Blog Moved

I have moved this blog from here to CodePilgrim. I have copied some of the posts also over there. Please follow me there.

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Change a drop down when other changes in AJAX way

Here we are going to see basic AJAX script in play. Here I’m writing a script which populates a drop down box with states according to the countries selected in another drop down. So let’s see how it is done.

Given below are the drop downs in play (Note: I’ve only used a few data)

Country: <select name="country" onchange="return onchangeajax(this.value);" >
 <option value=""   selected="selected" >Select</option>
 <option value="USA"  >USA</option>
 <option value="India"  >India</option>
 <option value="UK"  >UK</option>
 </select><br />
 State: <div id="statediv"><input type="text" name="state" /></div>
 <input type="submit" name="signupsubmit" value = "Sign Up" />

Now as we see we have written a JavaScript function call on changing the items in drop down. Given below is the Ajax code to be embedded in the page.

function onchangeajax(pid)
 {
 xmlHttp=GetXmlHttpObject()
 if (xmlHttp==null)
 {
 alert ("Browser does not support HTTP Request")
 return
 }

 var url="changestate.php"
 url=url+"?pid="+pid
 url=url+"&sid="+Math.random()
 document.getElementById("statediv").innerHTML='Please wait..<img border="0" src="images/ajax-loader.gif">'
 if(xmlHttp.onreadystatechange=stateChanged)
 {
 xmlHttp.open("GET",url,true)
 xmlHttp.send(null)
 return true;
 }
 else
 {
 xmlHttp.open("GET",url,true)
 xmlHttp.send(null)
 return false;
 }
 }

 function stateChanged()
 {
 if (xmlHttp.readyState==4 || xmlHttp.readyState=="complete")
 {
 document.getElementById("statediv").innerHTML=xmlHttp.responseText
 return true;
 }
 }

 function GetXmlHttpObject()
 {
 var objXMLHttp=null
 if (window.XMLHttpRequest)
 {
 objXMLHttp=new XMLHttpRequest()
 }
 else if (window.ActiveXObject)
 {
 objXMLHttp=new ActiveXObject("Microsoft.XMLHTTP")
 }
 return objXMLHttp;
 }
</script>

Now we see that in the Ajax script it is calling another file ‘changestate.php’. This is the file which has the code that should populated in the ‘statediv’

<?php
 $val=$_REQUEST['pid'];
 if($val == 'USA')
 {
?>
<select name="state">
 <option value="">--Select--</option>
 <option value="Alabama">Alabama</option>
 <option value="Alaska">Alaska</option>
</select>
<?php
 }
 else if($val == 'India')
 {
?>
<select name="state">
 <option value="">--Select--</option>
 <option value="Karnataka">Karnataka</option>
 <option value="Kerala">Kerala</option>
</select>
<?php
 }
 else
 {
?>
<input type="text" name="state" />
<?php
 }
?>

[/sourcecode]

Adding Pagination in PHP

Here is an example of  how to use pagination in your PHP oage. I’m using a pagination class developed by Shiege Iseng’ and can be downloaded from here.

We include this file in the page we use. So here is a basic script that shows the details of users from a database and shows 4 of them in a pagae and shows 3 pages as links in between the [prev] and [next] links.


<?php

//making the database connection
include_once('includes/connection/connection.inc');
 dbConnect();

//including the paging class
 require_once('paging_class.php');

//database query
 $qry = "SELECT * FROM USERS";
 $results = mysql_query($qry);
 $num_rows = mysql_num_rows($results);

//making a paging object that shows 4 results and 3 links
$paging = new paging(4,3);
 $paging->db($host,$username,$passwd,$dbName);
 $paging->query($qry);
?>

<html>
 <head>
 <title>Pagination Example</title>
 </head>

<body>

<table>
 <tr>
 <td>Total Results Found: <?php echo $num_rows; //prints total results ?></td>
 </tr>
 <tr>
 <td>Sl No</td>
 <td>First Name</td>
 <td>Last Name</td>
 <td>Sex</td>
 <td>DOB</td>
 <td>Email</td>
 </tr>

 <?php
 $sl = 1;
 $pageno = 1;
 $pageno = $pageno - 1;
 if($pageno > 0)
 $s1 = $pageno * 10;
 else
 $s1 = 0;
 ?>

 <?php
 if($num_rows > 0)
 {
 $i = 1;
 while($obj=$paging->result_assoc())
 {
 $s1 = $s1 + 1;
//to alternate b/w colors in the row
 if(($i + 1) % 2 == 0)
 $bgcolor="#dbe3f0";
 else
 $bgcolor="#dbdcf0";
 ?>

