封装一个db类，用来专门操作数据库，以后凡是对数据库的操作，都由db类的对象来实现。这样有了自己的db类，写项目时简单的sql语句就不用每次写了，直接调用就行，很方便！
1.封装一个DB类。一个类文件应该只有一个类，其他的内容全部都没有。类文件的命名规则：类名.class.php
下面是创建DB类的代码：
<?<span>php
</span><span>//</span><span>封装一个DB类，用来专门操作数据库，以后凡是对数据库的操作，都由DB类的对象来实现</span>
<span>class</span><span> DB{
</span><span>//</span><span>属性</span>
<span>private</span> <span>$host</span><span>;
</span><span>private</span> <span>$port</span><span>;
</span><span>private</span> <span>$user</span><span>;
</span><span>private</span> <span>$pass</span><span>;
</span><span>private</span> <span>$dbname</span><span>;
</span><span>private</span> <span>$charset</span><span>;
</span><span>private</span> <span>$prefix</span>; <span>//</span><span>表前缀</span>
<span>private</span> <span>$link</span>; <span>//</span><span>连接资源（连接数据库，一般会返回一个资源，所以需要定义一个link属性）
//构造方法(作用：为了初始化对象的属性)，会被自动调用</span>
<span>/*</span><span>
* @param1 array $arr，默认为空，里面是一个关联数组，里面有7个元素
* array('host' => 'localhost','port' => '3306');
</span><span>*/</span>
<span>public</span> <span>function</span> __construct(<span>$arr</span> = <span>array</span><span>()){
</span><span>//</span><span>初始化</span>
<span>$this</span>->host = <span>isset</span>(<span>$arr</span>['host']) ? <span>$arr</span>['host'] : 'localhost';<span>//</span><span>先判断是否有自己的host，如果有就用自己的host，否则就使用默认的localhost</span>
<span>$this</span>->port = <span>isset</span>(<span>$arr</span>['port']) ? <span>$arr</span>['port'] : '3306'<span>;
</span><span>$this</span>->user = <span>isset</span>(<span>$arr</span>['user']) ? <span>$arr</span>['user'] : 'root'<span>;
</span><span>$this</span>->pass = <span>isset</span>(<span>$arr</span>['pass']) ? <span>$arr</span>['pass'] : 'root'<span>;
</span><span>$this</span>->dbname = <span>isset</span>(<span>$arr</span>['dbname']) ? <span>$arr</span>['dbname'] : 'mydatabase'<span>;
</span><span>$this</span>->charset = <span>isset</span>(<span>$arr</span>['charset']) ? <span>$arr</span>['charset'] : 'utf8'<span>;
</span><span>$this</span>->prefix = <span>isset</span>(<span>$arr</span>['prefix']) ? <span>$arr</span>['prefix'] : ''<span>;
</span><span>//</span><span>连接数据库（类是要操作数据库，因此要连接数据库）</span>
<span>$this</span>-><span>connect();
</span><span>//</span><span>设置字符集</span>
<span>$this</span>-><span>setCharset();
</span><span>//</span><span>选择数据库</span>
<span>$this</span>-><span>setDbname();
}
</span><span>/*</span><span>
* 连接数据库
</span><span>*/</span>
<span>private</span> <span>function</span><span> connect(){
</span><span>//</span><span>mysql扩展连接</span>
<span>$this</span>->link = <span>mysql_connect</span>(<span>$this</span>->host . ':' . <span>$this</span>->port,<span>$this</span>->user,<span>$this</span>-><span>pass);
</span><span>//</span><span>判断结果</span>
<span>if</span>(!<span>$this</span>-><span>link){
</span><span>//</span><span>结果出错了
//暴力处理，如果是真实线上项目（生产环境）必须写入到日志文件</span>
<span>echo</span> '数据库连接错误：<br/>'<span>;
</span><span>echo</span> '错误编号' . <span>mysql_errno</span>() . '<br/>'<span>;
</span><span>echo</span> '错误内容' . <span>mysql_error</span>() . '<br/>'<span>;
</span><span>exit</span><span>;
}
}
</span><span>/*</span><span>
* 设置字符集
</span><span>*/</span>
<span>private</span> <span>function</span><span> setCharset(){
</span><span>//</span><span>设置</span>
<span>$this</span>->db_query("set names {<span>$this</span>->charset}"<span>);
}
</span><span>/*</span><span>
* 选择数据库
</span><span>*/</span>
<span>private</span> <span>function</span><span> setDbname(){
</span><span>$this</span>->db_query("use {<span>$this</span>->dbname}"<span>);
}
</span><span>/*</span><span>
* 增加数据
* @param1 string $sql，要执行的插入语句
* @return boolean，成功返回是自动增长的ID，失败返回FALSE
</span><span>*/</span>
<span>public</span> <span>function</span> db_insert(<span>$sql</span><span>){
</span><span>//</span><span>发送数据</span>
<span>$this</span>->db_query(<span>$sql</span><span>);
</span><span>//</span><span>成功返回自增ID</span>
<span>return</span> <span>mysql_affected_rows</span>() ? <span>mysql_insert_id</span>() : <span>FALSE</span><span>;
}
</span><span>/*</span><span>
* 删除数据
* @param1 string $sql，要执行的删除语句
* @return Boolean，成功返回受影响的行数，失败返回FALSE
</span><span>*/</span>
<span>public</span> <span>function</span> db_delete(<span>$sql</span><span>){
</span><span>//</span><span>发送SQL</span>
<span>$this</span>->db_query(<span>$sql</span><span>);
</span><span>//</span><span>判断结果</span>
<span>return</span> <span>mysql_affected_rows</span>() ? <span>mysql_affected_rows</span>() : <span>FALSE</span><span>;
