Phát triển web với PHP và MySQL - p 75 docx

FIGURE 29.2 There are three main parts of the blah-blah forum system. A summary of the files in this application is shown in Table 29.1. TABLE 29.1 Files in the Web Forum Application Name Type Description index.php Application The main page users will see when they enter the site. Contains an expandable and collapsible list of all the articles on the site. new_post.php Application Form used for posting new articles. store_new_post.php Application Stores articles entered in the new_post.php form. view_post.php Application Displays an individual post and a list of the replies to that post. treenode_class.php Library Contains the treenode class, which we will use to display the hierarchy of posts. include_fns.php Library Brings all the other function libraries for this application together (the other Library-type files listed here). data_valid_fns.php Library Data validation functions. db_fns.php Library Database connectivity functions. discussion_fns.php Library Functions for dealing with storing and retrieving postings. output_fns.php Library Functions for outputing HTML. create_database.sql SQL SQL to set up the database required for this application. Let’s go ahead and look at the implementation. Building Web Forums C HAPTER 29 29 BUILDING WEB FORUMS 715 Add a new articleView an article Article list (different views) reply 35 7842 CH29 3/6/01 3:34 PM Page 715 Designing the Database There are a few attributes we’ll need to store about each article posted to the forum: the person who wrote it, called the poster; the title of the article; when it was posted; and the article body. We will therefore need a table of articles. We’ll create a unique ID for each article, called the postid. Each article needs to have some information about where it belongs in the hierarchy. We could store information about an article’s children with the article. However, each article can have many replies, so this can lead to some problems in database construction. As each article can only be a reply to one other, it is easier to store a reference to the parent article, that is, the arti- cle that this article is replying to. That gives us the following data to store for each article: • postid: A unique ID for each article • parent: The postid of the parent article • poster: The author of this article • title: The title of this article • posted: The date and time that the article was posted • message: The body of the article We will add a couple of optimizations to this. When we are trying to determine whether an article has any replies, we will have to run a query to see whether any other articles have this article as a parent. We will need this information for every post that we list. The fewer queries we have to run, the faster our code will run. We can remove the need for these queries by adding a field to show whether there are any replies. We will call this field children and make it effectively Boolean—the value will be 1 if the node has children, and 0 if it does not. There is always a price to pay for optimizations. Here we are choosing to store redundant data. As we are storing the data in two ways, we must be careful to make sure that the two represen- tations agree with each other. When we add children, we must update the parent. If we allow the deletion of children, we need to update the parent node to make sure the database is consis- tent. In this project we are not going to build a facility for deleting articles, so we will avoid half of this problem. If you decide to extend this code, bear this issue in mind. It is worth noting that some databases would help us out a little more here. If we were using Oracle, it could maintain relational integrity for us. Using MySQL, which does not support triggers or foreign key constraints, we need to write our own checks and balances to make sure that data still makes sense each time we add or delete a record. Building Practical PHP and MySQL Projects P ART V 716 35 7842 CH29 3/6/01 3:34 PM Page 716 We will make one other optimization: We will separate the message bodies from the other data and store them in a separate table. The reason for this is that this attribute will have the MySQL type text. Having this type in a table can slow down queries on that table. Because we will do many small queries to build the tree structure, this would slow it down quite a lot. With the mes- sage bodies in a separate table, we can just retrieve them when a user wants to look at a particu- lar message. MySQL can search fixed size records faster than variable sized records. If we need to use vari- able sized data, we can help by creating indexes on the fields that will be used to search the database. For some projects, we would be best served by leaving the text field in the same record as everything else and specifying indexes on all the columns that we will search on. Indexes take time to generate though, and the data in our forums is likely to be changing all the time, so we would need to regenerate our indexes frequently. We will also add an area attribute in case we later decide to implement multiple chats with the one application. We won’t implement this here, but this way it is reserved for future use. Given all these considerations, the SQL to create the database for the forum database is shown in Listing 29.1. LISTING 29.1 create_database.sql—SQL to Create the Discussion Database create database discussion; use discussion; create table header ( parent int not null, poster char(20) not null, title char(20) not null, children int default 0 not null, area int default 1 not null, posted datetime not null, postid int unsigned not null auto_increment primary key ); create table body ( postid int unsigned not null primary key, message text ); Building Web Forums C HAPTER 29 29 BUILDING WEB FORUMS 717 35 7842 CH29 3/6/01 3:34 PM Page 717 grant select, insert, update, delete on discussion.