Lab 3: A Real Application

 

 

Introduction

 

This week you will turn your site into a real application!  The key is adding backend server support with a database.

 

Instructions:

 

  1. Copy your Lab02 files to a new Lab03 directory. Your main file should still be called index.html

2.      Here is what you what you want to have when you are finished.  Suggested plan of attack for getting there is below:

    1. Note: if you have a compelling case to modify the requirements based on your site, discuss with the instructor in advance.  Normally, requests for a substantive change should be made before the end of the lab period when the lab begins.
    2. There should be some way for the user to add new “things” to your database.  These could be people, books, races, whatever, but there should be at least 2-3 different "attributes" associated with each one (e.g., name, address, and phone).
    3. Adding the new things should be done via AJAX (you’ll probably use a <form>, but it shouldn’t really submit the form to the server – use AJAX instead).
    4. There should be at least two different ways to query info from the database to display in your main page. For instance, you might have an option to search for people, then each person is clickable for more details.  Most likely, this should be the two interactions you used for Lab02, but it can change.  More specific requirements:
      1. Note: the words “query” and “interaction” are used interchangeably here.
      2. You can use either XML or text for the data, but at least one query must be asynchronous.
      3. Both queries must use AJAX.
      4. The two queries must fetch different kinds of things. For instance, one could fetch a list of items (with ID’s and names), and one could then fetch the details for that item.  But one query to fetch item #23 and another to fetch item #87 does not count as two distinct queries.
      5. At least one of these queries need to fetch data that was stored in the “adding new things” step above (this also lets you verify that the “adding new things” part works!)
      6. At least one of the queries must be based on a value that user enters in a search box OR at least one query must be based on something the user clicks, where clicking on different elements yields different results (e.g. clicking on “Fred” vs. clicking on “Wilma”).
      7. If the user clicks twice on something, the page should not display the same information twice. So if the user clicks a button to get a list of items, then clicks again, be sure to delete the old list before you insert the new list.
    5. As always, your code must be commented!
    6. You may use PHP or Perl.  Examples given are in Perl.
    7. In your default.htm page, under “Lab3” include:
      1. A link to Lab03/index.html
      2. Brief user instructions (aimed at the instructor) explaining how to see your interactions (what to click on, enter, etc. – make it easy to see that you have earned full credit!)
  1. Suggested plan of attack (see also helpful info at end)
    1. Get password info from the instructor. 
    2. Plan and create the database table(s) you will need (use MySQL administrator tool – also see helpful info below).
    3. Insert some dummy data into the tables for testing.
    4. Write your Perl program to query the database. Test this via the command line, then via entering the browser URL, before you attempt to use it from JavaScript. If you don’t know what each of these things is, ask!
    5. Get your first AJAX interaction from last week working, where you replace the static file with the Perl program to read from the database.  At first, the “query” can be hard-coded so that it always returns all the data from the database.
    6. Improve your interaction so that the database results depend on what was clicked or entered in a search box.
    7. Get you second AJAX interaction working.
    8. Implement ability for user to add new data to the database.
    9. If not done already, make clicking a second time doesn’t continue to show old results or an old list.

4.      Ensure your page works with Firefox. Having it work on IE is encouraged but not required.

5.      Ensure all your pages validate and that you have met all requirements.

     

NOTE: all HTML files must validate as XHTML without errors for full credit.  The penalty for a file that does not validate is 10%.

Helpful stuff

  1. As always, the “Error Console” in Firefox is invaluable.
  2. To connect to the database, use something like (password to be provided):
    $databaseHandle = DBI->connect( "dbi:mysql:database=mXXXXXX;host=schooner.cs.usna.edu:3306;user=mXXXXXX;password=TBD" );
  3. Perl is easier to debug via the windows command line.
    Here is what to do:
            Click Start, select “Run…”, then type in “cmd” and hit return.
            Enter “W:” and hit return, to change to your web drive
            Enter “cd Lab03” and hit return.
            Proceed with the directions below.
    You should first check for syntax errors by just “checking” the file:
         perl –c -w myquery.pl
    Once that works run it for real:
         perl -w myquery.pl
    If needed, you can provide CGI arguments like this:
         perl –w myquery.pl “query=dogs&type=2”
  4. On the command line, database errors will usually appear automatically.  From the browser, they won’t – instead insert this as a debug:
         print $DBI::errstr;
  5. Do not use the die() function alone – the error it generates can’t be seen from your web page.
  6. Useful SQL examples:
    1. CREATE TABLE comments (USER_NAME VARCHAR(20), TIMESTAMP DATETIME, COMMENT MEDIUMTEXT, PAGE INTEGER);
    2. INSERT INTO comments (USER_NAME, TIMESTAMP, COMMENT, PAGE) VALUES ('Jamie', '2006-09-27 11:30:00', 'hi', 2);
    3. CREATE TABLE topics (TOPIC VARCHAR(20), OWNER VARCHAR(20));
    4. INSERT INTO topics (TOPIC, OWNER) VALUES ('Cars', ‘Jamie’);
    5. Note: ID is automatically created with the table, no need to specify it.