}
</span><span>/*</span><span>
* 更新数据
* @param1 string $sql，要执行的更新语句
* @return Boolean，成功返回受影响的行数，失败返回FALSE
</span><span>*/</span>
<span>public</span> <span>function</span> db_update(<span>$sql</span><span>){
</span><span>//</span><span>发送SQL</span>
<span>$this</span>->db_query(<span>$sql</span><span>);
</span><span>//</span><span>判断结果</span>
<span>return</span> <span>mysql_affected_rows</span>() ? <span>mysql_affected_rows</span>() : <span>FALSE</span><span>;
}
</span><span>/*</span><span>
* 查询：查询一条记录
* @param1 string $sql，要查询的SQL语句
* @return mixed，成功返回一个数组，失败返回FALSE
</span><span>*/</span>
<span>public</span> <span>function</span> db_getRow(<span>$sql</span><span>){
</span><span>//</span><span>发送SQL</span>
<span>$res</span> = <span>$this</span>->db_query(<span>$sql</span><span>);
</span><span>//</span><span>判断返回</span>
<span>return</span> <span>mysql_num_rows</span>(<span>$res</span>) ? <span>mysql_fetch_assoc</span>(<span>$res</span>) : <span>FALSE</span><span>;
}
</span><span>/*</span><span>
* 查询：查询多条记录
* @param1 string $sql，要查询的SQL语句
* @return mixed，成功返回一个二维数组，失败返回FALSE
</span><span>*/</span>
<span>public</span> <span>function</span> db_getAll(<span>$sql</span><span>){
</span><span>//</span><span>发送SQL</span>
<span>$res</span> = <span>$this</span>->db_query(<span>$sql</span><span>);
</span><span>//</span><span>判断返回</span>
<span>if</span>(<span>mysql_num_rows</span>(<span>$res</span><span>)){
</span><span>//</span><span>循环遍历</span>
<span>$list</span> = <span>array</span><span>();
</span><span>//</span><span>遍历</span>
<span>while</span>(<span>$row</span> = <span>mysql_fetch_assoc</span>(<span>$res</span><span>)){
</span><span>$list</span>[] = <span>$row</span><span>;
}
</span><span>//</span><span>返回</span>
<span>return</span> <span>$list</span><span>;
}
</span><span>//</span><span>返回FALSE</span>
<span>return</span> <span>FALSE</span><span>;
}
</span><span>/*</span><span>
* mysql_query错误处理
* @param1 string $sql，需要执行的SQL语句
* @return mixed，只要语句不出错，全部返回
</span><span>*/</span>
<span>private</span> <span>function</span> db_query(<span>$sql</span><span>){
</span><span>//</span><span>发送SQL</span>
<span>$res</span> = <span>mysql_query</span>(<span>$sql</span><span>);
</span><span>//</span><span>判断结果</span>
<span>if</span>(!<span>$res</span><span>){
</span><span>//</span><span>结果出错了
//暴力处理，如果是真实线上项目（生产环境）必须写入到日志文件</span>
<span>echo</span> '语句出现错误：<br/>'<span>;
</span><span>echo</span> '错误编号' . <span>mysql_errno</span>() . '<br/>'<span>;
</span><span>echo</span> '错误内容' . <span>mysql_error</span>() . '<br/>'<span>;
</span><span>exit</span><span>;
}
</span><span>//</span><span>没有错误</span>
<span>return</span> <span>$res</span><span>;
}
</span><span>//</span><span>__sleep方法</span>
<span>public</span> <span>function</span><span> __sleep(){
</span><span>//</span><span>返回需要保存的属性的数组</span>
<span>return</span> <span>array</span>('host','port','user','pass','dbname','charset','prefix'<span>);
}
</span><span>//</span><span>__wakeup方法</span>
<span>public</span> <span>function</span><span> __wakeup(){
</span><span>//</span><span>连接资源</span>
<span>$this</span>-><span>connect();
</span><span>//</span><span>设置字符集和选中数据库</span>
<span>$this</span>-><span>setCharset();
</span><span>$this</span>-><span>setDbname();
}
</span><span>/*</span><span>
* 获取完整的表名
</span><span>*/</span>
<span>protected</span> <span>function</span><span> getTableName(){
</span><span>//</span><span>完整表名：前缀+表名</span>
<span>return</span> <span>$this</span>->prefix . <span>$this</span>-><span>table;
}
}
</span><span>//</span><span>这个DB类，一般不写析构（不释放资源） </span>2.使用DB类，但是如果要使用某一个类来创建对象，必须要保证该类已经被加载到代码区里。可以使用一个魔术函数来实现对类的自动加载
自动加载：当一个脚本文件在执行某些语句的时候（实例化）需要去代码区里寻找对应的类，如果找不到会通过自动加载函数来将对应的类文件进行加载。
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魔术函数：__autoload()
比如我们在index.php页面中需要使用DB类，那么我们就直接调用即可，具体代码如下：
<?<span>php
</span><span>//</span><span>使用DB类的对象来访问数据库
//先加载类文件
//include_once 'DB.class.php';
//如果想使用其他类，又需要加载（所以使用魔术函数__autoload来实现类的自动加载）
//显示的写出魔术函数__autoload
//参数：需要加载的类的名字</span>
<span>function</span> __autoload(<span>$a</span><span>){
</span><span>//</span><span>将对应的类文件加载进来</span>
<span>if</span>(<span>is_file</span>("<span>$a</span>.class.php"<span>)){
</span><span>include_once</span> "<span>$a</span>.class.php"<span>;
}
}
</span><span>//</span><span>实例化</span>
<span>$db</span> = <span>new</span> DB(<span>array</span>('dbname' => 'mydatabase'<span>));
</span>
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