Educational Eclipse

Last night around midnight I laid in bed hoping that thousands of people on the other side of the world took the opportunity to experience the once in a life time experience that would be a total solar eclipse.

If you agree that a wonderful piece of prose can help recreate the experience, I recommend this literary non-fiction from 1982 by Annie Dillard.

Today I'd like to share three things I learned about the solar eclipse, considering I'm somewhat of an astronomy geek.

1) Shadow Bands

One of the amazing things about total solar eclipses is because they are relatively rare, there are still phenomena that science is trying to explain.

This video of an eclipse (which I recommend with a little sound) actually shows none of the classic imagery of a solar eclipse, but it captures so much of the awe.



And should I be lucky enough to witness one in future, I would have to ensure I experienced all that's available, even if it meant sticking up some big sheets of paper!

I think I might have a look like that of Katie Mack in the second photo, and probably the third.

2) Gravitational Lensing

In addition to the fact these eclipses are so awe inspiring, they do offer a bit of science, beyond helping calculate the dimensions of the solar system.

This example includes one of my favourite phenomena, more frequently associated with deep space imagery - gravitational lensing.

It turns out when the total eclipse happens, astronomers can take the opportunity to locate stars prominent enough to shine through. Compare distance between stars as observed at night, and astronomers can see how the sun's mass has nudged light, thereby confirming general relativity.
Stunning.

A concise article here with two great images, or google "Eddington 1919 eclipse"

3) Flight of the Concorde

All speeds involved with the eclipse are pretty wild, but back in the 70s, long before SpaceX started landing rockets on sea barges, there was a curious supersonic jet about to go commercial that took the public relations opportunity to fly faster than the speed of sound across Africa to accompany a 1973 eclipse.
Curious Droid - NASA chasing a shadow at 50k feet | Concorde 1973

I've been quite addicted to that channel recently, some great videos to watch during a lunchtime subway.

The first two I learned directly from Skeptoid Episode #584 by Brian Dunning. It's a great 12 minute podcast (now with ads) that I might describe as mixing science with anthropology. Very easy to pick a few interesting topics, then get hooked.

Did you see #Eclipse2017? Did you travel to get there?

Revising jQuery with Oracle APEX

A few years ago I managed to bust out a book that explored my experiences using jQuery within Oracle APEX to solve various problems, many originally explored when building some "backend" apps for use on tablets.

For those who've read my book, thank you and I hope it was useful to you.
(I also hope you read the revised chapter 9 on calling PL/SQL from JavaScript.)
Please let me know what you thought of it with a review on Amazon.

The reason I bring this up is because I was asked on Twitter whether I would do a revision of my book for APEX 5.1.

@swesley_perth do you plan to write 2nd edition of your book "Pro jQuery in Oralce Application Express" to incorporate apex5.1 feature?

— Kevin Zhang (@kzhangkzhang) August 16, 2017

I'm not sure if you've noticed, but my extra-curricular output has been down this year, despite my best intentions. That's not my answer, but it does weigh into what I think about the answer to that question.

Half of that book was written prior to APEX 5.0 being released. While a lot of the content is agnostic to the version of APEX you have, I must admit my techniques have evolved since the advent of the Page Designer.

That's not to say learning how to apply jQuery within APEX isn't useful. Having these fundamentals are still very much applicable, and useful to know when constructing dynamic actions; and even when defining CSS. But I think because it's much quicker to navigate through your dynamic actions in the Page Designer, I think there is less need to bundle logic within a JavaScript block.

I'm not sure revising this particular book for a later version of APEX would add value.

NASA Cassini

My video course had no particular theme and just explored various APEX techniques, hence the name. My book wasn't much different, and if I was going to do something again in future, it would possibly be along the same lines. Or something
even more applied. I do have ideas.

But I've been enjoying an awful lot of science in the time being. So much going on in space news!
It will be sad to see Cassini finish... Don't be surpised, I already have a post in mind for that amazing project. Correction, I already mentioned it during my 2016 blog review. Heck, I might do another anyway.

