DATE) = '03/05/2021 06:45:00 AM'

Nope. When cast to a DATE, both timestamps still fall on the same date. Then I thought, maybe when a DATE is compared with a TIMESTAMP, Oracle first converts the DATE to a TIMESTAMP?

with q as (
    select
        to_timestamp_tz('05-MAR-2021 07.00.00.000000 AM AUSTRALIA/Perth') as appt_time,
        to_timestamp_tz('05-MAR-2021 06.45.00.000000 AM AUSTRALIA/Perth') as current_time
    from dual)
select
    q.appt_time,
    q.current_time,
    cast(trunc(q.current_time) as timestamp with time zone),
    case when q.appt_time < trunc(q.current_time) then 'FAIL' else 'SUCCESS' end test
from q;

APPT_TIME                              = '05-MAR-2021 07.00.00.000000000 AM AUSTRALIA/PERTH'
CURRENT_TIME                           = '05-MAR-2021 06.45.00.000000000 AM AUSTRALIA/PERTH'
CAST(TRUNC(CURRENT_TIME) AS TIMESTAMP) = '05-MAR-2021 12.00.00.000000 AM +00:00'
TEST                                   = 'FAIL'

Ah! Now we can see the cause of our problem. After TRUNCating a timestamp, we have converted it to a DATE (with no timezone information); since Oracle needs to implicitly convert this back to a TIMESTAMP WITH TIME ZONE, it simply slaps the UTC time zone on it. Now, when it is compared with the appointment time, it fails the test because the time is 12am (midnight) versus 7am.

Our original requirement was only to compare the dates involved, not the time of day; if the appointment was on the previous day (in the time zone relevant to the record), the error message should appear. We therefore need to ensure that Oracle performs no implicit conversion, by first converting the appointment time to a DATE:

with q as (
    select
        to_timestamp_tz('05-MAR-2021 07.00.00.000000 AM AUSTRALIA/Perth') as appt_time,
        to_timestamp_tz('05-MAR-2021 06.45.00.000000 AM AUSTRALIA/Perth') as current_time
    from dual)
select
    q.appt_time,
    q.current_time,
    case when cast(q.appt_time as date) < trunc(q.current_time) then 'FAIL' else 'SUCCESS' end test
from q;

APPT_TIME                              = '05-MAR-2021 07.00.00.000000000 AM AUSTRALIA/PERTH'
CURRENT_TIME                           = '05-MAR-2021 06.45.00.000000000 AM AUSTRALIA/PERTH'
TEST                                   = 'SUCCESS'

Our logic therefore should be:

if cast(appointment_time as date) < trunc(current_time) then
    :p1_msg := 'This appointment was for the previous day and has expired.';
end if;

It should be noted that if the tester had done this just an hour later in the day, they would not have noticed this problem – because Perth is +08:00, and the timestamps for the test data were prior to 8am in the morning.

Lesson #1: in any system that deals with timestamps and time zones it’s quite easy for subtle bugs to survive quite a bit of testing.

Lesson #2: when writing any comparison code involving timestamps and time zones, make sure that the data types are identical – and if they aren’t, add code to explicitly convert them first.


Some collection methods I’d like to see added to PL/SQL

In building a code generator I found the need to write a number of helper methods for doing basic modifications of arrays that are indexed by integer – such as appending one array onto another, inserting, and shifting. These arrays represent an ordered sequence of strings (e.g. lines of source code).

I think these would be a useful addition to the language if they were made native – e.g. (new commands in UPPERCASE):

declare
    type str_array_type is table of varchar2(32767)
        index by binary_integer;
    l_lines str_array_type;
    l_new str_array_type;
    l_idx binary_integer;
begin
    .. (some code to fill the arrays here) ..

    -- get a subset of lines
    l_new := l_lines.SLICE(50, 59);

    -- extend l_lines with l_new at the end:
    l_lines.APPEND(l_new);

    -- shift l_lines forwards and insert l_new
    -- at the beginning:
    l_lines.PREPEND(l_new);

    -- insert l_new into l_lines at the given index;
    -- shift any existing lines at that location
    -- forward:
    l_lines.INSERT(l_new, at_idx => 21);

    -- remove the given range of indices from
    -- l_lines, replace with whatever is in l_new:
    l_lines.UPDATE(l_new,
        from_idx => 120,
        to_idx   => 149);

    -- apply the given substitution on each line
    l_lines.REPLACE_ALL(
        old_val => 'foo',
        new_val => 'bar');

    -- shift the given range of lines by the given
    -- offset (raise exception if existing data
    -- would get overwritten):
    l_lines.SHIFT(
        from_idx => 20,
        to_idx   => 29,
        offset   => 1000);

    -- shift and renumber all indices in the array
    -- with the given starting index and increment:
    l_lines.RENUMBER(start_idx => 10, increment => 10);

    -- make the array contiguous (i.e. remove gaps):
    l_lines.RENUMBER;

    -- loop over every line in the array that contains
    -- the given string:
    l_idx := l_lines.FIND_NEXT(contains => 'hello');
    loop
        exit when l_idx is null;
        .. do something with l_lines(l_idx) ..
        l_idx := l_lines.FIND_NEXT(contains => 'hello',
            from_idx => l_idx);
    end loop;
end;

I’ve illustrated these with a little sample package that may be viewed here:

https://github.com/jeffreykemp/sample/tree/master/str_array_pkg

What do you think?


ReportMap Release 1.5

The latest version of the ReportMap APEX plugin is now v1.5.

The plugin now supports Overlays, which allows you to add almost any arbitrary HTML or image content to particular points on the map. For example, instead of showing the default red pin, you might want to show a pretty Information card at a location. The cards are clickable as well, and you can use a dynamic action to make your app respond however you wish.

You can even show an image as a map overlay, which will be scaled automatically as the user zooms and pans the map.

In the previous release I added a companion Dynamic Action “Action” plugin that allows you to declaratively perform actions on the map. This release fixes a few bugs in that plugin, and also adds a new, second companion Dynamic Action plugin: Show Directions. This plugin allows you to invoke the Directions API on the map between one location and a destination without needing to write JavaScript. The locations may be specified with static values (lat,lng coordinates or addresses), from items on your page, JavaScript expressions, or jQuery selectors. The travel mode (e.g. driving, bicycling, etc.) can also be specified the same way.

You can review the full list of changes and download the plugin from here: https://github.com/jeffreykemp/jk64-plugin-reportmap/releases/tag/v1.5