用 PHP 走向动态6 --改进的空间

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对这个动态类我想做的最后一个改进，是用成员变量访问字段，而不是用笨重的 get_ 和 set_ 操作符。清单 7 显示了如何用 __get 和 __set 魔法方法代替 __call。


清单 7. 使用 __get 和 __set 方法

1. <?php
   
2. require_once("DB.php");
   
3. $dsn = 'mysql://root:password@localhost/bookdb';
   
4. $db =& DB::Connect( $dsn, array() );
   
5. if (PEAR::isError($db)) { die($db->getMessage()); }
   
6. class DBObject
   
7. {
   
8.   private $id = 0;
   
9.   private $table;
   
10.   private $fields = array();
    
11.   function __construct( $table, $fields )
    
12.   {
    
13.     $this->table = $table;
    
14.     foreach( $fields as $key )
    
15.       $this->fields[ $key ] = null;
    
16.   }
    
17.   function __get( $key )
    
18.   {
    
19.     return $this->fields[ $key ];
    
20.   }
    
21.   function __set( $key, $value )
    
22.   {
    
23.     if ( array_key_exists( $key, $this->fields ) )
    
24.     {
    
25.       $this->fields[ $key ] = $value;
    
26.       return true;
    
27.     }
    
28.     return false;
    
29.   }
    
30.   function load( $id )
    
31.   {
    
32.     global $db;
    
33.     $res = $db->query(
    
34.   "SELECT * FROM ".$this->table." WHERE ".
    
35.    $this->table."_id=?",
    
36.       array( $id )
    
37.     );
    
38.     $res->fetchInto( $row, DB_FETCHMODE_ASSOC );
    
39.     $this->id = $id;
    
40.     foreach( array_keys( $row ) as $key )
    
41.       $this->fields[ $key ] = $row[ $key ];
    
42.   }
    
43.   function insert()
    
44.   {
    
45.     global $db;
    
46.     $fields = $this->table."_id, ";
    
47.     $fields .= join( ", ", array_keys( $this->fields ) );
    
48.     $inspoints = array( "0" );
    
49.     foreach( array_keys( $this->fields ) as $field )
    
50.       $inspoints []= "?";
    
51.     $inspt = join( ", ", $inspoints );
    
52. $sql = "INSERT INTO ".$this->table.
    
53.    " ( $fields ) VALUES ( $inspt )";
    
54.     $values = array();
    
55.     foreach( array_keys( $this->fields ) as $field )
    
56.       $values []= $this->fields[ $field ];
    
57.     $sth = $db->prepare( $sql );
    
58.     $db->execute( $sth, $values );
    
59.     $res = $db->query( "SELECT last_insert_id()" );
    
60.     $res->fetchInto( $row );
    
61.     $this->id = $row[0];
    
62.     return $row[0];
    
63.   }
    
64.   function update()
    
65.   {
    
66.     global $db;
    
67.     $sets = array();
    
68.     $values = array();
    
69.     foreach( array_keys( $this->fields ) as $field )
    
70.     {
    
71.       $sets []= $field.'=?';
    
72.       $values []= $this->fields[ $field ];
    
73.     }
    
74.     $set = join( ", ", $sets );
    
75.     $values []= $this->id;
    
76. $sql = 'UPDATE '.$this->table.' SET '.$set.
    
77.   ' WHERE '.$this->table.'_id=?';
    
78.     $sth = $db->prepare( $sql );
    
79.     $db->execute( $sth, $values );
    
80.   }
    
81.   function delete()
    
82.   {
    
83.     global $db;
    
84.     $sth = $db->prepare(
    
85. 'DELETE FROM '.$this->table.' WHERE '.
    
86. $this->table.'_id=?'
    
87.     );
    
88.     $db->execute( $sth,
    
89.       array( $this->id ) );
    
90.   }
    
91.   function delete_all()
    
92.   {
    
93.     global $db;
    
94.     $sth = $db->prepare( 'DELETE FROM '.$this->table );
    
95.     $db->execute( $sth );
    
96.   }
    
97. }
    
98. class Book extends DBObject
    
99. {
    
100.   function __construct()
     
101.   {
     
102.   parent::__construct( 'book',
     
103.     array( 'author', 'title', 'publisher' ) );
     
104.   }
     
105. }
     
106. $book = new Book( );
     
107. $book->delete_all();
     
108. $book->{'title'} = "PHP Hacks";
     
109. $book->{'author'} = "Jack Herrington";
     
110. $book->{'publisher'} = "O'Reilly";
     
111. $id = $book->insert();
     
112. echo ( "New book id = $id\n" );
     
113. $book->{'title'} = "Podcasting Hacks";
     
114. $book->update();
     
115. $book2 = new Book( );
     
116. $book2->load( $id );
     
117. echo( "Title = ".$book2->{'title'}."\n" );
     
118. $book2->delete( );
     
119. ?>
     

复制代码

底部的测试代码只演示了这个语法干净了多少。要得到图书的书名，只需得到 title 成员变量。这个变量会调用对象的 __get 方法，在散列表中查找 title 条目并返回。

现在就得到了单个动态的数据库访问类，它能够让自己适应到数据库中的任何表。