 <tr bgcolor="<?php echo $bgcolor?>">
 <td><?php echo $sl; ?></td>
 <td><?php echo $obj['firstname']; ?></td>
 <td><?php echo $obj['lastname']; ?></td>
 <td><?php echo $obj['sex']; ?></td>
 <td><?php echo $obj['dob']; ?></td>
 <td><?php echo $obj['email']; ?></td>
 </tr>

 <?php
 $i++;
 }
 }
 else
 {
 ?>

 <tr>
 <td>No Data Available !! Please redifine your Search.... </td>
 </tr>

 <?php
 }
 ?>
 <tr>
 <td><?php echo "<hr>".$paging->print_link();?></td>
 </tr>

 </table>

Sending Mail

Sending mail using PHP is very simple. Here I’ll show how we can send the activation mail to a registered using along with the verification key we generated in last post.

<?php
    $emailto= "recipient@example.com";
    $frmname="yourid@yoursite.com";
    $subject	= "Activation-yoursite.com";
    $min_size	= "1";
    $max_size	= "4000";
    $headers  = "MIME-Version: 1.0\r\n";
    $headers .= "Content-type: text/html; charset=iso-8859-1\r\n";
    $headers .="To:".$emailto."<".$emailto.">\r\n";
    $headers .="From:".$frmname."<".$email.">\r\n";
    $headers 	= "From: yourid@yoursite.com";
    $message	= "Registration Successfull!!\n\nThank you for registering with us. \n\nUser name: ". $username . "\nPassword: ". $password ."\n\n Click here for activation.\n www.yoursite.com/activate.php?verikey=".$pass;
   $ok = @mail($emailto, $subject, $message, $headers);
   $msg	= "Registered Successfully";
   header("location:register_suc.php?msg=$msg");
?>

This will send the recipient with the username and password along with the verification key generated instructing them to click on the link to activate their profile. We will see how to implement the activation page in this post. We also need to understand how to first add the generated key to database.

Actually adding the generated key to database is as easy as any other PHP-MySQL queries. I’ll just give an example here.

$qry = "INSERT INTO users (name, password, email, vkey) VALUES ('$uname', '$passwd', '$email', '$pass');
mysql_query($qry);

We’ll be having a field in the ‘users‘ table named ‘status‘ which is by default ‘N’. The purpose of the activate page is set this to ‘Y‘. It is really very easy. Here is the code in the ‘activate.php‘ page.

$verikey = $_GET['verikey'];
 $qry = "UPDATE users SET status = 'Y' WHERE vkey = '$verikey'";
 mysql_query($qry);

Generate Verification Key

While registering with a website we often need to verfy our email id. Given below is the code to develop that functionality. The following will generate the verification key which has 6 characters

function generatePassword()
{
    $length =6;
    $validchars = "0123456789abcdfghjkmnpqrstvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";

    $password ="";
    $counter = 0;

    while($counter < $length)
    {
        $actChar = substr($validchars, rand(0, strlen($validchars)), 1);

        if(!strstr($password, $actchar))
       {
           $password .= $actChar;
           $counter++;
       }
   }

   return $password;
}

rand(0, stlen($validchars)) – generates a random number between 0 and the length of $validchars (inclusive of both ends).

substr($a, $b , len) – get generates a sub string from $a from the first occurrence of $b to length specified by len.

strstr($a, $b) – checks whether $a has $b in it. This is done to create unique characters.

So this is how you generate random string. How you can use it for verification purpose of a user registration is explained in the subsequent posts.

Basic connection string

This is very very novice kind of thing. Every web application requires script like this. Usually we write the following in a file named connection.inc which would later be included in files as needed.

$host = "localhost";
$dbname = "database_name";
$username = "user";
$password = "pass";

function dbConnect()
{
    global $host, $username, $password, $dbname;
    mysql_pconnect($host, $username, $password) or die("Error connecting to database");
    mysql_select_db($dbname) or die("Cannot select the database");
}

mysql_pconnect() makes a persistent connection. When connection it listens for any open connections and uses it if available. Also once the script ends it won’t close the connection. It will remain open for any further connections. It cannot also not closed with mysql_close() function.

What the Llama taught me? Part – 1

Yesterday I finished reading the Llama book. I need to go through the book again since I didn’t get a thorough understanding of all the contents especially the last chapters. Any how I got a glimpse of what Perl could do and I’m so amazed by most of what it could do, that I ordered 4 books of the Internet, the Llama, Alpace, Vicuna and Camel (The Llama I hold now is a friend’s copy).

Here are some of the new constructs I learned in Perl and some others which are there in other languages but treated differently in Perl. (NB: I have only recently started learning Perl and my experience is litle. So these are what I understood, may be some are not perfectly right. But If some one points out so, I’m willing to correct my entry.)

