php connect_errno vs checking if db == false - php

Question

I am working on on a small personal project to understand PHP and MySql. I set up a simple class to get started to make a connection to a database and wanted to verify the connection was good and was attempting to use the connect_errno property but I am not getting the results I expected. This is just test code so it may be missing some of the error/security checking that would normally be included in such code.
Please note that the code is running on a LAMP Stack with Ubuntu 16.04 and PHP Version of: PHP Version 7.0.22-0ubuntu0.16.04.1
In the code below I intentionally set the DB_PASS constant to an invalid value to test two different methods of verifying the connection.
Using the connect_errno method does not seem to work.
class Database
{
public $conn;
public $connStatus;
public function __construct()
{
echo "Hi There, I am a database! <br><br>";
$this->conn = mysqli_connect(DB_HOST, DB_USER, DB_PASS, DB_NAME);
if($this->conn->connect_errno)
{
echo "Bad Connection using connect_errno method <br/>";
}
else
{
echo "Good Connection using connect_errno method <br/>";
}
if ($this->conn == false)
{
echo "Bad Connection using db==false method <br/>";
}
else
{
echo "Good Connection using db==false method <br/>";
}
}
}
This code block indicates that the connection is good despite the incorrect DB_PASS. Return: Good Connection using connect_errno method.
if($this->conn->connect_errno)
{
echo "Bad Connection using connect_errno method <br/>";
}
else
{
echo "Good Connection using connect_errno method <br/>";
}
This code block indicates that the connection is bad, which is correct due to the incorrect DB_PASS. Return: Bad Connection using db==false method
if ($this->conn == false)
{
echo "Bad Connection using db==false method <br/>";
}
else
{
echo "Good Connection using db==false method <br/>";
}
I am fine with using the 'db==false' method of checking but I was curious about this. I have read several posts within Stack Exchange and tried some of those examples but they did not seem to work.
Example1: echoing-mysqli-connect-errno-not-working.
Example2: error on mysqli::connect_errno

Answer 1

Ok, after going back and reviewing the other posts I now understand the issue. The procedural method sets it up like this:
$this->conn = mysqli_connect(DB_HOST, DB_USER, DB_PASS, DB_NAME);
while the OOP method sets it up like this:
$this->conn = new mysqli(DB_HOST, DB_USER, DB_PASS, DB_NAME);
So I guess being relatively new to PHP and MySQL I did not really see the difference until taking a step back. Thanks for everyones help!

Answer 2

The difference is that mysqli_connect() will return either a mysqli object or a boolean false. But you can't use the -> operator on a variable that isn't an object.
$x = false;
echo $x->attrib; // fatal error, booleans can't have OO members or methods
This is one of the WTF moments in PHP. Because of its history, PHP language design is a Frankenstein's monster of object-oriented and non-object-oriented (made worse by many years of developing the language with no sensible design process).
So there are lots of functions in PHP which return either an object or a non-object. This makes it hard to write safe code, because you never know if you can use -> on the thing returned by a function, until you check what type it is.
The confusion is reduced if you use new mysqli(), because the OO operator new is guaranteed to return an object of that type, even if the connection fails because you gave an incorrect password or something.
$conn = new mysqli(...);
if ($conn->connect_errno) { // this is not a fatal error even if the connect failed
...
}