Create Basic Databases and Integrate with a Website Lesson 5

Transcription

1 Create Basic Databases and Integrate with a Website Lesson 5 Forum Project In this lesson we will be creating a simple discussion forum which will be running from your domain. If you wish you can develop it on your local computer using phpdev, but the intention is for this project to be running live. We will need to create the database tables, user input forms, and display of the results. When broken into pieces like this, such a task seems quite simple as indeed it is! The ultimate goal is to understand the concepts and relationships that go into making something like a discussion forum, not to create the world s most fully-functional system. You will see it is quite sparse, but it is definitely relational. To make this project work you will need to: Create the forum posts and topics tables Create a front end for creating and reading posts Create the scripts that pull it together Plan Your System Once again, before you start with any database project you need to stop and think of the elements you will need for your system. You will need: 1. A table to hold the forum topics 2. A table to hold the actual forum postings 3. A way for users to add or read the topics Think about the basic components of a forum: topics and posts. A forum, if properly used, should have several topics, and each of these topics will have one or more posts submitted by users. Knowing that, you should realise that the posts are tied to the topics through a key field. This key forms the relationship between the two tables. Now what about the requirements for the topics themselves? You will definitely need a field for the title, and subsequently you may want fields to hold the creation time and the identification of the user who created the topic. Similarly, think of the requirements for the posts you ll want to store the text of the post, the time it was created, and the person creating it. Most importantly, you need the key to tie the post to the topic. Create the Forum Topics Table To create your table, you can either use a script, login to MySQL locally as we have in previous lessons, or use the phpmyadmin interface. Once again I recommend you try using the phpmyadmin interface by opening a browser window and typing the address db.username.cessnock-ict.net. As you only have one database on your domain, to hold all your tables, then we should prefix the table names in a way that indicates which project the tables belongs too. So rather than just using topics as a name we ll use forum_topics. The SQL code would be: CREATE TABLE forum_topics ( topic_id int not null primary key auto_increment, topic_title varchar (150), topic_create_time datetime, topic_owner varchar (150) ); Go ahead and create the table in your existing (default) database. 1

2 Create the Forum Posts Table We ll name our table to hold the posts as forum_posts. The SQL code would be: CREATE TABLE forum_posts ( post_id int not null primary key auto_increment, topic_id int not null, post_text text, post_create_time datetime, post_owner varchar (150) ); Go ahead and create the table in your existing database. You should now have 2 empty tables, which can form a relationship like that indicated in the image above. The tables are now waiting for some input. We ll create the input forms for adding a topic and a post, but first we should consider reusability and manageability issues Segregate Your Code At this stage all your samples, tutorial examples and challenge tasks etc., are all stored in a single directory (folder) on the server. As a means to create a tidier and more manageable file system, it would be desirable to have separate folders for each project. Using Dreamweaver or an FTP application, create a folder on your server called Forum in which to store the entire Forum Project. Create the Forum folder in the PHP directory that we have been using since the beginning of this series of tutorials. So, the full path to your Forum would be: Modularise Your Code When planning and designing a project, think about clumping related function together into a single php file that can be included recall we referred to this as a library file. One good example would be for handling the database connectivity issues. We could create a single file called dbstuff.php that contains the connectivity variables and functions we need. This means we won t need to repeat any of our code elsewhere. For example, to open a connection to the database we could have a single opendb() function call; to close our connection we could have a single closedb() function call. It makes the whole coding process much simpler and less error-prone. Create the file from the following code (or you could copy it from your previous Mailing List project). <?php //Global variable declaration $host = 'db.username.cessnock-ict.net'; $username = 'username'; $password = 'student1'; $db = 'usernamedb'; 2

3 // opendb function will create a connection to our MySQL server, then select the database function opendb() { global $conn, $host, $username, $password, $db; $conn = mysql_connect($host, $username, $password) or die(mysql_error()); mysql_select_db($db, $conn) or die(mysql_error()); // closedb function is used to formally close our MySQL database connection function closedb(){ global $conn; mysql_close($conn);?> Save the code as dbstuff.php in the Forum directory. Create the Input Forms and Scripts Before you can add any posts, you must add a topic to the forum. It is common practice in forum creation to add the topic and add the first post in that topic at the same time. From a user s point of view, it doesn t make much sense to add a topic, and then go back, select the topic and add a reply. You want the process to be as smooth as possible. Create the code below to present the form to the user. <html> <head> <title>add a Topic</title> </head> <body> <h1>add a Topic</h1> <form method=post action="addtopic.php"> <p><strong>your Address:</strong><br> <input type="text" name="topicowner" size=40 maxlength=150></p> <p><strong>topic Title:</strong><br> <input type="text" name="topictitle" size=40 maxlength=150></p> <p><strong>post Text:</strong><br> <textarea name="posttext" rows=8 cols=40 wrap=virtual></textarea></p> <p><input type="submit" name="submit" value="add Topic"></p> </form> </body> </html> Save the code above as addtopic.html in your Forum folder. 3

