Php类中的null变量 - null variable in Php class

null variable in Php class

本文关键字：null 变量 Php | 更新日期: 2023-09-27

我是php的新手，所以我有一个非常仔细研究的问题。我试着写一些能帮助我使用DB的类。此处编码：

<?php
    class DbHelper{
        private $databaseURL;
        private $databaseUName;
        private $databasePWord;
        private $databaseName;
        private $nameOfDbWithWorkers;
        private $connection;
        function __construct($dbURL, $dbUserName, $dbPword, $dbName, $nameOfDbWithWorkers){
            $this->databaseURL = $dbURL;
            $this->databaseUName = $dbUserName;
            $this->databasePWord = $dbPword;
            $this->databaseName = $dbName;
            $this->nameOfDbWithWorkers = $nameOfDbWithWorkers;
        }
        function setConnectionToDb(){
            $connection = mysql_connect($this->databaseURL,$this->databaseUName,$this->databasePWord) OR DIE("can't connect to DB"); 
            mysql_select_db($this->databaseName, $connection)or die ("Error while connecting to database");
        }
        function getUser($login, $pass){
            $query = "SELECT type FROM $this->nameOfDbWithWorkers WHERE login = '$login' and password = '$pass';"; 
            $queryResult = $this->getDataFromDbByQuery($query);
            echo $queryResult;
            if ((mysql_affected_rows($connection) == 1)){
                $meta = mysql_fetch_assoc($queryResult);
                if ($meta['type']=='admin'){
                    return 'admin';
                }
                if ($meta['type']=='user'){
                    return 'user';
                }
                else{
                    return 'nomatch';
                }
            }
            else{               
                 return 'nomatch';
            }           
        }
        function getDataFromDbByQuery($query){
            $this->setConnectionToDb();
            $result = mysql_query($query);
            mysql_close($connection);
            return $result;
        }
}
?>

我调用了getUser方法，但在getUser方法和getDataFromDbByQuery中有一个问题-$connection = null。为什么会这样？

因为一个简单变量总是局部的（除了使用global使其全局，但不要习惯于此；）。你可能正在寻找的是一处房产。您已经定义了private $connection，但只在方法中使用了$connection，您没有使用它，而是试图访问未定义的局部变量

    function setConnectionToDb(){
        $this->connection = mysql_connect($this->databaseURL,$this->databaseUName,$this->databasePWord) OR DIE("can't connect to DB"); 
        mysql_select_db($this->databaseName, $this->connection)or die ("Error while connecting to database");
    }
    //..
    function getUser($login, $pass){
        $query = "SELECT type FROM $this->nameOfDbWithWorkers WHERE login = '$login' and password = '$pass';"; 
        $queryResult = $this->getDataFromDbByQuery($query);
        echo $queryResult;
        if ((mysql_affected_rows($this->connection) == 1)){
            // ...
        }
    }

等等。只需将每个$connection替换为$this->connection即可。

尝试用$this->connection替换$connection。

$connection指的是一个局部作用域的变量，即在当前所在的函数之外不可用的变量。$this->connection指的是用private $connection定义的类的成员变量。