Proxy and exception customization in PHP object-oriented programming (1)_PHP tutorial

1. DBQuery object

Now, our DBQuery object simply imitates a stored procedure—once executed, it returns a result resource that must be saved; and If you want to use functions on this result set (such as num_rows() or fetch_row()), you must pass a MySqlDB object. So, what is the effect if the DBQuery object implements the functions implemented by the MySqlDB object (which is designed to operate on the results of an executed query)? Let's continue using the code from the previous example; and let's assume that our result resources are now managed by a DBQuery object. The source code of the DBQuery class is shown in Listing 1.

Listing 1. Using the DBQuery class.

<ol class="dp-c">
<li class="alt"><span><span class="keyword">require</span><span> </span><span class="string">'mysql_db.php'</span><span>;   </span></span></li>
<li>
<span class="keyword">require_once</span><span> </span><span class="string">'query.php'</span><span>;   </span>
</li>
<li class="alt">
<span class="vars">$db</span><span> = </span><span class="keyword">new</span><span> MySqlDb;   </span>
</li>
<li>
<span class="vars">$db</span><span>->connect(</span><span class="string">'host'</span><span>， </span><span class="string">'username'</span><span>， </span><span class="string">'pass'</span><span>);   </span>
</li>
<li class="alt">
<span class="vars">$db</span><span>->query(</span><span class="string">'use content_management_system'</span><span>);   </span>
</li>
<li>
<span class="vars">$query</span><span> = </span><span class="keyword">new</span><span> DBQuery(</span><span class="vars">$db</span><span>);   </span>
</li>
<li class="alt">
<span class="vars">$query</span><span>->prepare(</span><span class="string">'SELECT fname，sname FROM users WHERE username=:1S AND pword=:2S AND expire_time<:3i><span>);   </span><li><span>try {   </span></li>
<li class="alt">
<span>　</span><span class="keyword">if</span><span>(</span><span class="vars">$query</span><span>->execute(</span><span class="string">"visualad"</span><span>， </span><span class="string">"apron"</span><span>， time()))->num_rows() == 1) {   </span>
</li>
<li>
<span></span><span class="func">echo</span><span>(</span><span class="string">'Correct Credentials'</span><span>);   </span>
</li>
<li class="alt">
<span>　} </span><span class="keyword">else</span><span> {   </span>
</li>
<li>
<span></span><span class="func">echo</span><span>(</span><span class="string">'Incorrect Credentials / Session Expired'</span><span>);   </span>
</li>
<li class="alt"><span>　}   </span></li>
<li>
<span>} catch (QueryException </span><span class="vars">$e</span><span>) {   </span>
</li>
<li class="alt">
<span>　</span><span class="func">echo</span><span>(</span><span class="string">'Error executing query: '</span><span> . </span><span class="vars">$e</span><span>);   </span>
</li>
<li><span>}   </span></li></:3i></span>
</li>
</ol>

What we are most interested in in the modified code above are the catch statement and execute statement.

◆The execute statement no longer returns a result resource, now it returns the DBQuery object itself.

◆The DBQuery object now implements the num_rows() function - which we are already familiar with from the DB interface.

◆If the query execution fails, it throws an exception of type QueryException. When converted to a string, it returns the details of the error that occurred.

For this, you need to use a PHP proxy. In fact, you are already using proxies in our DBQuery object, but now you will use it in more depth to tightly bind it to the MySqlDB object. The DBQuery object has been initialized with an object that implements the DB interface, and it already contains a member function execute—which calls the query() method of the DB object to execute the query. The DBQuery object itself does not actually query the database, it leaves this task to the DB object. This is a proxy, which is a process by which an object can implement a specific behavior by sending messages to another object that implements the same or similar behavior.

To do this, you need to modify the DBQuery object to include all the functions that operate on a result resource from the DB object. You need to use the stored results when executing a query to call the corresponding function of the DB object and return its results. The following functions will be added:

Listing 2: Extending the DBQuery class using proxies.

