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webOS HTML5 Database Storage Tutorial

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webOS HTML5 Database Storage Tutorial
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webOS skill level: Beginner
Technologies covered: HTML5, SQL, Javascript
Prerequisite knowledge: Intermediate-level HTML, CSS, and Javascript

With the release of Chapter 1 of Palm webOS by O'Reilly, Palm has confirmed that local storage will indeed be handled by HTML5's new local storage functionality.

If you haven't been able to find any tutorials on HTML5's storage capability, you're not alone.  After looking around, we realized that the HTML5 spec is still at such an early revision that there are few resources out there that describe how it should be used.  But with a little digging, we found this excellent little HTML5 database application over at webkit.org.  We eagerly grabbed the source code, deconstructed it, and we're proud to bring you the first webOS / HTML5 database storage tutorial!  

While we (obviously) haven't tested this application on an actual webOS device, we feel that there's a good chance it would work as-is in the Pre's web browser, as the Pre's browser is webkit-based (although whether the drag & drop functionality would work without modification is unclear at this point).  Check out the end of this article for notes on how we might turn this web-based application into a native application that you could launch from the Pre's launcher screen.

Let's start from the top, shall we?  First of all, if you haven't seen the application yet, try it out here.  Get a good feel for how it behaves, then come back here and dive into the code.

<!doctype html>
<html manifest="DatabaseExample.manifest">
  <head>
    <title>WebKit HTML 5 SQL Storage Notes Demo</title>
    <style>

Right off the bat we find a new HTML5 attribute in the html tag.  The html manifest attribute gives the address of the document's application cache manifest.  There's a very technical explanation of an application cache here, but I'm going to surmise that it's basically a set of cached resources associated with a particular application, and the manifest describes the contents of that application.  Next comes:

body {
    font-family: 'Lucida Grande', 'Helvetica', sans-serif;
}

.note {
    background-color: rgb(255, 240, 70);
    height: 250px;
    padding: 10px;
    position: absolute;
    width: 200px;
    -webkit-box-shadow: 0px 5px 10px rgba(0, 0, 0, 0.5);
}

.note:hover .closebutton {
    display: block;
} 

.closebutton {
    display: none;
    background-image: url(deleteButton.png);
    height: 30px;
    position: absolute;
    left: -15px;
    top: -15px;
    width: 30px;
}

.closebutton:active {
    background-image: url(deleteButtonPressed.png);
}

.edit {
    outline: none;
}

.timestamp {
    position: absolute;
    left: 0px;
    right: 0px;
    bottom: 0px;
    font-size: 9px;
    background-color: #db0;
    color: white;
    border-top: 1px solid #a80;
    padding: 2px 4px;
    text-align: right;
}

Nothing particularly new here; some styles that get applied to elements of the document, including a webkit-specific style declaration -webkit-box-shadow that will theoretically work on the Pre because it uses a webkit-based browser.  Now to the interesting stuff:

var db;

try {
    if (window.openDatabase) {
        db = openDatabase("NoteTest", "1.0", "HTML5 Database API example", 200000);
        if (!db)
            alert("Failed to open the database on disk.  This is probably because the version was bad or there is not enough space left in this domain's quota");
    } else
        alert("Couldn't open the database.  Please try with a WebKit nightly with this feature enabled");
} catch(err) { }

Let's break this down even further and look at what each line is doing:

try {
    if (window.openDatabase) {
    ...
    } else
        alert("Couldn't open the database.  Please try with a WebKit nightly with this feature enabled");
} catch(err) { }

These enclosing statements are attempting to determine whether the window object of the current browser (or, in our case, version of webOS) supports the the HTML5 openDatabase method. The try statement will catch an error if the any of the statements enclosed cause the interpreter to throw an error.  

If you're developing for the Pre or another webOS device, you may decide to leave checks like these out to minimize the size of your application, but they can also provide valuable debugging information if your application is not behaving as you expect.

        db = openDatabase("NoteTest", "1.0", "HTML5 Database API example", 200000);
        if (!db)
            alert("Failed to open the database on disk.  This is probably because the version was bad or there is not enough space left in this domain's quota");

Here we're calling a new HTML5 window method openDatabase.  This method returns a database object, which we are assigning to the variable "db".  The openDatabase method takes 4 arguments:

  1. database name
  2. database version
  3. display name
  4. estimated size, in bytes of the data that will be stored in the database

In this case, the database name is NoteTest, the version is 1.0, the database display name is HTML5 Database API example and the size of the data is 200kb (approximately; 1kb=1024bytes).  The database name parameter specifies the name you will use to reference the database in the code, and the display name is probably how the database will be displayed in some sort of database browser that might be bundled with HTML5 compatible browsers.

Next, we get into the fun stuff!



 

18 Comments

Feed
  1. Really bad tutorial, the subject, the HTML 5 databse, is drowning in a load of unrelated code. Any code not strictly related to the topic should be keept to a minimum.
  2. Couldn't agree more with Jacob C.M.A.
  3. Contrary to the other comments left above ^ I thought this tutorial was well thought out and well executed. It covered the basics as well as some advanced techniques for working with HTML5 databases.

    The above comments are clearly the product of uneducated users. If they understood HTML5 db's and the webOS they would know that javascript (that so called "unrelated code") does everything as far as the database interaction and user interaction goes and therefore is, not only related, but necessary to make proper use of the database structure and apply it to both the webOS platform and the web in general.

