MySQLi as an static class - php

Question

I have the following code that is able to create a class that has a single static instance of the database object, and two static functions for rows and columns.
<?php class Database{
private static $instance;
private function __construct() {}
private function __clone(){}
public static function call(){
if(!isset(self::$instance)){
self::$instance = new MySQLi("localhost", "foo", "bar", "fizz");
if(self::$instance->connect_error){
throw new Exception('Error MySQL: ' . self::$instance->connect_error);
}
}
return self::$instance;
}
public static function getRow($id, $db){
$query = "SELECT * FROM ".$db." WHERE id=".$id;
$result = self::call()->query($query);
return $result->fetch_assoc();
}
} ?>
However, when I call getRow from another class, like this
$data = Database::getRow($id, "posts");
I get the following error:
Fatal error: Call to a member function
fetch_assoc() on a non-object in
database.php
on line 27
And I check it again and again and everything seems to be in order, maybe I have a error in call() ?

Answer 1

That will happen if you have an error in your SQL syntax -- did you check it and make sure there were no errors?
I would have error checking, something like
if( self::$instance->error ) {
// Handle error
}

Answer 2

You are passing in a variable called $db to getRow(), maybe that should be a table?

Answer 3

query() will return false if the SQL query fails. You can add the following to handle this error:
$result = self::call()->query($query)
if($result === false)
throw new Exception(call()->error); // throw exception, use MySQLi error as message
return $result->fetch_assoc();

Answer 4

public static function getRow($id,$table)
{
$query = "SELECT * FROM ".$table." WHERE id=".$id." LIMIT 1";
$result = $this->instance->query($query);
return $result->fetch_assoc();
}

Answer 5

this line
if(!isset(self::$instance)){
will have sometimes strange behaviours. checking isset() against a null value is subject to failings. try this:
private static $instance = null; // it defaults to null but hey, rather be on the sure side
// foo
if (self::$instance === null) {
// mysqli creation foo

Answer 6

I have tried this code and it works, you must have an error in the query. What may cause this error is:
Check what you pass to Database::getRow(). There may be some non-numerical characters in your id
Check if column name 'id' exists, this sounds funny but it happened to me a million times, i was querying column 'id' instead of 'product_id' and so on
Check if table $db exists
Make sure you don't switch the function parameters by an accident. Database::getRow(24, 'people'); instead of Database::getRow('people', 24);
I can't think of anything else that may cause this error.