方法鏈接覆蓋變量

Question

我已經實現了數據庫的鏈接方法。我的問題是，當我調用數據庫類時，它會覆蓋新的變量。我怎樣才能保存我的變量。這是我的代碼。

當我使用此代碼：

Database::('table') 
      ->set(['name', 'test']) 
      ->select([ 
      Database::('table2') 
       ->set(['name', 'test2')]) 
      ]); 

它覆蓋上Database::('table')->set和覆蓋使用新Database::('table2')->set變量$set變量。

數據庫類：

namespace VendorName; 

class Database 
{ 
    private static $reserved_words = [ 
     'NOW()', 'IS NOT NULL', 'IS NULL', 
    ]; 

    private static $connection = null; 
    private static $table = ''; 
    private static $join = ''; 
    private static $values = ''; 
    private static $set = ''; 
    private static $where = ''; 
    private static $show = null; 
    private static $select = null; 
    private static $order_by = ''; 
    private static $params = []; 

    /** 
    * Call the database table to be used. 
    * 
    * @param string $table 
    */ 
    public static function table($table) 
    { 
     self::$table .= $table; 

     return new static; 
    } 

    public static function set($set) 
    { 
     self::$set .= ' SET'; 

     $index = 0; 

     foreach ($set as $value) { 
      if ($index++ > 0) { 
       self::$set .= ', '; 
      } 

      if (in_array($value[1], self::$reserved_words)) { 
       self::$set .= " {$value[0]} = {$value[1]}"; 
      } else { 
       self::$set .= " {$value[0]} = ?"; 
      } 
     } 

     if (self::checkColumn('updated_at') && self::checkColumn('updated_by')) { 
      self::$set .= ', updated_at = NOW(), updated_by = ' . Authentication::getAuthenticatedUser(); 
     } 

     self::$params = array_merge(self::$params, $set); 

     return new static; 
    } 

    /** 
    * Create a WHERE query based on given parameters. 
    * 
    * @param array $where 
    */ 
    public static function where($where) 
    { 
     self::$where .= ' WHERE'; 

     $index = 0; 

     foreach ($where as $value) { 
      if ($index++ > 0) { 
       self::$where .= ' AND'; 
      } 

      if (in_array($value[1], self::$reserved_words)) { 
       self::$where .= " {$value[0]} {$value[1]}"; 
      } else { 
       self::$where .= " {$value[0]} {$value[1]} ?"; 
      } 
     } 

     self::$params = array_merge(self::$params, $where); 

     return new static; 
    } 

    /** 
    * select data from the database. 
    * 
    * @param array $columns 
    */ 
    public static function select($columns = ['*']) 
    { 
     self::$select = self::$connection->prepare('SELECT ' . implode(',', $columns) . ' FROM ' . self::$table . self::$join . self::$where . self::$order_by . self::$show); 

     $index = 1; 

     foreach (self::$params as $key => $value) { 
      if (!in_array($value[count($value) - 1], self::$reserved_words)) { 
       self::$select->bindValue($index++, $value[count($value) - 1]); 
      } 
     } 

     //echo 'SELECT ' . implode(',', $columns) . ' FROM ' . self::$table . self::$join . self::$where . self::$show; 

     self::$select->execute(); 

     return new static; 
    } 

    /** 
    * fetch data from the database. 
    * 
    * @return array 
    */ 
    public static function fetch() 
    { 
     $result = self::$select->fetch(); 

     self::clean(); 

     return $result; 
    } 

    /** 
    * fetch data as associative array from the database. 
    * 
    * @return array 
    */ 
    public static function fetchAll() 
    { 
     $result = self::$select->fetchAll(\PDO::FETCH_ASSOC); 

     self::clean(); 

     return $result; 
    } 
} 

Answer 1

它看起來像你想實現一個Singleton pattern設計。在這個設計中，類只能擁有一個實例，這是由類控制：

<?php 

class Database { 
    static private $singleton; 
    private $data; // Some other data members... 

    static public function getInstance() { 
     if (!isset(self::$singleton)) { 
      self::$singleton = new self; // works for derived classes also 
     } 

     return self::$singleton; 
    } 

    private function __construct() { 
     // Do some useful initialization... 
    } 

    public function chainedOperation($param) { 
     // Do some useful database operation... 
     echo "I did something useful with '$param'." . PHP_EOL; 

     return $this; 
    } 
} 

Database::getInstance()->chainedOperation('apple') 
         ->chainedOperation('pear') 
         ->chainedOperation('php'); 

// I cannot create a Database instance conventionally. 
// error: Call to private Database::__construct() from invalid context 
// $db = new Database;