2608-Forms.txt

Input Forms 
===================================================================

The <form> element
--------------------

    The <form> element is responsible to send data from client machine
    to server machine (or server program).

    There are two ways to send "user" input to the server.
  
        1. <form> tag

        2. JavaScript's XmlHttpRequest (XHR) (We'll discuss this 					     feature later)

    Basic syntax of <form> tag
    --------------------------
 
      <form method="post | get"
            action="server_program_name.php"
            id="form_id_for_javascript"
            name="form_name_for_javascript">

           <input ...../>
      </form>
 
      Any <input/> element placed inside the <form> must have "name"
      attribute. If "name" attribute is not set then "data" will not
      be sent.


      Method attribute - POST or GET
      ------------------------------
      There are two request types -- GET or POST. The default request
      type of any resource is "GET". When we request a page or resource
      from addressbar or clicking at link, it is "GET" request method.

      GET request send data into plain-text (human readable form) via
      addressbar.

          e.g

           http://localhost/sample.php?no=10&name=rajesh

          where ?no=10&name=rajesh is known as "Query String" where           each key(name)-value pair seperated by & sign.

     POST request send data into "encoded" or array of bytes to the      server and on server end they are decoded. You can use HTTPS -- HyperText Transfer Protocol Secured Socket Layer to encrypt/decrypt (CIpher) the data for better data security.

     When to use "GET" request type?
     ===============================

        1. Never use GET request when submitted data will be written
		disk file or database or they will be processed for any
		serious/important tasks.
        2. GET Request cannot handle huge amount of data. ie. data-		length is limit by the addressbar URL.
	3. GET request data can be easily tempered or altered.
        4. GET request cannot be used to upload files or send binary 		data.

      GET should be used when we need data for readonly purpose or we       dont want to pass data at all.

     When to use "POST" request type?
     ====================================

       1. Data to be stored into database/file or data are used to perform some important tasks like comparing username, password, email, credit card and so on.

       2. To upload a file

       3. To send huge amount of data. No limit on data length.


    Action attribute
    ======================================
              
        Send data will be received in a program file which is defined
	with action attribute. If action attribute is not given then
	the current web-page will receive the requested data.

   Id and name attribute
   =========================================
      
        Id and name attribute specifically used by JavaScript to
        select <form> DOM and perform DOM manipulation.

Example: GET Request
-----------------------------------------------

page_get.php
----------------

<form method="get" action="get_data.php">
  <br/>No: <input type="text" name="no"/>
                                ^
                                |------- Do not forget to set name
				|	 attribute
                                V
  <br/>Name:<input type="text" name="name"/>
  <br/><input type="submit" name="cmd" value="Submit"/>
</form>


When we press "Submit" button, the <form> will collect name-value pairs from <input/> elements and sent them to server. On server side program file "get_data.php" will receive these data using $_POST, $_GET or $_REQUEST superglobal arrays.

1. $_POST -- The POST request will populate $_POST array
2. $_GET  -- The GET request will populate $_GET array
3. $_REQUEST -- The GET or POST request will populate $_REQUEST array

These array are created by PHP environment and they are available to any PHP program, class, function and that's why they are called "Superglobals".

get_data.php
===========================
<?php
 
 $no = 0;
 $name = "";

 if(isset($_GET["no"], $_GET["name"])){
    $no = $_GET["no"];
   $name= $_GET["name"];
   echo $no, $name;
 }else{
   echo "Sorry! no data to proceed.";
 }
?>


POST request example:

page_post.php
----------------

<form method="post" action="post_data.php">
  <br/>No: <input type="text" name="no"/>
                                ^
                                |------- Do not forget to set name
				|	 attribute
                                V
  <br/>Name:<input type="text" name="name"/>
  <br/><input type="submit" name="cmd" value="Submit"/>
</form>

post_data.php
-------------------
<?php
 
 $no = 0;
 $name = "";

 if(isset($_POST["no"], $_POST["name"])){
    $no = $_POST["no"];
   $name= $_POST["name"];
   echo $no, $name;
 }else{
   echo "Sorry! no data to proceed.";
 }
?>


Example : Same page postback -- no action attribute is set.
------------------------------------------------------------------

In this example, same program is used to send and receive data.

same_post.php
--------------------------------

<?php

 /* create variables */ 
 $no = 0;
 $name = "";
 $cmd = "";
 $message = "";  // To display messages

 /* Examine the which button is pressed */
 
 if(isset($_POST["cmd"])){
    $cmd = $_POST["cmd"];
  }

 /* Add button specific code */ 
 if($cmd == "Add") {
   $no = 0 + $_POST["no"];
   $name = $_POST["name"];

   echo "<br/>", $no, $name;

  }
?>
<form method="post"> <!-- or set action="same-page.php" -->
 <br/>No : <input type="text" name="no"/>
 <br/>Name : <input type="text" name="name"/>
 <br/><input type="submit" name="cmd" value="Add"/>
</form>