Developing the Subscription Mechanism

You learned in earlier lessons that planning is the most important aspect of creating any product. In this case, think of the elements you will need for your subscription mechanism:

A table to hold email addresses
A way for users to add or remove their email addresses
A form and script for sending the message

The following sections will describe each item individually.

Creating the `subscribers` Table

You really need only one field in the subscribers table: to hold the email address of the user. However, you should have an ID field just for consistency among your tables, and also because referencing an ID is a lot simpler than referencing a long email address in where clauses. So, in this case, your MySQL query would look something like

 mysql> create table subscribers (     -> id int not null primary key auto_increment,     -> email varchar (150) unique not null     -> ); Query OK, 0 rows affected (0.00 sec)

Note the use of unique in the field definition for email. This means that although id is the primary key, duplicates should not be allowed in the email field either. The email field is a unique key, and id is the primary key.

 mysql> desc subscribers; +-------+--------------+------+-----+---------+----------------+ | Field | Type         | Null | Key | Default | Extra          | +-------+--------------+------+-----+---------+----------------+ | id    | int(11)      |      | PRI | NULL    | auto_increment | | email | varchar(150) |      | UNI |         |                | +-------+--------------+------+-----+---------+----------------+ 2 rows in set (0.00 sec)

Now that you have a table, you can create the form and script that place values in there.

Creating the Subscription Form

The subscription form will actually be an all-in-one form and script called manage.php, which will handle both subscribe and unsubscribe requests. Listing 18.1 shows the code for manage.php, which uses a few user-defined functions to eliminate repetitious code. The code looks long, but a line-by-line description follows, and the majority of the code is an HTML form, so no worries!

Listing 18.1. Subscribe and Unsubscribe with `manage.php`

  1: <?php  2: //set up a couple of functions  3: function doDB() {  4:     global $conn;  5:    //connect to server and select database; you may need it  6:    $conn = mysql_connect("localhost", "joeuser", "somepass")  7:         or die(mysql_error());  8:    mysql_select_db("testDB",$conn) or die(mysql_error());  9: } 10: 11: function emailChecker($email) { 12:     global $conn, $check_result; 13:    //check that email is not already in list 14:    $check = "select id from subscribers where email = '$email'"; 15:    $check_result = mysql_query($check,$conn) or die(mysql_error()); 16: } 17: 18: //determine if they need to see the form or not 19: if ($_POST[op] != "ds") { 20:    //they do, so create form block 21:    $display_block = " 22:    <form method=POST action=\"$_SERVER[PHP_SELF]\"> 23: 24:    <p><strong>Your E-Mail Address:</strong><br> 25:    <input type=text name=\"email\" size=40 maxlength=150> 26: 27:    <p><strong>Action:</strong><br> 28:    <input type=radio name=\"action\" value=\"sub\" checked> subscribe 29:    <input type=radio name=\"action\" value=\"unsub\"> unsubscribe 30: 31:    <input type=\"hidden\" name=\"op\" value=\"ds\"> 32: 33:    <p><input type=submit name=\"submit\" value=\"Submit Form\"></p> 34:    </form>"; 35: 36: } else if (($_POST[op] == "ds") && ($_POST[action] == "sub")) { 37:    //trying to subscribe; validate email address 38:    if ($_POST[email] == "") { 39:        header("Location: manage.php"); 40:        exit; 41:    } 42:    //connect to database 43:    doDB(); 44:    //check that email is in list 45:    emailChecker($_POST[email]); 46: 47:    //get number of results and do action 48:    if (mysql_num_rows($check_result) < 1) { 49:        //add record 50:        $sql = "insert into subscribers values('', '$_POST[email]')"; 51:        $result = mysql_query($sql,$conn) or die(mysql_error()); 52:        $display_block = "<P>Thanks for signing up!</P>"; 53:    } else { 54:        //print failure message 55:        $display_block = "<P>You're already subscribed!</P>"; 56:    } 57: } else if (($_POST[op] == "ds") && ($_POST[action] == "unsub")) { 58:    //trying to unsubscribe; validate email address 59:    if ($_POST[email] == "") { 60:        header("Location: manage.php"); 61:        exit; 62:    } 63:    //connect to database 64:    doDB(); 65:    //check that email is in list 66:    emailChecker($_POST[email]); 67: 68:    //get number of results and do action 69:    if (mysql_num_rows($check_result) < 1) { 70:        //print failure message 71:        $display_block = "<P>Couldn't find your address!</P> 72:        <P>No action was taken.</P>"; 73:    } else { 74:        //unsubscribe the address 75:        $id = mysql_result($check_result, 0, "id"); 76:        $sql = "delete from subscribers where id = '$id'"; 77:        $result = mysql_query($sql,$conn) or die(mysql_error()); 78:        $display_block = "<P>You're unsubscribed!</p>"; 79:    } 80: } 81: ?> 82: <HTML> 83: <HEAD> 84: <TITLE>Subscribe/Unsubscribe</TITLE> 85: </HEAD> 86: <BODY> 87: <h1>Subscribe/Unsubscribe</h1> 88: <?php echo "$display_block"; ?> 89: </BODY> 90: </HTML>