* to discussion@localhost identified by ‘password’; You can create this database structure by running this script through MySQL as follows: mysql -u root -p < create_database.sql You will need to supply your root password. You should probably also change the password we have set up for the discussion user to something better. To understand how this structure will hold articles and their relationship to each other, look at Figure 29.3. Building Practical PHP and MySQL Projects P ART V 718 LISTING 29.1 Continued postid: 3 postid: 4 postid: 5 postid: 1 postid: 1 postid: 0 postid: 2 postid: 1 postid: 3 postid: 1 postid: 4 postid: 2 postid: 5 postid: 2 postid: 2 Database representation Tree representation FIGURE 29.3 The database holds the tree structure in a flattened relational form. As you can see, the parent field for each article in the database holds the postid of the article above it in the tree. The parent article is the article that is being replied to. You can also see that the root node, postid 1, has no parent. All new topics of discussion will be in this position. For articles of this type, we store their parent as a 0 (zero) in the database. Viewing the Tree of Articles Next, we need a way of getting information out of the database and representing it back in the tree structure. We will do this with the main page, index.php. For the purposes of this explana- tion, we have input some sample posts via the article posting scripts new_post.php and store_new_post.php. We will look at these in the next section. We will cover the article list first because it is the backbone of the site. After this, everything else will be easy. 35 7842 CH29 3/6/01 3:34 PM Page 718 Building Web Forums C HAPTER 29 29 BUILDING WEB FORUMS 719 FIGURE 29.4 The initial view of the article list shows the articles in “collapsed” form. What we see here are all the initiating articles. None of these are replies; they are all the first article on a particular topic. You will see that we have a number of options. There is a menu bar that will let us add a new post and expand or collapse the view that we have of the articles. To understand what this means, look at the posts. Some of them have plus symbols next to them. This means that these articles have been replied to. To see the replies to a particular article, you can click the plus symbol. The result of clicking one of these symbols is shown in Figure 29.5. As you can see, clicking the plus symbol has displayed the replies to that first article. The plus symbol has now turned to a minus symbol. If we click this, all the articles in this thread will be collapsed, returning us to the initial view. You might also notice that one of the replies has a plus symbol next to it. This means that there are replies to this reply. This can continue to an arbitrary depth, and you can view each reply set by clicking on the appropriate plus symbol. The two menu bar options, Expand and Collapse, will expand all possible threads and collapse all possible threads, respectively. The result of clicking the Expand button is shown in Figure 29.6. Figure 29.4 shows the initial view of the articles in the site that a user would see. 35 7842 CH29 3/6/01 3:34 PM Page 719 FIGURE 29.5 The thread of discussion about persistence has been expanded. Building Practical PHP and MySQL Projects P ART V 720 FIGURE 29.6 All the threads have now been expanded. 35 7842 CH29 3/6/01 3:34 PM Page 720 If you look closely at Figures 29.5 and 29.6, you can see that we are passing some parameters back to index.php in the command line. In Figure 29.5, the URL looks as follows: http://webserver/chapter29/index.php?expand=6#6 The script reads this as “Expand the item with postid 6”. The # is just an HTML anchor that will scroll the page down to the part that has just been expanded. In the second figure, the URL reads http://webserver/chapter29/index.php?expand=all Clicking the Expand button has passed the parameter expand with the value all. Expanding and Collapsing Let’s see how it’s done by looking at the index.php script, shown in Listing 29.2. L ISTING 29.2 index.php—Script to Create the Article View on the Main Page of the Application <? include (‘include_fns.php’); session_start(); // check if we have created our session variable if(!session_is_registered(‘expanded’)) { $expanded = array(); session_register(‘expanded’); } // check if an expand button was pressed // expand might equal ‘all’ or a postid or not be set if($expand) { if($expand == ‘all’) expand_all($expanded); else $expanded[$expand] = true; } // check if a collapse button was pressed // collapse might equal all or a postid or not be set if($collapse) { if($collapse==”all”) Building Web Forums C HAPTER 29 29 BUILDING WEB FORUMS 721 35 7842 CH29 3/6/01 3:34 PM Page 721 unset($expanded); else unset($expanded[$collapse]); } do_html_header(“Discussion Posts”); display_index_toolbar(); // display the tree view of conversations display_tree($expanded); do_html_footer(); ?