属性拦截器以及查询构造器

1. 属性拦截器

<?php
// 属性重载，又叫属性拦截器
// 示例一：__get()：读取不可访问属性的值时自动调用
class Demo1
{
    public function __get($name)
    {
        return $name.'<br>';
    }
}
$obj1 = new Demo1();
echo $obj1->email;
echo $obj1->age;
echo '<hr>';
// 示例二：__set()：在给不可访问属性赋值时自动调用
class Demo2
{
    public function __set($name,$value)
    {
        echo $name.' : '.$value;
    }
}
$obj2 = new Demo2();
$obj2->username = '小明';
echo '<hr>';
// 示例三：__isset()：当对不可访问属性调用 isset() 或 empty() 时，__isset() 会被调用
class Demo3
{
    public $username = '孙悟空';
    public function __isset($name)
    {
        echo $name.' 存在吗？'.'<br>';
        return isset($this->$name);
    }
}
$obj3 = new Demo3();
var_dump(isset($obj3->username));
echo '<hr>';
var_dump(isset($obj3->email));
echo '<hr>';
// 示例四：__unset()：当对不可访问属性调用 unset（） 时，__unset() 会被调用
class Demo4
{
    public $num1 = 'aaa';
    private $num2 = 'bbb';
    public function __unset($name)
    {
        // 通过外部传参，可以输出私有成员$num2
        echo $this->$name,'<hr>';
        // 删除$num2变量
        unset($this->$name);
        // 现在就不能输出了，此时就能达到即使在外部也能访问私有成员，并操作它
        echo $this->$name,'<hr>';
    }
}
$obj4 = new Demo4();
// 实例化类得到对象，访问类中公共成员，然后删除$num1变量，没有问题
echo $obj4->num1,'<hr>';
unset($obj4->num1);
echo $obj4->num1,'<hr>';
// 但是不能访问私有成员，更别说在外部删除私有变量了，但是可以通过unset()去自动调用类中的__unset()魔术方法
// echo $obj4->num2;
unset($obj4->num2);

2. 查询构造器

操作的数据表如下：

2.1 select查询

<?php
// SELECT `字段` FROM `数据表` LIMIT `几条记录`
// 查询类
class Query
{
    // 1. 连接对象
    protected $pdo;
    // 2. 字段
    protected $field;
    // 3. 数据表名
    protected $table;
    // 4. 查询几条
    protected $limit;
    // 5. 连接数据库：使用构造方法
    public function __construct($dsn,$username,$password)
    {
        $this->connect($dsn,$username,$password);
    }
    private function connect($dsn,$username,$password)
    {
        $this->pdo = new PDO($dsn,$username,$password);
    }
    // 6. 设置默认查询字段。6,7,8步骤都设置return $this;是便于链式调用
    public function field ($field)
    {
        $this->field = $field;
        return $this;
    }
    // 7. 设置默认数据表名
    public function table ($table)
    {
        $this->table = $table;
        return $this;
    }
    // 8. 设置默认查询记录数量
    public function limit ($limit)
    {
        $this->limit = $limit;
        return $this;
    }
    // 9. 设置sql查询语句
    public function sql ()
    {
        return sprintf(' SELECT %s FROM %s LIMIT %s ', $this->field , $this->table , $this->limit);
    }
    // 10. 执行查询语句
    public function select ()
    {
        return $this->pdo->query($this->sql())->fetchAll(PDO::FETCH_ASSOC);
    }
}
// 数据库操作类
class DB
{
    public static function __callStatic ($name,$args)
    {
        $dsn = 'mysql:host=php.edu;dbname=first';
        $username = 'root';
        $password = 'root';
        $query = new Query($dsn,$username,$password);
        return call_user_func([$query,$name],...$args);
    }
}
$res = DB::table('student') -> field('username,sex,tel') -> limit(3) -> select();
if (!empty($res)) {
    $table = <<<EOF
       <table border=1>
          <tr>
              <td>姓名</td>
              <td>性别</td>
              <td>电话</td>
          </tr>
    EOF;
    foreach ( $res as $key=>$value ) {
        $table.="<tr>";
        $table.="<td>{$value['username']}</td>";
        $table.="<td>{$value['sex']}</td>";
        $table.="<td>{$value['tel']}</td>";
        $table.="</tr>";
    }
    $table.="</table>";
    echo $table;
}

