separating connection to database and queries - php

Question

What is the proper way to "encapsulate" the sql queries scripts and connection script with try/catch or if/else blocks? I want to have a config.php file that will contain the connection part:
<?php
$servername = "localhost";
$username = "username";
$password = "password";
try {
$conn = new PDO("mysql:host=$servername;dbname=myDB", $username, $password);
// set the PDO error mode to exception
$conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
echo "Connected successfully";
}
catch(PDOException $e)
{
echo "Connection failed: " . $e->getMessage();
}
?>
Now taken from w3schools, when they insert a value to the database, they simply re-write the entire connection part again:
<?php
$servername = "localhost";
$username = "username";
$password = "password";
$dbname = "myDBPDO";
try {
$conn = new PDO("mysql:host=$servername;dbname=$dbname", $username, $password);
// set the PDO error mode to exception
$conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
$sql = "INSERT INTO MyGuests (firstname, lastname, email)
VALUES ('John', 'Doe', 'john#example.com')";
// use exec() because no results are returned
$conn->exec($sql);
echo "New record created successfully";
}
catch(PDOException $e)
{
echo $sql . "<br>" . $e->getMessage();
}
$conn = null;
?>
but I want to properly separate the two. Also, if I use prepared statements, do I need to check if on each part? i.e the prepare, bindParam and execute? Or a single try/catch or if/else is enough:
// Prepare an insert statement
$sql = "INSERT INTO table(value) VALUES (:value)";
$stmt = $conn->prepare($sql);
// Bind variables to the prepared statement as parameters
$stmt->bindParam(':value', $value, PDO::PARAM_STR);
$stmt->execute(); //does each part here need an if/else?

Answer 1

You should only make the connection once. There's no need to close and reopen the connection between queries. I assume the reason the example at w3schools is written that way is so that it will be self-contained, executable as-is without relying on a connection established in another example.
If you have the code that defines your connection in one file like the first example you showed, you can include that file in other files that need a connection to execute queries, and $conn will be available there. For a simple project, that's all you really need.
As far as if/else or try/catch, since you have set the PDO::ATTR_ERRMODE attribute on your connection to PDO::ERRMODE_EXCEPTION, then wrapping bits of code where a query may fail in if/else probably won't be that useful, because an exception will be thrown if the query fails, so handling the exception in a catch block will work better. You can examine the exception to see exactly what went wrong, log the error, and show an appropriate error message to the user where applicable. Dumping every exception message to the screen as shown in the second example is generally not a good way to show appropriate error messages to users.
You should include the prepare, bind, and execute in the try block. execute() is not the only thing that can cause an exception. prepare() may throw an exception if you aren't using emulated prepared statements (depending on the setting of PDO::ATTR_EMULATE_PREPARES), and bind can also cause an exception, for example if you mess up a named placeholder.
if/else is more useful for checking the results of queries that executed successfully (e.g. did this select statement return any records). The level of detail of error handling you need determines how many if/else, try/catch blocks you need.