```php
<?php
/*
*** PHP5 简单的PDO类封装链式调用
*** 作者：小黄牛
*** 简化常用查询
*** 完整的链式封装已经完成，并且用在了我最近开发的小型框架——JunPHP中作为Model模型底层。这样就将其中最简单的一部分查询操作先开源给大家学习下
*/

/*
链式操作一般有：
where 查询条件
field 指定查询结果集中的返回字段
order 排序
limit 限制查询结果

结尾方法：
 
select 执行查询返回二维数组
find   执行查询，只能返回一条数据，返回一维数组
*/
 
header("Content-type: text/html; charset=utf-8");//声明PHP编码
$C = array(
	//数据库以及系统公用参数
	"DB_TYPE"               =>  "mysql",     // 数据库类型
	"DB_HOST"               =>  "localhost", // 服务器地址
	"DB_NAME"               =>  "page",      // 数据库名
	"DB_USER"               =>  "root",   // 用户名
	"DB_PWD"                =>  "",       // 密码
	"DB_PORT"               =>  "3306",       // 端口
	"DB_PREFIX"             =>  "",    // 数据库表前缀
	"DB_CHARSET"            =>  "utf8",   // 数据库编码
);
 
//Model模型底层
class Model{
	protected $dbMs;          //数据库类型
	protected $dbHost;        //数据库主机名
        protected $dbName;        //数据库名称
	protected $dbCharset;     //数据库编码
	protected $dbUser;        //数据库连接用户名
	protected $dbPwd;         //对应的密码
        protected $tablePrefix;   //数据表前缀
        protected $tableName;     //数据表名（不包含表前缀)
	protected $trueTableName; //数据表名(已包含表前缀)
	protected $dbSql;         //记录需要执行的SQL语句
	protected $linkOperation = array(
			'field' => '*',
			'where' => '',
			'order' => '',
			'limit' => '',
		 ); //连贯操作参数
	private $instance;        //数据库PDO连接实例
 
	//构造方法
	public function __construct(){
		global $C;//获得配置信息
		$this->dbMs         = $C['DB_TYPE'];
		$this->dbHost       = $C['DB_HOST'];
		$this->dbName       = $C['DB_NAME'];
		$this->dbCharset    = $C['DB_CHARSET'];
		$this->dbUser       = $C['DB_USER'];
		$this->dbPwd        = $C['DB_PWD'];
		$this->tablePrefix  = $C['DB_PREFIX'];
		$this->dbPdo();//初始化PDO类
	}
 
        //数据库连接
	private function dbPdo(){
		$dbn = $this->dbMs.':host='.$this->dbHost.';dbname='.$this->dbName.';charset='.$this->dbCharset;
		$dbh = new PDO($dbn,$this->dbUser,$this->dbPwd);
		$this->instance = $dbh;
	}
 
	//拼接Sql
	private function dbSqli(){
		$where = !empty($this->linkOperation['where'])?' where '.$this->linkOperation['where']:'';
		$order = !empty($this->linkOperation['order'])?' order by '.$this->linkOperation['order']:''; 
		$limit = !empty($this->linkOperation['limit'])?' limit '.$this->linkOperation['limit']:''; 
		$sql = 'select '.$this->linkOperation['field'].' from '.$this->trueTableName.$where.$order.$limit;
		$this->dbSql = $sql;
	}
 
	//操作指定表名
	public function M($tableName){
		$this->trueTableName = $this->tablePrefix.$tableName;
		$this->tableName = $tableName;
		return $this;
	}
 
	//指定查询结果集中的返回字段
	public function field($name){
		$this->linkOperation['field'] = $name;
		return $this;
	}
 
	//指定字段排序
	public function order($name){
		$this->linkOperation['order'] = $name;
		return $this;
	}
 
	//查询条件
	public function where($name){
		$this->linkOperation['where'] = $name;
		return $this;
	}
 
	//查询分页
	public function limit($name){
		$this->linkOperation['limit'] = $name;
		return $this;
 
	}
 
	//执行SELECT查询获取单条记录，返回一维数组
	public function find(){
		$this->dbSqli();
		$pdo = $this->instance;
		$res = $pdo->query($this->dbSql);
		$res->setFetchMode(PDO::FETCH_NUM); //数字索引方式
		return $res->fetch();
	}
 
	//执行SELECT获取所有记录，返回二维数组
	public function select(){
		$this->dbSqli();
		$pdo = $this->instance;
		$res = $pdo->query($this->dbSql);
		$res->setFetchMode(PDO::FETCH_NUM); //数字索引方式
		$array = array();
		while ($row = $res->fetch()){
			$array[] = $row;
		}
		return $array;
	}
}
$db = new Model();
$res = $db->M('article')->order('id desc')->select();//返回查询结果的二维数组
$res = $db->M('article')->order('id asc')where('id=3')->find();//返回查询结果的一位数组，只能返回一条记录
```

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