    Kudos to Mr. Ken Young for a great tutorial, I have learned many new things from this article and appreciate the time he took to write it. Also, I apologize for the aforementioned flaming of users, though quite rude I deemed it necessary in order to maintain my sanity and vent some frustration...
  4. Though this is hardly worth being called a "tutorial" and has very little to do with WebOS, it is interesting to read. I also tried just copy-pasting the complete HTML from the webkit app in a WebOS SDK application, simply in the index.html, and it works. Kindof. Can't create new notes, but the one note works.
  5. Unfortunately, this is not a tutorial. In my opinion, this is just a copy and paste off of webkit Sticky Notes Demo. There is nothing here that documents any HTML 5 Database methods and usage. And to make it worse you call it aq "Web OS" tutorial? Like you said it yourself, you haven't even tried WebOS
  6. Hi
    is there any import files such as jar or any files for using html5 Palm WebOS. ?

    where will use the above code

    var db;

    try {
    if (window.openDatabase) {
    db = openDatabase("NoteTest", "1.0", "HTML5 Database API example", 200000);
    if (!db)
    alert("Failed to open the database on disk. This is probably because the version was bad or there is not enough space left in this domain's quota");
    } else
    alert("Couldn't open the database. Please try with a WebKit nightly with this feature enabled");
    } catch(err) { }

    html file or js file..?
    how to call and access database connection ..?
    is there any sample application plz send me some samples...
  7. How about updating this? Ken, your note at the end said you are going to do that....I'd love to see it. Thanks!
  8. I think that the tutorial explains properly the webstorage standard, thanks for it, also i have just one question, where is the database stored ? could i copy it to other place with the webkit enabled ?

    is possible to access the temporally database and copy to other place?

    thanks
  9. I really liked this tutorial. It helped me understand how to make a database work. I have a couple recomendations for the author:
    you left out just a couple of lines that a beginner might not see that you left out. By the way the code at the beginner was placed it was not clear that you need this between the styles and the javascript at the beginning:


    and also left this out at the end before the paragraph:



    plus 2 more lines:


    I would like to know what the tx is that is being passed in this part:
    db.transaction(function(tx) {
    it is not clear from the tutorial.
    also explain what this line means:
    if (!("_saveTimer" in this))
    it looks for a method called _saveTimer attached to self ( or this )
    everything else made sense. And what does this mean:
    ++highestZ;
    I would guess that it does the same as highestZ++; I just never knew you could reverse it.
    Thanks for the great lesson on html5!
  10. remove the coment that is above. It was a mistake because i needed to encode the html.
    I really liked this tutorial. It helped me understand how to make a database work. I have a couple recomendations for the author:
    you left out just a couple of lines that a beginner might not see that you left out. By the way the code at the beginner was placed it was not clear that you need this between the styles and the javascript at the beginning:


    and also left this out at the end before the paragraph:



    plus 2 more lines:


    I would like to know what the tx is that is being passed in this part:
    db.transaction(function(tx) {
    it is not clear from the tutorial.
    also explain what this line means:
    if (!("_saveTimer" in this))
    it looks for a method called _saveTimer attached to self ( or this )
    everything else made sense. And what does this mean:
    ++highestZ;
    I would guess that it does the same as highestZ++; I just never knew you could reverse it.
    Thanks for the great lesson on html5!
  11. sorry, remove the 2 posts above so this one should show the html correctly
    I really liked this tutorial. It helped me understand how to make a database work. I have a couple recomendations for the author:
    you left out just a couple of lines that a beginner might not see that you left out. By the way the code at the beginner was placed it was not clear that you need this between the styles and the javascript at the beginning:

    and also left this out at the end before the paragraph:

    plus 2 more lines:


    I would like to know what the tx is that is being passed in this part:
    db.transaction(function(tx) {
    it is not clear from the tutorial.
  12. the comment I was trying to post wouldn't allow me to show any kind of html code so i will leave the angle brackets out. remove all comments above this please.

    I really liked this tutorial. It helped me understand how to make a database work. I have a couple recomendations for the author:
    you left out just a couple of lines that a beginner might not see that you left out. By the way the code at the beginner was placed it was not clear that you need this between the styles and the javascript at the beginning:
    end style tag (no angle bracket because the synax is not allowed here in comments)
    script tag
    and also left this out at the end before the paragraph:
    script tag
    end head tag
    body tag
    plus 2 more lines at the very end of code:
    end body tag
    end html tag

    I would like to know what the tx is that is being passed in this part:
    db.transaction(function(tx) {
    it is not clear from the tutorial.
  13. it won't allow a comment too long so I split it into a second part
    also explain what this line means:
    if (!("_saveTimer" in this))
    it looks for a method called _saveTimer attached to self ( or this )
    everything else made sense. And what does this mean:
    ++highestZ;
    I would guess that it does the same as highestZ++; I just never knew you could reverse it.
    Thanks for the great lesson on html5!
  14. Hey Mike, thanks for the comments and sticking with it even though the comments system doesn't seem to want to allow HTML code. I'll need to look into that, because the ability to post sample code is pretty huge on a site like this.

    I've been way behind updating the site because of other things going on (e.g. getting a job that pays the bills!), but I'm hoping to get back to it soon!
  15. I like window.openDatabase(). A partly-developed demo is at: http://www.thebrentc.net/programs/db.html
  16. Thank you Ken. I feel as though I have been on the far outskirts of the coding vortex for some time now.
    Lately I've felt as if I am closing in on the center, slowly but surely. Your tutorial has given me a hefty nudge in that direction and the broad brush was exactly what I needed.
    You cleared up a number of those 'I think I know, sorta, kinda...' things that have been bugging me.
    Sincerely,
    Michael
  17. OK, this is a fairly terrible "tutorial." It skips vital steps like putting in script tags, it ignores errors if it won't window.openDatabase, over all poor quality.
  18. I think it might be better to create the table using: "CREATE TABLE IF NOT EXISTS table_name". An exception might be thrown for reasons other than the table not existing.

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