4 The form seems simple enough three fields are all you need to complete both tables as your script will complete the rest. Create the Add Topic and Post Script To create the entry in the forum_topics table, you use the values from the $_POST[topicTitle] and $_POST[topicOwner] variables from the input form. The topic_id will be automatically incremented and topic_create_time fields added via the now() MySQL function. Similarly in the forum_posts table, you use the values of $_POST[postText] and $_POST[topicOwner] from the input form. The post_id will be automatically incremented and the post_create_time added the same as above. Because you need a topic_id to be able to complete the post entry in the forum_post table, you know the query must happen after the query to insert the record in the forum_topics table. It would also seem reasonable that we check to make sure that all three fields have some content, before attempting to go any further. Let s now create the script that adds an entry to both forum_topics and forum_posts. <?php //check for required fields from the form if ((!$_POST[topicOwner]) (!$_POST[topicTitle]) (!$_POST[postText])) { header("location: addtopic.html"); exit; include("dbstuff.php"); //connect to server and select database opendb(); //create and issue the first query $add_topic = "INSERT INTO forum_topics VALUES ('', '$_POST[topicTitle]', now(), '$_POST[topicOwner]')"; mysql_query($add_topic,$conn) or die(mysql_error()); //get the id of the last query $topic_id = mysql_insert_id(); 4

5 //create and issue the second query $add_post = "INSERT INTO forum_posts VALUES ('', '$topic_id', '$_POST[postText]', now(), '$_POST[topicOwner]')"; mysql_query($add_post,$conn) or die(mysql_error()); //create nice message for user $topictitle = $_POST[topicTitle]; $display_block = "<P>The <strong>$topictitle</strong> topic has been created.</p>";?> <html> <head> <title>new Topic Added</title> </head> <body> <h1>new Topic Added</h1> <?php echo $display_block;?> </body> </html> Save the code above as addtopic.php in the Forum folder. Test the Add Topic Mechanism Load the addtopic.html file from your server and make an entry like this example After submitting the topic, you should be presented with the output 5

6 Picking it to pieces Looking at some of the relevant lines of code we have: if ((!$_POST[topicOwner]) (!$_POST[topicTitle]) (!$_POST[postText])) { header("location: addtopic.html"); exit; The first thing that happens is that there is a test to ensure that there is content in the submitted variables and that the submission was from a POST. If any details are missing, or the script was not accessed through a post, then the user is presented with the form to complete. include("dbstuff.php"); opendb(); Include that database stuff that is required to connect to MySQl, and then actually open the database. $add_topic = "INSERT INTO forum_topics VALUES ('', '$_POST[topicTitle]', now(), '$_POST[topicOwner]')"; mysql_query($add_topic,$conn) or die(mysql_error()); Create the query string and execute the query. If the query fails then an error message is generated and the program will crash out (die). //get the id of the last query $topic_id = mysql_insert_id(); Now this piece of code is new and is a clever way of finding a specific piece of information from the previously run query just above i.e. the inserting of the forum_topics record. The MySQL manual describes the mysql_insert_id() function this way: mysql_insert_id() Returns the value generated for an AUTO_INCREMENT column by the previous INSERT or UPDATE statement. Use this function after you have performed an INSERT statement into a table that contains an AUTO_INCREMENT field. More precisely, mysql_insert_id() is updated under these conditions: INSERT statements that store a value into an AUTO_INCREMENT column. This is true whether the value is automatically generated by storing the special values NULL or 0 into the column, or is an explicit non-special value. In the case of a multiple-row INSERT statement, mysql_insert_id() returns the first automatically generated AUTO_INCREMENT value; if no such value is generated, it returns the last last explicit value inserted into the AUTO_INCREMENT column. INSERT statements that generate an AUTO_INCREMENT value by inserting LAST_INSERT_ID(expr) into any column. INSERT statements that generate an AUTO_INCREMENT value by updating any column to LAST_INSERT_ID(expr). The value of mysql_insert_id() is not affected by statements such as SELECT that return a result set. If the previous statement returned an error, the value of mysql_insert_id() is undefined. Note that mysql_insert_id() returns 0 if the previous statement does not use an AUTO_INCREMENT value. If you need to save the value for later, be sure to call mysql_insert_id() immediately after the statement that generates the value. 6

