php 图书类程序设计初始化文件

<!--图书类文件: class_book.php-->
<?php
    class book
    {
        private $id;
        private $name;
        private $price;
        private $author;

        function __construct()  //__construct：构造函数，建立连接
        {
            //$this->name=$name;
            //$this->price=$price;
            //$this->author=$author;
        }
        function __set($property_name,$value)
        {
            return $this->$property_name=$value;
        }
        function __get($property_name)
        {
            if(isset($this->$property_name))
            {
                return $this->$property_name;
            }
            else
            {
                return null;
            }
        }

        function add()          //添加书目
        {
            $db=new database();
            $query="INSERT INTO Computer (name,price,author) ";
            $query.="VALUES ('$this->name',$this->price,'$this->author')";
            $db->execute($query);
            $db=null;

        }
        function update()       //修改书目
        {
            $db=new database();
            $query="UPDATE Computer SET ";
            $query.="name='$this->name',price=$this->price,author='$this->author' ";
            $query.="WHERE id=$this->id";
            $db->execute($query);
            $db=null;

        }
        function delete()       //删除书目
        {
            $db=new database();
            $query="DELETE FROM Computer WHERE id=$this->id";
            $db->execute($query);
            $db=null;
        }
        static function query($condition)               //查询书目
        {
            if($condition=="" || $condition==null)
            $condition="";
            else
            $condition="WHERE ".$condition;
            $db=new database();
            $query="SELECT * FROM Computer ".$condition;
            $arr=$db->query($query);
            return $arr;
            $db=null;

        }

    }

/*
    $b=new book("C语言",15.20,"吴强");
    $b->add();
    //$b->__set(new_author,"3");
    //$b->update();
    //$b->delete();
    //*/
?>
//该片段来自于http://outofmemory.cn