Listing 18.1 may be long, but it's not complicated. In fact, it could be longer, were it not for the user-defined functions at the top of the script. One of the reasons for creating your own functions is to be able to reuse it within your scripts. Lines 39 set up the first function, doDB(), which is simply the database connection you've been making in your lessons for a while now. Lines 1116 define a function called emailChecker(), which takes an input and returns an outputlike most functions do. We'll look at this one in the context of the script, as we get to it.

Line 19 starts the main logic of the script. Because this script performs several actions, we need to determine which action it is currently attempting. If the value of $_POST[op] is not "ds" (that stands for "do something"), we know the user has not submitted the form; therefore, we must show it to the user.

Lines 2134 create the subscribe/unsubscribe form, using $_SERVER[PHP_SELF] as the action (line 22), creating a text field called email for the user's email address, and setting up a set of radio buttons (lines 2829) to find the desired task. At this point, the script breaks out of the if...else construct, skips down to line 82, and proceeds to print the HTML. The form is displayed as shown in Figure 18.1.

Figure 18.1. The subscribe/unsubscribe form.

Back inside the if...else construct, if the value of $_POST[op] is indeed "ds", we need to do something. There are two possibilities: subscribing and unsubscribing. We determine which action to take by looking at the value of $_POST[action], from the radio button group.

In line 36, if the value of $_POST[op] is "ds" and the value of $_POST[action] is "sub", we know the user is trying to subscribe. To subscribe, he will need an email address, so we check for one in lines 3841. If no address is present, the user is redirected back to the form.

However, if an address is present, we call the doDB() function in line 43 to connect to the database, to issue a query (or two). In line 45, we call the second of our user-defined functions: emailChecker(). This function takes an input ($_POST[email], in this case) and processes it. If we look back to lines 1215, we see that the function is checking for an id value in the subscribers table, when the email address stored in the record that matches the value passed to the function. The function then returns the result set, called $check_result, for use within the larger script.

By the Way

Note the definition of global variables at the beginning of both user-defined functions in Listing 18.1. These variables need to be shared with the entire script, and so are declared global.

Jump down to line 48 to see how the $check_result variable is used: The number of records referred to by the $check_result variable is counted to determine whether the email address already exists in the table. If the number of rows is less than 1, the address is not in the list, and it can be added. The record is added and the response is stored in lines 5052, and the failure message (if the address is already in the table) is stored in line 55. At that point, the script breaks out of the if...else construct, skips down to line 82, and proceeds to print the HTML. You'll test this functionality later.

The last combination of inputs occurs if the value of the $_POST[op] variable is "ds" and the value of the $_POST[action] variable is "unsub". In this case, the user is trying to unsubscribe. To unsubscribe, he will need an email address, so we check for one in lines 5961. If no address is present, the user is sent back to the form.

If an address is present, we call the doDB() function in line 64 to connect to the database. Then, in line 66, we call emailChecker(), which again will return the result set, $check_result. The number of records in the result set is counted in line 69, to determine whether the email address already exists in the table. If the number of rows is less than 1, the address is not in the list, and it cannot be unsubscribed.

In this case, the response message is stored in lines 7172. The user is unsubscribed (the record deleted) and the response is stored in lines 7577, and the failure message (if the address is already in the table) is stored in line 78. At that point, the script breaks out of the if...else construct, skips down to line 82, and proceeds to print the HTML.

Figures 18.2 through 18.5 show the various results of the script, depending on the actions selected and the status of email addresses in the database.