7 The value of mysql_insert_id() is affected only by statements issued within the current client connection. It is not affected by statements issued by other clients. So in essence, you don t have to issue a SELECT MAX(topic_id) FROM forum_topics query just to find out what the topic_id value should be. What a useful trick this is $add_post = "INSERT INTO forum_posts VALUES ('', '$topic_id', '$_POST[postText]', now(), '$_POST[topicOwner]')"; mysql_query($add_post,$conn) or die(mysql_error()); Here we issue the second INSERT query string, using the topic_id and the now() function. The now() function is used essentially the same as you would in other applications like Microsoft Excel. The function returns the current date and time. This is also a handy way of not needing to be concerned with formatting the date or time to suit MySQL. Another function worthy of remembering! The rest of the code is straightforward. Displaying the Topic List Now that you have a topic and at least one post in your database, you can display this information and let people add new topics or reply to existing ones. But before we go any further we should create a script that displays a list of all the topics in the forum. This page will show the basic information of each topic and provide the user with a link to add a new topic. There should be nothing in the code that you wouldn t have seen before except for some date formatting. <?php // connect to server and select database include("dbstuff.php"); opendb(); // gather the topics from the forum_topics table $get_topics = "SELECT topic_id, topic_title, topic_owner, date_format(topic_create_time,'%b %e %Y at %r') AS creation_time FROM forum_topics ORDER BY creation_time desc"; $get_topics_result = mysql_query($get_topics, $conn) or die(mysql_error()); if (mysql_num_rows($get_topics_result) < 1) { //there are no topics $display_block = "<p><em>no topics exist.</em></p>"; else { //create the display string containing the topic info $display_block = "<table cellpadding=3 cellspacing=1 border=1> <tr> <th>topic TITLE</th> <th># of POSTS</th> </tr>"; while ($topic_info = mysql_fetch_array($get_topics_result)) { $topic_id = $topic_info['topic_id']; $topic_title = stripslashes($topic_info['topic_title']); $topic_create_time = $topic_info['creation_time']; $topic_owner = stripslashes($topic_info['topic_owner']); //get number of posts that have been submitted for the current topic $get_num_posts = "SELECT COUNT(post_id) AS num_posts FROM forum_posts WHERE topic_id = $topic_id"; $get_num_posts_result = mysql_query($get_num_posts,$conn) or die(mysql_error()); 7

8 $post_count_info = mysql_fetch_array($get_num_posts_result); $num_posts = $post_count_info['num_posts']; //add to display $display_block.= " <tr> <td><a href=\"showtopic.php?topic_id=$topic_id\"> <strong>$topic_title</strong></a><br> Created on $topic_create_time by $topic_owner</td> <td align=center>$num_posts</td> </tr>"; //close up the table $display_block.= "</table>";?> <html> <head> <title>topics in My Forum</title> </head> <body> <h1>topics in My Forum</h1> <?php echo $display_block;?> <p>would you like to <a href="addtopic.html">add a topic</a>?</p> </body> </html> Save the code as topiclist.php and test it out. If you have only added one post, then the display should be similar to the image below. Most of the code in topiclist.php is very straightforward, but there are a few lines that could be explained. date_format(topic_create_time,'%b %e %Y at %r') AS creation_time The MySQL date_format() function reference provides the following information. DATE_FORMAT(date, format) Formats the date value according to the format string. The following specifiers may be used in the format string: Specifier Description %a Abbreviated weekday name (Sun..Sat) %b Abbreviated month name (Jan..Dec) %c Month, numeric (0..12) 8