> This script uses three variables to do its job. They are • The session variable $expanded, which keeps track of which threads are expanded. This can be maintained from view to view, so we can have multiple threads expanded. This variable is an associative array that contains the postid of articles which will have their replies displayed expanded. • The parameter $expand, which tells the script which new threads to expand. • The parameter $collapse, which tells the script which threads to collapse. When we click a plus or minus symbol or the Expand or Collapse button, they will re-call the index.php script with new parameters for $expand or $collapse. We use $expanded from page to page to track which threads should be expanded in any given view. The script begins by starting a session and adding the $expanded variable as a session variable if this has not already been done. After that, the script checks whether it has been passed an $expand or $collapse parameter and modifies the $expanded array accordingly. Look at the code for the $expand parameter: if($expand) { if($expand == ‘all’) expand_all($expanded); else $expanded[$expand] = true; } If we have clicked on the Expand button, the function expand_all() is called to add all the threads that have replies into the $expanded array. (We’ll look at this in a moment.) Building Practical PHP and MySQL Projects P ART V 722 LISTING 29.2 Continued 35 7842 CH29 3/6/01 3:34 PM Page 722 If we are trying to expand a particular thread, we will have been passed a postid via $expand. We therefore add a new entry to the $expanded array to reflect this. The expand_all() function is shown in Listing 29.3. LISTING 29.3 expand_all() Function from discussion_fns.php— Processes the $expanded Array to Expand All the Threads in the Forum function expand_all(&$expanded) { // mark all threads with children as to be shown expanded $conn = db_connect(); $query = “select postid from header where children = 1”; $result = mysql_query($query); $num = mysql_numrows($result); for($i = 0; $i<$num; $i++) { $expanded[mysql_result($result, $i, 0)]=true; } } This function runs a database query to work out which of the threads in the forum have replies, as follows: select postid from header where children = 1 Each of the articles returned is then added to the $expanded array. We run this query to save time later. We could simply add all articles to the expanded list, but it would be wasteful to try processing replies that do not exist. Collapsing the articles works in a similar but opposite way, as follows: if($collapse) { if($collapse==”all”) unset($expanded); else unset($expanded[$collapse]); } You can remove items from the $expanded array by unsetting them. We remove the thread that is to be collapsed, or unset the entire array if the entire page is to be collapsed. All this is preprocessing, so we know which articles should be displayed and which should not. The key part of the script is the call to display_tree($expanded); which will actually generate the tree of displayed articles. Building Web Forums C HAPTER 29 29 BUILDING WEB FORUMS 723 35 7842 CH29 3/6/01 3:34 PM Page 723 Displaying the Articles Let’s look at the display_tree() function, shown in Listing 29.4. LISTING 29.4 display_tree() Function from output_fns.php—Creates the Root Node of the Tree Structure function display_tree($expanded, $row = 0, $start = 0) { // display the tree view of conversations global $table_width; echo “<table width = $table_width>”; // see if we are displaying the whole list or a sublist if($start>0) $sublist = true; else $sublist = false; // construct tree structure to represent conversation summary $tree = new treenode($start, ‘’, ‘’, ‘’, 1, true, -1, $expanded, $sublist); // tell tree to display itself $tree->display($row, $sublist); echo “</table>”; } The main role of this function is to create the root node of the tree structure. We use it both to display the whole index and to create subtrees of replies on the view_post.php page. As you can see, it takes three parameters. The first, $expanded, is the list of article postids to display in an expanded fashion. The second, $row, is an indicator of the row number which will be used to work out the alternating colors of the rows in the list. The third parameter, $start, tells the function where to start displaying articles. This is the postid of the root node for the tree to be created and displayed. If we are displaying the whole thing, as we are on the main page, this will be 0 (zero), meaning display all the articles with no parent. If this parameter is 0, we set $sublist to false and display the whole tree. If the parameter is greater than 0, we use it as the root node of the tree to display, set $sublist to true and build and display only part of the tree. (We will use this in the view_post.php script.) The most important thing this function does is instantiate an instance of the treenode class that represents the root of the tree. This is not actually an article but it acts as the parent of all Building Practical PHP and MySQL Projects P ART V 724 35 7842 CH29 3/6/01 3:34 PM Page 724 . articles. store_new_post .php Application Stores articles entered in the new_post .php form. view_post .php Application Displays an individual post and a list of the replies to that post. treenode_class .php Library. relationship to each other, look at Figure 29.3. Building Practical PHP and MySQL Projects P ART V 718 LISTING 29.1 Continued postid: 3 postid: 4 postid: 5 postid: 1 postid: 1 postid: 0 postid: 2 postid:. main parts of the blah-blah forum system. A summary of the files in this application is shown in Table 29.1. TABLE 29.1 Files in the Web Forum Application Name Type Description index .php Application