I believe a newbie can read this and get a bird’s eye view of Perl before getting hold of a Llama.

1) There are no integers. All numerals are treated like floating point by Perl. So 10/3 yields 3.3333… always. However in the case of ‘%’ floats are converted to integers (I’m not sure how Perl makes this possible as there isn’t an integer in Perl, or so I’m said, Some one may give an explanation in comments.).

2) Underscores can be used to add clarity to integer literals.
eg : 12_345_678 is equal to 12345678

3) Principle of “no built-in limits“. eg: You string length can range from 0 to infinity(meaning how much your memory can hold).

4) String repetition operator ‘x’.
eg: "Chris" x 3 is ChrisChrisChris.
Once again here too, if the right operator is a float it is truncated to corresponding integer value.

5) The block curly braces are ALWAYS needed around the conditional code. This is some kind of an inconvenience compared to C rule of no need for the braces if condition is followed by a single line. I believe this is made compulsory to aid readability.

6) The use of an uninitialized variable doesn’t yield a fatal error. Uninitialized variables are pre initialized with a special value ‘undef’, which acts like ‘0’ in numeric context and as empty string in string context. Using the ‘warnings’ pragma will sometimes arise a warning about the use of ‘undef’ values’. There is a defined() function to check whether a variable is defined.

7) There is no need to declare the aray size. It can grow up to whatever size it like. If you declare $fred[999] = 'somevalue' for an array @fred which earlier had only 2 members, the above code would extend the array to 1000 elements with all the elements from $fred[2] to $fred[998] as ‘undef’.
Also you can index the array with a float number(It isn’t an error, but will be truncated) so $fred[2.324] means $fred[2]. You can even use the above said technique of ‘underscores’ to denote an array inex. eg $fred[123_456]
The last array index can be found out by $#fred. Also you can use negative array index to access the array from end. eg $fred[-1] is equal to $fred[$#fred].

8 ) The list literals are  great innovation. The range operator (..) and qw shortcut are great way to ease the coding. [NB: The range operator only counts uphill , there is a reverse function for the opposite.]
The list assignments is an easy way to assign values.

9) The list construct makes it easy to swap two variables easily, that too without a third variable.
eg: ($fred, $barney) = ($barney, $fred) # This swaps the contents of the two variables.
Wow! What an idea!. That’s why I said list is indeed an innovation. There are more techniques like these in lists. When working with lists you will feel that Perl has got artificial intelligence of some sort. It knows to discard values when the two sides of the equal signs aren’t balanced.(Actually as a matter of fact, there are a lot of places where we feel Perl has got AI built in. May be it’s the reason why people complain Perl is hard. Here we are dealing with a beast which has got brains of it’s own. So it’s quite natural to need brains to tame it)

10) push, pop, shift, unshift etc are some array operators which makes life easy while working with arrays.

11) Once again a portion, where Perl shows intelligence. It knows whether you are talking in scalar or list context. So we also need to be intelligent enough to know the context while talking with Perl.
eg : reverse in list context gives the list from the last member whereas n string context reverses the string. You can force a list to scalar context by explicitly using the scalar keyword.

12) Sub routines in Perl is a section where there is a lot of astonishments in store for a newbie. The usual method of calling a subroutine is &<sub routine name>, but it is not always so. If Perl can understand it is a function call somehow then you can use a simple <sub routine name>. This means if the sub routine definition is provided in the code before the call or if there are parameters in the function call(If there are parameters, it ought to be a function, cool logic. isn’t it.?). Now even the skeptics among you can believe my claim ‘Perl is intelligent’.

13) There may or may not be return in a function. If there isn’t a return, the result of the last executed line of code is the return value (Please make sure you understand correctly what is returned since in the earlier days of Perl this can rise a lot of troubles)

14) There are multitude of default variables like $/, $_ etc which maybe confusing at first but once start to get going, these makes life more easy. for eg: $_ default variable makes it possible to write the foreach loop like
foreach (1..10) {
print($_);
}

instead of
foreach $num (1..10) {
print($num);
}

both of the print the numbers from 1 to 10, but the former one may be easier to write. You may decide which one you should use. If you find the second one more readable or say more in tandem with your foreach constructs in other languages go for the second.

15) I have been saying this for a while but even the motto for Perl is ‘There is more than one way to do it’. Do you know we can even write the for instead of the foreach in the above example.

There is more I can say, but I read somewhere the attention span of the average reader diminish by 70% after the first 15 points , so I’m reserving the rest of it for another post.

So here is what to emphasize before the small break.

So Perl is an intelligent beast which is wild(read as powerful) but yet domesticable(suits even the beginner) [Can you find a similarity with camel?]. If you are in any doubt, please try it, and be amazed.

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