9 %D Day of the month with English suffix (0th, 1st, 2nd, 3rd,...) %d Day of the month, numeric (00..31) %e Day of the month, numeric (0..31) %f Microseconds ( ) %H Hour (00..23) %h Hour (01..12) %I Hour (01..12) %i Minutes, numeric (00..59) %j Day of year ( ) %k Hour (0..23) %l Hour (1..12) %M Month name (January..December) %m Month, numeric (00..12) %p AM or PM %r Time, 12-hour (hh:mm:ss followed by AM or PM) %S Seconds (00..59) %s Seconds (00..59) %T Time, 24-hour (hh:mm:ss) %U Week (00..53), where Sunday is the first day of the week %u Week (00..53), where Monday is the first day of the week %V Week (01..53), where Sunday is the first day of the week; used with %X %v Week (01..53), where Monday is the first day of the week; used with %x %W Weekday name (Sunday..Saturday) %w Day of the week (0=Sunday..6=Saturday) %X %x Year for the week where Sunday is the first day of the week, numeric, four digits; used with %V Year for the week, where Monday is the first day of the week, numeric, four digits; used with %v %Y Year, numeric, four digits %y Year, numeric (two digits) %% A literal % character All other characters are copied to the result without interpretation. Note that the % character is required before format specifier characters. Ranges for the month and day specifiers begin with zero due to the fact that MySQL allows the storing of incomplete dates such as ' '. Examples: SQL string: SELECT DATE_FORMAT(' :23:00', '%W %M %Y'); Output or Results: 'Saturday October 1997' SQL string: SELECT DATE_FORMAT(' :23:00', '%H:%i:%s'); Output or Results: '22:23:00' SQL string: SELECT DATE_FORMAT(' :23:00', 9

10 '%D %y %a %d %m %b %j'); Output or Results: '4th 97 Sat Oct 277' SQL string: SELECT DATE_FORMAT(' ', '%X %V'); Output or Results: ' ' So picking it to pieces we have a date provided with a format string of: '%b %e %Y at %r' which produces the output string: Oct at 01:15:18 AM Displaying the Posts in a Topic The next logical step is to be able to display the actual posts that have been submitted for each topic. The line of code that will trigger this action was <a href=\"showtopic.php?topic_id=$topic_id\"> which uses a link (so it will be a GET type of request) calling the showtopic.php script and passing the topic_id as part of the query string. The whole process hangs on getting the topic_id, as that is the foreign key in the forum_posts table, relating to the forum_topics. So it would be appropriate validation to first check that a valid topic_id has been passed to our showtopic.php script. If this script makes it past this point then we would extract the topic_title, then all the posts. Create the code below. <?php // check for required info from the query string if (!$_GET[topic_id]) { header("location: topiclist.php"); exit; // create the database connection include("dbstuff.php"); opendb(); // verify the topic exists $get_topic_query = "SELECT topic_title FROM forum_topics WHERE topic_id = $_GET[topic_id]"; $get_topic_result = mysql_query($get_topic_query, $conn) or die(mysql_error()); // there should be at least 1 topic_title in our database, if not then there is an error if (mysql_num_rows($get_topic_result) < 1) { // this topic does not exist - generate a suitable error message $display_block = "<p><em>you have selected an invalid topic. Please <a href=\"topiclist.php\">try again</a>.</em></p>"; else { // get the topic title from the query taking only the first row $topic_title = stripslashes(mysql_result($get_topic_result, 0, 'topic_title')); // get all the posts for this topic $get_posts_query = "SELECT post_id, post_text, post_owner, date_format(post_create_time, '%b %e %Y at %r') AS creation_time FROM forum_posts WHERE topic_id = $_GET[topic_id] ORDER BY post_create_time ASC"; 10

11 $get_posts_results = mysql_query($get_posts_query,$conn) or die(mysql_error()); // create the display string $display_block = " <p>showing posts for the <strong>$topic_title</strong> topic:</p> <table width=100% cellpadding=3 cellspacing=1 border=1> <tr> <th>author</th> <th>post</th> </tr>"; // for each posting, create a table row and included the contents of the post while ($posts_info = mysql_fetch_array($get_posts_results)) { $post_id = $posts_info['post_id']; $post_text = nl2br(stripslashes($posts_info['post_text'])); $post_create_time = $posts_info['creation_time']; $post_owner = stripslashes($posts_info['post_owner']); //add to display $display_block.= " <tr> <td width=35% valign=top>$post_owner<br>[$post_create_time]</td> <td width=65% valign=top>$post_text<br><br> <a href=\"replytopost.php?post_id=$post_id\"> <strong>reply TO POST</strong> </a></td> </tr>"; //close up the table $display_block.= "</table>";?> <html> <head> <title>posts in Topic</title> </head> <body> <h1>posts in Topic</h1> <?php echo $display_block;?> </body> </html> Save the code above as showtopic.php and test it. The output from the first post would look similar to this: 11

