对PDO的封装

class Mysql{    static private $db; //数据引擎对象    private $pdo;  //pdo 引擎对象    private $table; //表名    private $where = array("1=1");//条件    private $data;//源数据    //定义受保护的构造方法禁止外部使用    private function __construct()    {        $this->pdo = new PDO("mysql:host=127.0.0.1;dbname=book",'root','');        //$this->pdo->query("set names utf8");    }    //初始化mysql类、在类内部实例化mysql类    static public function init(){        //自身调用需使用self::调用自身、判断是否被实例化        if(!self::$db){            self::$db = new Mysql();         }        //已被实例化直接返回、外部即可直接使用        return self::$db;    }    //原生SQL语句 直接执行；    public function query($sql)     {        //echo $sql.'<br>';        $ch =  $this->pdo->query($sql);        return $ch;    }    //查询多条    public function select($table='',$data=array(),$limit=array()){        //表名        if(!empty($table)) $this->table($table);        //条件        if(!empty($data)) $this->where($data);        //拼接where条件        $where = implode(' AND ',$this->where);        $limit_str = '';        //偏移量        if($limit){            $limit_str = ' LIMIT '.$limit[0].','.$limit[1];         }        $sql = 'SELECT * FROM '.$this->table.' WHERE '.$where.$limit_str;        //echo $sql;        //绑定参数        //dump($this->data);        $item = $this->bind($sql,$this->data);        //dump($item);        $item->setFetchMode(PDO::FETCH_ASSOC);        $data = $item->fetchAll();        return $data;    }    //添加    public function add($table,$data=array())     {        //获取添加的表名        $this->table = $table;        //echo $this->table;die;        $data = $this->redun($data);       // dump($data);        //循环数据 生成 $key , $val ;        $val = '';        $key = '';        foreach ($data as $k => $v) {            $key .= $k.',';            $val .= ':'.$k.',';        }        $val = trim($val,',');        $key = trim($key,',');        $sql = "INSERT INTO ".$table. '('.$key.') VALUES ('.$val.')';        //echo $sql;die;        //绑定参数        $this->bind($sql,$data);        //获取新插入的id        return $this->pdo->lastInsertId();    }    public function del($table,$data=array()){        //获取删除的表名        $this->table = $table;        $field=$this->field();        $data = $this->redun($data);        $sql = "delete from ".$table." where ". $field[0] ." in ( :".$field[0] .')';        //绑定参数        $ch = $this->bind($sql,$data);        return $ch->rowCount();    }    public function save($table,$data=array()){        //获取修改的表名        $this->table = $table;        //        $data = $this->redun($data);        $field=$this->field();        //拼接where条件        if(isset($data[$field[0]])){            $where = ' where '.$field[0].' = :'.$field[0];        }        $sql = 'UPDATE '.$this->table . ' SET ';        foreach ($data as $k => $v) {            if ($k == $field[0]) continue;                $sql .= $k ." = :".$k.",";        }        //echo $sql;        $sql = trim($sql,',').$where;        //绑定参数         $ch = $this->bind($sql,$data);         return $ch->rowCount();    }    //where条件    public function where($data = array()){        if (is_array($data)) {            //把数据存入             $this->data = $data;            $this->where[] = " 1=1 ";            foreach ($data as $key => $val){                $this->where[] = $key.'=:'.$key;            }        }        if (is_string($data) && !empty($data)) {            $arr = explode(' ',$data);            $val  = trim($arr[2] , "'");            $this->where[] = $arr[0].' '.$arr[1].' :'.$arr[0];            $this->data[$arr[0]] = $val;        }        return $this;    }    //表名    public function table($table = ''){        $this->table = $table;        return $this;    }    public function bind($sql, $data=array()) {    $ch= $this->pdo->prepare($sql);    if(!empty ($data)){        foreach($data as $key=>$val){            $ch->bindValue(':'.$key, $val);            }        }    //执行返回状态    //dump($sql);    $ch->execute();    //$ch->debugDumpParams();    return $ch;    }    //查询表中字段    public function field(){        //dump($this->pdo);        $ch = $this->pdo->query('desc '.$this->table);        //echo $this->table;        $data = $ch->fetchAll(PDO::FETCH_ASSOC);        $arr = array();        foreach($data as $val){            $arr[] = $val['Field'];        }        return $arr;    }    public function redun($data=array()) {        //获取表字段        $field=$this->field();        //循环去除重复字段        foreach($data as $key=>$val){            if(!in_array($key, $field)) {                unset ($data[$key]);            }        }        return $data;    }}