PHP and MySQL Nested database connection - php

Question

This is a general example.
The application has 3 files.
conn.inc.php -- setting up the database connection
<?php
$db_host = "localhost";
$db_username = "root";
$db_pass = "";
$db_name = "hmt";
$conn = new mysqli($db_host, $db_username, $db_pass, $db_name);
if ($conn->connect_error) {
die("Connection failed: " . $conn->connect_error);
}
?>
func.inc.php -- file including functions
<?php
function load_module($module_name){
$sqlCmd = "SELECT content FROM modules WHERE name='$module_name' LIMIT 1";
$result = $conn->query($sqlCmd);
if ($result->num_rows > 0) {
while($row = $result->fetch_assoc()) {
$module_footer = $row["content"];
}
}else {
echo 'Error while loading module '.$module_name;
}
return $result;
$result->free_result();
}
?>
index.php -- the main page to display content
<?php
include 'conn.inc.php';
include 'func.inc.php';
if (!isset($_GET['page_name'])) { // if page_name is not set then reset it to the homepage
$page_name = 'module_footer';
}else{
$page_name = $_GET['module_footer'];
}
$module_content = load_module($page_name);
echo $module_content;
?>
Now my goal was to include functions inside the func.inc.php file and database into conn.inc.php, so as to keep separate and easier to read in the future.
My problem now is that the $conn variable declared in conn.inc.php cannot be used inside the function and it can't get my head around how to use it. I even tried using GLOBALS with no success.
The error for the files is this:
Notice: Undefined variable: conn in ./func.inc.php on line 4
Fatal error: Call to a member function query() on a non-object in ./func.inc.php on line 4
Which (I assume) is because the $conn variable is not in a global scope.
Now my question is. How can I keep the nested files but have the functions working? Is there a mistake in my approach or is it not possible to use a nested call to a mysql object?

Answer 1

Eventually you'll want to get into object-oriented coding but for now lets make what you have a little prettier.
When including files, you'll want to avoid things like global variables. They sound great, but end up being a pain when handling scope. So instead include a set of functions to call.
conn.inc.php
function getConnection(){
$db_host = "localhost";
$db_username = "root";
$db_pass = "";
$db_name = "hmt";
$conn = new mysqli($db_host, $db_username, $db_pass, $db_name);
if ($conn->connect_error) {
die("Connection failed: " . $conn->connect_error);
}
return $conn;
}
Then function.inc.php
<?php
function load_module($module_name){
$sqlCmd = "SELECT content FROM modules WHERE name='$module_name' LIMIT 1";
//Here is where we get our database connection.
$conn = getConnection();
$result = $conn->query($sqlCmd);
if ($result->num_rows > 0) {
while($row = $result->fetch_assoc()) {
$module_footer = $row["content"];
}
}else {
echo 'Error while loading module '.$module_name;
}
return $result;
$result->free_result();
}
And finally finish up with your index page the way it is. So now, any page that wants a database connection will need to include the conn.inc.php and simply call getConnection() to get a mysqli connection object.
Think of your program as being a series of individual functions working together. And eventually you'll get to it being a series of objects working together. Nothing should be just floating off in global space. Try to encapsulate everything in some sort of function or object to be called over and over with consistent results.

Answer 2

You'd have to do something like this:
$conn = '';
function connect() {
global $conn;
... do db stuff
}
But this is usually bad practice. A more common method is to use a singleton object to "carry" your db handle, and you new that singleton everywhere you need to do DB operations.
function do_something() {
$conn = new DBSingleton();
... do db stuff
}