12 If there are more postings then, they should also be listed. Picking it to Pieces Most of the code above should look familiar except for a couple of new functions. $topic_title = stripslashes( mysql_result($get_topic_result, 0, 'topic_title') ); Here is a slightly different method of extracting a record (array) from the results returned from executing a MySQL query. Till now the method I have been using is to extract a single row from the results, then each part or field of the row (remember the row is an array in itself). The command we have been using is mysql_fetch_array(). Now it is possible (though unlikely) that when executing the mysql query to get the topic_title that more than a single row might be returned. To make the extraction of the topic_title field from the first record (row) only, we can be specific. Using the mysql_result( ) function you can extract a specific piece of information, provided you know exactly where to locate it, with less code. Less code means less typing When you have multiple records returned as part of a query you essentially have a two-dimensional array. An individual record is an array, where the fields can be accessed via a subscript (index) or by name (associative array). For instance we could use $post_info[0] or $post_info[ post_id ]. When we issue the function call mysql_fetch_array() we get one single record. But the overall results are stored as an array of records, or basically an array of arrays. The easiest way to visualise it is to think of a spreadsheet with each record having a row number except the rows start counting from zero. $post_text = nl2br(stripslashes($posts_info['post_text'])); The nl2br( ) function is a handy way of inserting HTML breaks before any new line characters found in the string. Adding Posts to a Topic The only step missing in our forum is the ability to reply to a post. After all how can you get a good argument going if only one person has a say The script will be called replytopost.php and doesn t hold any real secrets or difficulties. Well no more than has been thrown at you so far at least Well actually there might be something of interest. Create the code below <?php // add the database connection ability include("dbstuff.php"); // check to see if we're showing the form or adding the post if ($_POST[op]!= "addpost") { // showing the form, but now check for required item in query string if (!$_GET[post_id]) { header("location: topiclist.php"); exit; $verify_query = "SELECT forum_topics.topic_id, forum_topics.topic_title FROM forum_topics, forum_posts WHERE forum_posts.topic_id = forum_topics.topic_id AND forum_posts.post_id = $_GET[post_id]"; // create the database connection opendb(); 12

13 $verify_result = mysql_query($verify_query, $conn) or die(mysql_error()); if (mysql_num_rows($verify_result) < 1) { // this post or topic does not exist header("location: topiclist.php"); exit; else { // get the topic id and title $topic_id = mysql_result($verify_result,0,'topic_id'); $topic_title = stripslashes(mysql_result($verify_result, 0,'topic_title')); echo " <html><head> <title>post Your Reply in $topic_title</title> </head> <body> <h1>post Your Reply in $topic_title</h1> <form method=post action=\"$_server[php_self]\"> <p><strong>your Address:</strong><br> <input type=\"text\" name=\"post_owner\" size=40 maxlength=150> <p><strong>post Text:</strong><br> <textarea name=\"post_text\" rows=8 cols=40 wrap=virtual></textarea> <input type=\"hidden\" name=\"op\" value=\"addpost\"> <input type=\"hidden\" name=\"topic_id\" value=\"$topic_id\"> <p><input type=\"submit\" name=\"submit\" value=\"add Post\"></p> </form> </body> </html>"; else if ($_POST[op] == "addpost") { //check for required items from the form if ((!$_POST[topic_id]) (!$_POST[post_text]) (!$_POST[post_owner])) { header("location: topiclist.php"); exit; // create the database connection and add the new posting opendb(); $posttext = addslashes($_post[post_text]); $add_post = "INSERT INTO forum_posts VALUES ('', '$_POST[topic_id]', '$posttext', now(), '$_POST[post_owner]')"; mysql_query($add_post, $conn) or die(mysql_error()); closedb();?> //redirect user to topic header("location: showtopic.php?topic_id=$topic_id"); exit; Save the code above as replytopost.php and test it out. An example reply might look similar to the one below. 13

14 After adding the post above you should be returned to the list of posts for the current topic. The Query String in Different Ways Our forum database has two tables which can be related through the topic_id field. The query string that we used in the replytopost.php script, could be considered as not the done way for a proper relational query. The Query we used was: SELECT forum_topics.topic_id, forum_topics.topic_title FROM forum_topics, forum_posts WHERE forum_posts.topic_id = forum_topics.topic_id AND forum_posts.post_id = $_GET[post_id] However, if we were to write the statement using more precise relational techniques, the query might be written: SELECT ft.topic_id, ft.topic_title FROM forum_posts AS fp LEFT JOIN forum_topics AS ft ON fp.topic_id = ft.topic_id WHERE fp.post_id = $_GET[post_id]"; A LEFT JOIN is where all the entries for the table on the left are shown (so all the forum_posts will be in the query) and only those entries in the right table (forum_topics) are shown. The first example is the same as using an INNER JOIN. The important point I would put forward is as long as you get the correct results, that s all that matters (conditional: limited to this set of learning outcomes). You should be able to replace the first SELECT statement with the second and still obtain the same results. 14

15 Exercises Challenge 1 15