2.2 insert插入

<?php
// INSERT INTO 数据表 （字段） VALUES （插入值）
class Query
{
    protected $pdo;
    protected $field;
    protected $table;
    protected $values;
    public function __construct($dsn,$username,$password)
    {
        $this->connect($dsn,$username,$password);
    }
    private function connect($dsn,$username,$password)
    {
        $this->pdo = new PDO($dsn,$username,$password);
    }
    public function field ($field)
    {
        $this->field = $field;
        return $this;
    }
    public function table ($table)
    {
        $this->table = $table;
        return $this;
    }
    public function values ($values)
    {
        $this->values = $values;
        return $this;
    }
    public function sql ()
    {
        return sprintf( " INSERT INTO %s (%s) VALUES (%s) ", $this->table , $this->field ,$this->values);
    }
    public function insert ()
    {   
        $this->pdo->query($this->sql());
    }
}
class DB
{
    public static function __callStatic ($name,$args)
    {
        $dsn = 'mysql:host=php.edu;dbname=first';
        $username = 'root';
        $password = 'root';
        $query = new Query($dsn,$username,$password);
        return call_user_func([$query,$name],...$args);
    }
}
DB::table('student') -> field('username,password,sex,age,tel') -> values("'哇哇','123456','男','50','15050355655'") -> insert();

2.3 update更新

<?php
// UPDATE 数据表 SET 字段1=value WHERE 字段2=where
class Query
{
    protected $pdo;
    protected $field;
    protected $set;
    protected $table;
    protected $value;
    protected $where;
    public function __construct($dsn,$username,$password)
    {
        $this->connect($dsn,$username,$password);
    }
    private function connect($dsn,$username,$password)
    {
        $this->pdo = new PDO($dsn,$username,$password);
    }
    public function set ($set)
    {
        $this->set = $set;
        return $this;
    }
    public function table ($table)
    {
        $this->table = $table;
        return $this;
    }
    public function value ($value)
    {
        $this->value = $value;
        return $this;
    }
    public function field ($field)
    {
        $this->field = $field;
        return $this;
    }
    public function where ($where)
    {
        $this->where = $where;
        return $this;
    }
    public function sql ()
    {
        return sprintf( " UPDATE %s SET %s = %s WHERE %s = %s", $this->table , $this->set , $this->value , $this->field , $this->where ) ;
    }
    public function update ()
    {   
        // var_dump($this->pdo->query($this->sql()));
        $this->pdo->query($this->sql());
    }
}
class DB
{
    public static function __callStatic ($name,$args)
    {
        $dsn = 'mysql:host=php.edu;dbname=first';
        $username = 'root';
        $password = 'root';
        $query = new Query($dsn,$username,$password);
        return call_user_func([$query,$name],...$args);
    }
}
DB::table('student') -> set('username') -> value("'老五'") -> field('id') -> where("'4'") -> update();

2.4 delete删除

<?php
// DELETE FROM 数据表 WHERE 字段=where
class Query
{
    protected $pdo;
    protected $field;
    protected $table;
    protected $where;
    public function __construct($dsn,$username,$password)
    {
        $this->connect($dsn,$username,$password);
    }
    private function connect($dsn,$username,$password)
    {
        $this->pdo = new PDO($dsn,$username,$password);
    }
    public function field ($field)
    {
        $this->field = $field;
        return $this;
    }
    public function table ($table)
    {
        $this->table = $table;
        return $this;
    }
    public function where ($where)
    {
        $this->where = $where;
        return $this;
    }
    public function sql ()
    {
        return sprintf( " DELETE FROM %s WHERE %s=%s ", $this->table , $this->field ,$this->where);
    }
    public function delete ()
    {   
       $this->pdo->query($this->sql());
    }
}
class DB
{
    public static function __callStatic ($name,$args)
    {
        $dsn = 'mysql:host=php.edu;dbname=first';
        $username = 'root';
        $password = 'root';
        $query = new Query($dsn,$username,$password);
        return call_user_func([$query,$name],...$args);
    }
}
DB::table('student') -> field('id') -> where("'1015'") -> delete();

3. 总结