Deliverables

1)      All of your files for Lab03 should be in a folder called "Lab03" (without the quotes) on the Web drive.

2)      Your main page for Lab03 should be called "index.html" (without the quotes) and placed inside the folder Lab03.

3)      Your instructor will assume that your web pages are viewable at http://www.mXXXXXX.it452.cs.usna.edu/Lab03/index.html where XXXXXX is your alpha number. You should check that this URL is viewable and that everything works correctly from a computer where somebody else is logged in. If you've goofed and linked to a file on your X drive, this will help you catch it!

4)      All files must be complete and saved to your Web drive before you submit the hardcopy of your assignment. Do NOT modify your files after you have submitted your assignment.

5)      Turn in the following hardcopy on or before the due date, stapled together in the following order (coversheet on top):

a)      A completed assignment coversheet.  Your comments will help us improve the course.

b)      The first page of the output of the W3C validator, as run on the final version of your Lab03/index.html.  This should show that your document correctly validated, but turn it in anyway if you can’t get your page to validate. 

c)      A printout of the source to your Lab03/index.html file (not the rendered page that you normally see with Internet Explorer/Firefox).   Truncated lines are not acceptable – use Crimson Editor vice Notepad if needed for printing.  You could also paste into Microsoft Word etc. if needed.

d)      Printouts of external JavaScript files, if any.

e)      Printout of the source of the Perl/PHP files that you use.

 

Addenda

1)      XML is great, but can be a little trick to get working.  If you choose to use XML, here are some tips:

a)      You should *not* have a call like:
     print header();
Instead, you want:
     print "Content-type: text/xml; charset=UTF-8\n\n";

b)      To be a valid XML document, there must be a “root” element that surrounds all the other elements. So, if you have 3 <person> elements, put something like a <results> element around all of them.

c)      Before trying to get your Perl-generated XML to work via Javascript and AJAX, first use Firefox (the XML check doesn’t reliably work in IE!) and just run the Perl script via typing the URL into the browser address bar (with arguments if needed).  Check to make sure you have something like this:

Notice that the browser is automatically formatting the XML in a “XML tree” view, with little minus signs next to some elements (you can click on these to collapse it). If you don’t get this, then something is wrong! (a warning about no “style information” is fine).  If you don’t see this, check that the “Content-type” header is correct and that you have a single root element. For instance, here is what you get if you header is wrong (text/plain instead of text/xml):

Or, if you don’t have a single root element, you might get an error like this:



2)      Dealing with those “anonymous functions” can be tricky. In particular, suppose you were creating a table row, and you wanted each cell to pop up the current cell number (cell 1, cell 2, etc.) when you click on it.  You might make code that looked like this:

        for (var i =0; i < elems.length; i++) {
           // Create the <td>
           newTD = document.createElement("td");
           newTD.innerHTML = elems[i];
           newTD.onclick   = function() {window.alert ("Hi, this is cell "+i) };
 
           // Add it to the row
           newTR.appendChild(newTD);   
        }
This code looks good but will not work properly.  Instead, the alert message will be the same (Hi, this is node 5) regardless of what cell you click on.  The reason is that when you use function() to create the anonymous function, it creates a “closure” that wraps-up the variables that are currently in scope.  Each one of these closures that is created all refer to the same variable ‘i’.  So when the code actually executes (when someone clicks on the cell), the ‘i’ value that is used is the value of ‘i’ that was set during the last iteration.  Solution? First, make a new function as follows:
        function makeMyEventHandler(num) {
               return function() {window.alert("Hi, this is cell "+i)};
        }
Note that this a function that returns a function. Then change part of the loop body to be this:
       newTD.onclick   = makeMyEventHandler(i); // Yes, parentheses here!
Why does this work?  Well, when you call makeMyEventHandler(), you are creating a new scope.  The value of ‘i’ is copied into ‘num’.  Because a new copy of ‘num’ is made every time the function is called, each cell gets its own separate copy to reference.
 
It’s worth reading this one more time – this issue comes up more often than you might think.