php - 具有 pdo 的数据库类，在继承时不应重新启动连接

Question

当我一次调用不同的模型然后多次建立数据库连接时，我只想要一个，这可能吗？下面是我的 mvc 的一部分

class Database{
    private $db;
    private $stmt;
    function __construct()
    {
        parent::__construct();
        $root = dirname(dirname(__FILE__));
        $this->config = parse_ini_file($root . '/app/config.ini', true);

        $db = $this->config['database settings'];
        $host = $db['host'];
        $user = $db['user'];
        $pword = $db['pword'];
        $db_name = $db['db'];
        $this->db = new PDO("mysql:host=$host;dbname=$db_name", $user, $pword, array(
            PDO::MYSQL_ATTR_FOUND_ROWS => true, PDO::ATTR_PERSISTENT => true
        ));
        $this->db->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
        $this->db->setAttribute(PDO::ATTR_EMULATE_PREPARES, false);        
    }
    function executeQuery($query, $params = array())
    {
         $this->stmt = $this->db->prepare($query);
         if (! ($this->stmt)) {
           throw new Exception('Query failed while preparing');
         }
         try {
            $this->stmt->execute($params);
         } catch (PDOException $e) {
            throw $e;
         }
     }
     function getRecords($query, $params = array(), $array = false, $all = false)
     {
          $this->executeQuery($query, $params);

           $records = array();
          if ($this->totalRecords() > 0) {
             if ($array) {
                $this->stmt->setFetchMode(PDO::FETCH_ASSOC);
             } else {
                 $this->stmt->setFetchMode(PDO::FETCH_OBJ);
             }
            if ($all) {
               $records = $this->stmt->fetchAll();
            } else {
                while (($record = $this->stmt->fetch()) !== false) {
                   $records[] = $record;
               }
           }
        }
        return $records;
     }
  }

下面是我使用的模型

class TestModel extends Database{
  function __construct(){
    parent::__construct();
  }
  function getUsers(){
     return $this->getRecords("SELECT * FROM users");
  }
}

下面是另一个模型，我想调用方法 getusers 以将其用于某些目的。

require("path_to_testmodel"); 
require("path_to_some_model");
require("path_to_some_other_model");
class TestModel2 extends Database{
    function __construct(){
       parent::__construct();
       $this->test_model = new TestModel();
       $this->some_model = new SomeModel();
       $this->some_other_model = new SomeOtherModel();
    }
    function doSomething(){
       $users = $this->test_model->getUsers();
    }
}

如果我在其中一个模型中包含多个模型，如 TestModel()，这里会看到每次建立数据库连接时，有时我会遇到连接过多错误，或者在某些系统中我会遇到内存分配问题。

请帮我解决这个问题。

Answer 1

尝试在 static property 中保存您的数据库连接.

class Database{
    static private $theOnlyConnection = null;
    private $db;
    private $stmt;

    public function __construct()
    {
        parent::__construct(); // Database has no parent, what is this line for?
        if(null === self::$theOnlyConnection) {
            $root = dirname(dirname(__FILE__));
            $config = parse_ini_file($root . '/app/config.ini', true);

            $db = $config['database settings'];
            $host = $db['host'];
            $user = $db['user'];
            $pword = $db['pword'];
            $db_name = $db['db'];
            self::$theOnlyConnection = new PDO("mysql:host=$host;dbname=$db_name", $user, $pword, array(
                PDO::MYSQL_ATTR_FOUND_ROWS => true, PDO::ATTR_PERSISTENT => true
            ));
            self::$theOnlyConnection->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
            self::$theOnlyConnection->setAttribute(PDO::ATTR_EMULATE_PREPARES, false);        
        }

        $this->db = self::$theOnlyConnection;
    }

请注意，这将导致连接在脚本结束时关闭，而不是在对象销毁时关闭。对于大多数用例来说都可以，但是如果您想更早地断开与数据库的连接，则需要跟踪您拥有的对象数量并在数量为 0 时销毁连接。

class Database{
    static private $theOnlyConnection = null;
    static private $modelObjectCount = 0;
    private $db;
    private $stmt;

    public function __construct()
    {
        self::$modelObjectCount++;
        if(null === self::$theOnlyConnection) {
            // connect
        }

        $this->db = self::$theOnlyConnection;
    }

    public function __destruct() {
        self::$modelObjectCount--;
        if(0 == self::$modelObjectCount) {
            // close connection
            self::$theOnlyConnection = null;
        }
    }