<ol class="dp-c">
<li class="alt"><span><span class="keyword">class</span><span> DBQuery   </span></span></li>
<li><span>{   </span></li>
<li class="alt"><span>　.....   </span></li>
<li><span> </span></li>
<li class="alt">
<span>　</span><span class="keyword">public</span><span> </span><span class="keyword">function</span><span> fetch_array()   </span>
</li>
<li><span>　{ 　  </span></li>
<li class="alt">
<span></span><span class="keyword">if</span><span> (! </span><span class="func">is_resource</span><span>(</span><span class="vars">$this</span><span>->result)) {   </span>
</li>
<li>
<span>　</span><span class="keyword">throw</span><span> </span><span class="keyword">new</span><span> Exception(</span><span class="string">'Query not executed.'</span><span>);   </span>
</li>
<li class="alt"><span>}   </span></li>
<li><span> </span></li>
<li class="alt">
<span></span><span class="keyword">return</span><span> </span><span class="vars">$this</span><span>->db->fetch_array(</span><span class="vars">$this</span><span>->result);   </span>
</li>
<li><span>　}   </span></li>
<li class="alt"><span> </span></li>
<li>
<span>　</span><span class="keyword">public</span><span> </span><span class="keyword">function</span><span> fetch_row()   </span>
</li>
<li class="alt"><span>　{   </span></li>
<li>
<span></span><span class="keyword">if</span><span> (! </span><span class="func">is_resource</span><span>(</span><span class="vars">$this</span><span>->result)) {   </span>
</li>
<li class="alt">
<span>　</span><span class="keyword">throw</span><span> </span><span class="keyword">new</span><span> Exception(</span><span class="string">'Query not executed.'</span><span>);   </span>
</li>
<li><span>}   </span></li>
<li class="alt"><span> </span></li>
<li>
<span></span><span class="keyword">return</span><span> </span><span class="vars">$this</span><span>->db->fetch_row(</span><span class="vars">$this</span><span>->result);   </span>
</li>
<li class="alt"><span>　}   </span></li>
<li><span> </span></li>
<li class="alt">
<span>　</span><span class="keyword">public</span><span> </span><span class="keyword">function</span><span> fetch_assoc()   </span>
</li>
<li><span>　{   </span></li>
<li class="alt">
<span></span><span class="keyword">if</span><span> (! </span><span class="func">is_resource</span><span>(</span><span class="vars">$this</span><span>->result)) {   </span>
</li>
<li>
<span>　</span><span class="keyword">throw</span><span> </span><span class="keyword">new</span><span> Exception(</span><span class="string">'Query not executed.'</span><span>);   </span>
</li>
<li class="alt"><span>}   </span></li>
<li><span> </span></li>
<li class="alt">
<span></span><span class="keyword">return</span><span> </span><span class="vars">$this</span><span>->db->fetch_assoc(</span><span class="vars">$this</span><span>->result);   </span>
</li>
<li><span>　}   </span></li>
<li class="alt"><span> </span></li>
<li>
<span>　</span><span class="keyword">public</span><span> </span><span class="keyword">function</span><span> fetch_object()   </span>
</li>
<li class="alt"><span>　{   </span></li>
<li>
<span></span><span class="keyword">if</span><span> (! </span><span class="func">is_resource</span><span>(</span><span class="vars">$this</span><span>->result)) {   </span>
</li>
<li class="alt">
<span>　</span><span class="keyword">throw</span><span> </span><span class="keyword">new</span><span> Exception(</span><span class="string">'Query not executed.'</span><span>);   </span>
</li>
<li><span>}   </span></li>
<li class="alt"><span> </span></li>
<li>
<span></span><span class="keyword">return</span><span> </span><span class="vars">$this</span><span>->db->fetch_object(</span><span class="vars">$this</span><span>->result);   </span>
</li>
<li class="alt"><span>　}   </span></li>
<li><span> </span></li>
<li class="alt">
<span>　</span><span class="keyword">public</span><span> </span><span class="keyword">function</span><span> num_rows()   </span>
</li>
<li><span>　{   </span></li>
<li class="alt">
<span></span><span class="keyword">if</span><span> (! </span><span class="func">is_resource</span><span>(</span><span class="vars">$this</span><span>->result)) {   </span>
</li>
<li>
<span>　</span><span class="keyword">throw</span><span> </span><span class="keyword">new</span><span> Exception(</span><span class="string">'Query not executed.'</span><span>);   </span>
</li>
<li class="alt"><span>}   </span></li>
<li><span> </span></li>
<li class="alt">
<span></span><span class="keyword">return</span><span> </span><span class="vars">$this</span><span>->db->num_rows(</span><span class="vars">$this</span><span>->result);   </span>
</li>
<li><span>　}   </span></li>
<li class="alt"><span>}  </span></li>
</ol>

The implementation of each function is quite simple. It first checks to make sure the query has been executed, then delegates the task to the DB object, returning its results as if it were the query object itself (called a basic database function). 1

http://www.bkjia.com/PHPjc/446623.htmlwww.bkjia.comtruehttp: //www.bkjia.com/PHPjc/446623.htmlTechArticle1. DBQuery Object Now, our DBQuery object simply imitates a stored procedure—once executed, it returns a The resulting resource must be saved; and if you want to use that...