单例模式数据库连接

单例基础知识简介+案例

连接数据库时使用单例模式,避免造成对数据库反复连接造成的浪费!

主要分两部分

　　　　第一部分:数据库连接的单例

　　　　第二部分:DB类的调用

1.数据库的连接

<?php

    class Database
    {
        private $pdo;
        static $instance;
        private function __construct()
        {
　　　　　　　//此处用的是常量,可替换中自己对应的数据库
            $this->pdo = new PDO(DSN,USER,PWD);
        }
        private function __clone()
        {
        }
        public static function getInstance()
        {
            if(!(self::$instance instanceof self)){
                self::$instance = new self();
            }
            return self::$instance;
        }
        public function getPDO()
        {
            return $this->pdo;
        }
    }
    $database = Database::getInstance();
    $pdo = $database->getPDO();


 ?>

2.DB类调用连接

<?php


	// 数据库类,其他类都可用
	class DB
	{
		// pdo对象
		private $pdo;

		// 字段名
		private $field = '*';

		// 表名
		private $table;

		// 条件
		private $where;

		// 分组
		private $group;

		// 筛选
		private $having;

		// 排序
		private $order;

		// 分页
		private $limit;

		// sql源生语句
		public $sql;


		// 链接数据库
		public function __construct()
		{
			// $this->pdo = new PDO(DSN, USER, PWD);
			$database = Database::getInstance();
			$this->pdo = $database->getPDO();
		}


		// 查询数据
		public function select()
		{
			$this->sql = 'select '.$this->field.' from '.$this->table.$this->where.$this->group.$this->having.$this->order.$this->limit;


			$this->init();

			$res = $this->pdo->query($this->sql);

			if(is_object($res)){
				$data = $res->fetchAll(PDO::FETCH_ASSOC);
				return $data;
			}

			return false;
		}

		// 单数据查询
		public function find()
		{
			$this->sql = ' select '.$this->field.' from '.$this->table.$this->where;
			$this->init();

			$res = $this->pdo->query($this->sql);

			if(is_object($res)){
				$data = $res->fetch(PDO::FETCH_ASSOC);
				return $data;
			}

			return false;
		}

		// 删除数据
		public function delete()
		{
			$this->sql = 'delete from '.$this->table.$this->where.$this->order.$this->limit;
			$this->init();

			$res = $this->pdo->exec($this->sql);

			return $res;
		}

		// 插入数据
		public function insert($data = '')
		{
			if(!is_array($data)){
				return false;
			}

			// 准备sql
				$field = null;
				$value = null;

				// 拼接之前, 保证$data 里的数据 不用再调整
				foreach($data as $k => $v){
					$field .= '`'.$k.'`,';

					$value .= '"'.$v.'",';
				}

				$field = rtrim($field, ',');
				$value = rtrim($value, ',');

				$this->sql = 'insert into '.$this->table.' ( '.$field.' )  values('.$value.')';

			// 执行sql
				$res = $this->pdo->exec($this->sql);

				if($res){
					$newId = $this->pdo->lastInsertId();

					return $newId;
				}else{
					return false;
				}
		}

		// 更新数据
		public function update($data = '')
		{
			if(!is_array($data)){
				return false;
			}

			// 准备sql
				$str = null;

				// 拼接之前, 保证$data 里的数据 不用再调整
				foreach($data as $k => $v){
					$str .= '`'.$k.'`="'.$v.'"'.',';
				}

				$str = rtrim($str, ',');


				$this->sql = 'update '.$this->table.' set '.$str.$this->where;

				$this->init();

			// 执行sql
				$res = $this->pdo->exec($this->sql);
				if($res){
					return $res;
				}else{
					return false;
				}
		}


		public function field( $param  = '')
		{
			if( $param == '' ){
				$this->field = '*';
			}else{
				$this->field = $param;
			}

			return $this;
		}

		public function table($param = '')
		{
			$this->table = $param;

			return $this;
		}

		public function where($param = '')
		{
			if($param == ''){
				$this->where = null;
			}else{
				$this->where = ' where '.$param;
			}

			return $this;
		}

		public function group($param = '')
		{
			if($param == ''){
				$this->group = null;
			}else{
				$this->group = ' group by '.$param;
			}

			return $this;
		}

		public function having($param = '')
		{
			if($param == ''){
				$this->having = null;
			}else{
				$this->having = ' having '.$param;
			}

			return $this;
		}

		public function order($param = '')
		{
			if($param == ''){
				$this->order = null;
			}else{
				$this->order = ' order by '.$param;
			}

			return $this;
		}

		public function limit($param = '')
		{
			if($param == ''){
				$this->limit = null;
			}else{
				$this->limit = ' limit '.$param;
			}

			return $this;
		}

		// 初始化所有字段
		public function init()
		{
			$this->field = '*';
			$this->table = null;
			$this->where = null;
			$this->group = null;
			$this->having = null;
			$this->order = null;
			$this->limit = null;
		}
	}






 ?>