Can I include one pdo connection - php

Question

Im a just moving to using PDO for my development and I see in most tutorials that the connection is opend for each db query like in Jeffery Ways example below
$id = 5;
try {
$conn = new PDO('mysql:host=localhost;dbname=myDatabase', $username, $password);
$conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
$stmt = $conn->prepare('SELECT * FROM myTable WHERE id = :id');
$stmt->execute(array('id' => $id));
while($row = $stmt->fetch()) {
print_r($row);
}
} catch(PDOException $e) {
echo 'ERROR: ' . $e->getMessage();
}
Can I still do a connection in an external file and include it at the top of my page like with previous procedural coding and then do my queries below in the page?
<?php include 'includes/db.php';?>

Answer 1

You probably misunderstood what he says. To open one connection and use it throughout the whole application is not that something you "can" but actually you should.
So - yes, you are doing it right.
Also note that this thing with
try {
...
} catch(PDOException $e) {
echo 'ERROR: ' . $e->getMessage();
}
that Jeffery taught you is wrong. Never use a try catch to echo an error message. PHP will handle it better
So, your code should be like this
include 'includes/db.php';
$stmt = $pdo->prepare('SELECT * FROM myTable WHERE id = :id');
$stmt->execute(array('id' => $id));
while($row = $stmt->fetch()) {
print_r($row);
}
while db.php has to contain something like this
<?php
$dsn = "mysql:host=localhost;dbname=test;charset=utf8mb4";
$opt = array(
PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION,
PDO::ATTR_DEFAULT_FETCH_MODE => PDO::FETCH_ASSOC
);
$pdo = new PDO($dsn, $username, $password, $opt);
Also note that when using this PDO object, you have to be aware of the variable scope.
Further reading: https://phpdelusions.net/pdo

Answer 2

The short answer is yes,
if you are farmilier with OOPHP it might be worth creating a wrapper class to help with running queries but just creating the connection in a file and including it will get the job done
in the above example you can put
try {
$conn = new PDO('mysql:host=localhost;dbname=myDatabase', $username, $password);
$conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
}
} catch(PDOException $e) {
echo 'ERROR: ' . $e->getMessage();
}
into your db.php and the run the queries
$stmt = $conn->prepare('SELECT * FROM myTable WHERE id = :id');
$stmt->execute(array('id' => $id));
wherever you need.
it may also be worth mentioning that you dont have to use prepared statements with PDO which can speed things up in coding however if you wish to do that i would highly recomend a database wrapper class
non prepared statement
<?php
try {
$conn = new PDO('mysql:host=localhost;dbname=myDatabase', $username, $password);
$conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
}
} catch(PDOException $e) {
echo 'ERROR: ' . $e->getMessage();
}
$query = "
SELECT
col_1,
col_2
FROM
table_1
WHERE
col_3 = " . $conn->quote($_POST['input']); //the quotr is important, it escapes dangerous characters to prevent SQL injection
//this will run the query for an insert this is all thats needed
$statement = $conn->query($query);
//fetch single col
$col = $statement->fetch(PDO::FETCH_ASSOC);
//fetch all collums
$cols = $statement->fetchAll(PDO::FETCH_ASSOC);
the advantage of this way is that you can build up the query SQL in a more simple to follow manner, i should not that i havent tested this code but in theory it should be fine as this is how i do database handling
Edit:
Your Common Sense brings up a good point about the echo 'ERROR: ' . $e->getMessage(); being a bad idea and this is a prime example of why you should NEVER blindly copy and paste code

Answer 3

Yes, example:
db.php
<?php
$dsn = 'mysql:dbname=testdb;host=127.0.0.1';
$user = 'dbuser';
$password = 'dbpass';
try {
$dbh = new PDO($dsn, $user, $password);
$dbh->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
} catch (PDOException $e) {
echo 'Connection failed: ' . $e->getMessage();
}
?>
FROM:
http://www.php.net/manual/en/pdo.error-handling.php
Then just include db.php. I name my connection $PDO, seems more implicit, especially when you are building a prepared statement on that.