PHP OOP boolean error - php

Question

I have got the following error:
Fatal error: Uncaught Error: Call to a member function count() on boolean in C:\xampp\htdocs\pianocourse101\index.php:5 Stack trace: #0 {main} thrown in C:\xampp\htdocs\pianocourse101\index.php on line 5
I have been wondering whether is the error part of my function count in my db.php or from index.php? Here is my code:
db.php
<?php
class DB {
private static $_instance = null;
private $_pdo,
$_query,
$_error = false,
$_results,
$_count = 0;
private function __construct() {
try {
$this->_pdo = new PDO('mysql:host='.Config::get('mysql/host').';dbname='.Config::get('mysql/db'), Config::get('mysql/username'),Config::get('mysql/password'));
} catch(PDOException $e) {
die($e->getMessage());
}
}
public static function getInstance() {
if(!isset(self::$_instance)) {
self::$_instance = new DB();
}
return self::$_instance;
}
public function query($sql, $params = array()) {
$this->_error = false;
// set the error to false so that we are not returning a previous error
if($this->_query = $this->_pdo->prepare($sql)) {
// check to see if query has been prepared properly
$x=1;
if(count($params)) { // check to see if need to bind
anything
foreach($params as $param) {
$this->_query->bindValue($x, $param);
$x++;
}
}
if($this->_query->execute()) {
$this->_results = $this->_query->fetchAll(PDO::FETCH_OBJ);
$this->_count = $this->_query->rowCount(); // to query a
database securely by binding parameters and preventing sql
injections
} else {
$this->_error = true;
}
}
return $this; // return the currenct object we are working with
}
public function action($action, $table, $where = array()) {
if(count($where) === 3) {
$operators = array('=', '>', '<', '>=', '<=');
$field = $where[0];
$operator = $where[1];
$value = $where[2];
if(in_array($operator, $operators)) {
$sql = "{$action} * FROM {$table} WHERE {$field} {$operator} ?";
if(!$this->query($sql, array($value))->error()) {
return $this;
}// to check to see if operator is inside the operators .... We do a ? so that we can bind the value on
}
}
return false;
}
public function get($table, $where){
return $this->action('SELECT *', $table, $where);
}
public function delete($table, $where) {
return $this->action('DELETE ', $table, $where);
}
public function error() {
return $this->_error;
}
public function count() {
return $this->_count;
}
}
index.php
<?php
require_once 'core/init.php';
$user = DB::getInstance()->get('users', array('username', '=', 'alex'));
if (!$user->count()) {
echo 'No user';
} else {
echo 'OK!';
}

Answer 1

Your get() method will always fail since it's generating an invalid SQL query.
Explanation
If we take your request:
$user = DB::getInstance()->get('users', array('username', '=', 'alex'));
and break it up to see what happens (this is the same thing as the above):
// This will work and return an instance of DB
$db = DB::getInstance();
// Will always fail and return false, since the get() method fails
$user = $db->get('users', array('username', '=', 'alex'));
// Since user is false (a boolean), it doesn't have any methods
$user->count()
So, why does it fail? Let's look in your DB class.
Let's start with the get() method:
public function get($table, $where){
// This is calling an internal method called "action()" passing three values
return $this->action('SELECT *', $table, $where);
}
and where it fails, the action() method:
public function action($action, $table, $where = array()) {
if(count($where) === 3) {
$operators = array('=', '>', '<', '>=', '<=');
$field = $where[0];
$operator = $where[1];
$value = $where[2];
if(in_array($operator, $operators)) {
// The get() method passed 'SELECT *' to this method, so the below string will be
// "SELECT * * FROM users WHERE username = ?"
// (hint: it's the double * * that's invalid) .
$sql = "{$action} * FROM {$table} WHERE {$field} {$operator} ?";
if(!$this->query($sql, array($value))->error()) {
// Since the query fails, it will never come here
return $this;
}
}
}
// Since the query fails (is invalid), this is what it will return
return false;
}
Solution
A quick fix would be to change the action() method from:
$sql = "{$action} * FROM {$table} WHERE {$field} {$operator} ?"
to
$sql = "{$action} FROM {$table} WHERE {$field} {$operator} ?"
As I've mentioned in comments, you should look into proper error handling for PDO. Or better yet, use some tried and tested db library.
You mentioned that you are new to PHP and are going through some tutorial, the would recommend learning the basics step by step.