将php代码从mysql更新为mysqli，未定义的变量，但在构造函数中定义

Question

I downloaded this code from androidhive. It's login/registration code for android apps. Now the php code is from two years ago and so I was originally gettin depreciated errors and so I began updating the code to mysqli.So far when converting, I've been changing the mysql functions to mysqli, and if need be adjusting the parameters. I'm fairly new to php in general so I've been running into a few problems, the main one being that of isUserExisted function in DB_functions the variable db is undefined for the mysqli_query. I'm not sure why I'm getting this error because I've defined it in the constructor. I've looked at similar questions and the answers that fixed their problems were usually syntax errors, which when I compare this code, I don't seem to have. Any help would be greatly appreciated. Here's the DB_Functions.php and the DB_Connect.php respectively:

<?php

class DB_Functions {

    private $db = null;

    //put your code here
    // constructor
    function __construct() {
        require 'DB_Connect.php';
        
        // connecting to database
        $this->db = new DB_Connect();
        $this->db->connectThis();
        
    }

    // destructor
    function __destruct() {
        
    }

    /**
     * Storing new user
     * returns user details
     */
    public function storeUser($name, $email, $password) {
        $uuid = uniqid('', true);
        $hash = $this->hashSSHA($password);
        $encrypted_password = $hash["encrypted"]; // encrypted password
        $salt = $hash["salt"]; // salt
        $result = mysqli_query($db,"INSERT INTO users(unique_id, name, email, encrypted_password, salt, created_at) VALUES('$uuid', '$name', '$email', '$encrypted_password', '$salt', NOW())");
        // check for successful store
        if ($result) {
            // get user details 
            $uid = mysqli_insert_id(); // last inserted id
            $result = mysqli_query($db,"SELECT * FROM users WHERE uid = $uid");
            // return user details
            return mysqli_fetch_array($result);
        } else {
            return false;
        }
    }

    /**
     * Get user by email and password
     */
    public function getUserByEmailAndPassword($email, $password) {
        $result = mysqli_query($db,"SELECT * FROM users WHERE email = '$email'") or die(mysql_error());
        // check for result 
        $no_of_rows = mysqli_num_rows($result);
        if ($no_of_rows > 0) {
            $result = mysqli_fetch_array($result);
            $salt = $result['salt'];
            $encrypted_password = $result['encrypted_password'];
            $hash = $this->checkhashSSHA($salt, $password);
            // check for password equality
            if ($encrypted_password == $hash) {
                // user authentication details are correct
                return $result;
            }
        } else {
            // user not found
            return false;
        }
    }

    /**
     * Check user is existed or not
     */
    public function isUserExisted($email) {
        $result = mysqli_query($db,"SELECT email from users WHERE email = '$email'");
        $no_of_rows = mysqli_num_rows($result);
        if ($no_of_rows > 0) {
            // user existed 
            return true;
        } else {
            // user not existed
            return false;
        }
    }

    /**
     * Encrypting password
     * @param password
     * returns salt and encrypted password
     */
    public function hashSSHA($password) {

        $salt = sha1(rand());
        $salt = substr($salt, 0, 10);
        $encrypted = base64_encode(sha1($password . $salt, true) . $salt);
        $hash = array("salt" => $salt, "encrypted" => $encrypted);
        return $hash;
    }

    /**
     * Decrypting password
     * @param salt, password
     * returns hash string
     */
    public function checkhashSSHA($salt, $password) {

        $hash = base64_encode(sha1($password . $salt, true) . $salt);

        return $hash;
    }

}

?>

<?php
class DB_Connect {
    

    // constructor
    function __construct() {
        
    }

    // destructor
    function __destruct() {
        // $this->close();
    }

    // Connecting to database
    public function connectThis() {
        require 'include/Config.php';
        // connecting to mysql
        $db = mysqli_connect(DB_HOST, DB_USER, DB_PASSWORD, DB_DATABASE) or die(mysqli_error());
        // selecting database

        // return database handler
        return $db;
    }

    // Closing database connection
    public function close() {
        mysqli_close();
    }

}

?>

</div>

Answer 1

You need to call it like this:

$result = mysqli_query($this->db,"SELECT email from users WHERE email = '$email'");