PHP
Connecting with PDO
Learn to connect to a database with the PDO constructor and a DSN.
The PDO constructor
To connect to PDO write new PDO($dsn, $user, $password). The DSN is the connection string; it starts with a driver name like sqlite::memory:.
SQLite needs no user or password; the DSN alone is enough. For MySQL you write mysql:host=localhost;dbname=test and pass $user and $password arguments.
If the connection fails PHP throws a PDOException.
PDOException and error mode
If something fails while connecting (for example a wrong DSN), PDO throws a PDOException. If not caught the program stops.
Wrap the connection code in try/catch; catch with catch (PDOException $e). Set the error mode with $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION) so query errors also throw exceptions.
To close the connection write $pdo = null; PHP also closes it automatically when the script ends.
Exercise Safe connection with try/catch
Connect to in-memory SQLite with new PDO('sqlite::memory:'). Wrap the connection in try/catch; catch with catch (PDOException $e). On success print 'OK'; on error print the message with $e->getMessage().
Show example solution
:memory:'); and print with echo 'OK' . "\n";. Catch with catch (PDOException $e) and print the message with echo $e->getMessage() . "\n";.
Example solution:
<?php
// Build a safe connection with try/catch
try {
$pdo = new PDO('sqlite::memory:');
echo 'OK' . "\n";
} catch (PDOException $e) {
echo $e->getMessage() . "\n";
}
Test yourself
-
Complete the PDO constructor call
<?php
$dsn = 'sqlite::memory:';
$pdo = ____($dsn);
echo get_class($pdo) . "\n";
?>
Show answer
<?php
$dsn = 'sqlite::memory:';
$pdo = new PDO($dsn);
echo get_class($pdo) . "\n";
?>
-
What should you do when a PDOException is thrown while connecting?
- Catch it with try/catch
- Wait for the program to crash
- Exit immediately with die()
- Print a warning with echo and continue
Show answer
Catch it with try/catch — Correct. try/catch catches the PDOException; the catch block handles the error.
-
Match the connection concepts
- new PDO($dsn)
- Opens connection
- PDOException
- Connection error
- $dsn
- Connection string
- try/catch
- Catches errors
Next lesson: Running queries with query()