In Memory Session State - Simple Example

Not too long ago I encountered an interesting behaviour with session state, turns out not long after Dick Dral posted a very similar article that I had not yet seen.

Recently I encountered an even easier scenario.

I had a bunch of columns where I wanted to use the same prefix across all headers, but I wanted to define the value once, referring to it many times. I'm betting on the fact someone may change their mind.

Interactive Report with pivoted data

So I created a hidden item called P222_PREFIX and gave it a static source of "Ch".

Page item source

If I substitute this item as part of the column heading for each column, it will use the value found session state - not the database value, but the value based on the defined source, placed only in memory for the duration of page rendering.

Column heading

So while the output may appear as desired after the page renders, if the region is partially refreshed by hitting "Go" on an interactive report or just triggering region refresh, the prefix will disappear because there is no value for P222_PREFIX in session state once the page finishes rendering.

Desired output

To fix the problem we add a computation on the hidden item to set the value, instead of using a static source. This ensures the value is in session state for current and later usage.

An alternative solution to the task at hand might be to use Shortcuts.

APEX Login Background Image Cover

For a while I've wanted to play with cover photos on login pages, and when Keegan asked a similar question on Twitter, I was curious enough to ultimately have a play.

Someone mentioned relevant a reference to CSS-Tricks Perfect Full Page Background Image, but after quickly finding the video Keegan must have screenshotted in her tweet, I realised us APEX developers need to use the following instead of 'html' as our selector.
.t-PageBody--login

Update for APEX 19.2: Days after I had a discussion about limiting the references to Universal Theme (UT) classes, particularly nested ones. I find that my original extended reference of .t-PageBody--login .t-Body is no longer valid in 19.2 UT.
As Peter suggested, it would be great to have a set of release notes to supplement the living document that is apex.oracle.com/ut.
I possibly wouldn't expect this particular example to be itemised, but knowing where to look would be great.

Plugin extraordinaire Daniel suggests

using 16:9 1920x1080 for standard UT use css media queries for different screen sizes with a pool of 2 / 3 images

The example I applied uses a CSS media query to not use a background image for smaller screens, as it may look too busy.

<style>
@media (min-width:400px)  { /* anything but mobile */
  .t-PageBody--login .t-Body {
    background: url(#IMAGE_PREFIX#cover_images/&P101_IMAGE.) no-repeat center center fixed;
    -webkit-background-size: cover;
    -moz-background-size: cover;
    -o-background-size: cover;
    background-size: cover;
  }
}
</style>

I defined this CSS within a region so I could apply a 'dev only' build option. Alternatively, this could be a PL/SQL region, with the code abstracted/encapsulated within a PL/SQL package, possibly utilising the htp package.

Style within Region

This also means the image location and file name are easily parameterised. So your images could be located anywhere, and you could programmatically decide which image to display. And/or use media queries to determine which image should display on the relevant device.

As an experiment, I wondered if I could rotate through a number of images, so each time someone visited the login page, they would see one image from a pool of many. So I defined an item with the following calculation:
'beauty'||floor(dbms_random.value(1,8))||'.jpg'

We can confirm an evenly distributed calculation by running that computation many times and counting the results.

select count(*), val from (
  select floor(dbms_random.value(1,8)) val
  from dual connect by level < 10000
) group by val

COUNT(*) VAL
1413  1
1445  6
1412  2
1420  5
1411  4
1415  3
1483  7

This would randomly select from a small suite of photos in the folder. I've used a selection I've collected from APOD.

And voila, an inspirational login page.

APEX Login with background cover image

I think an improvement would be to show a consistent image while attempting to login. A brief experiment suggests only running the computation when P101_IMAGE is null, and only clearing login fields (not the entire page cache) during page processing.

This could be the final bling you need after pimping your login page.

Don't forget, you can style the backend login, too.

Once again, thank you #orclapex community for making this a breeze.