Namespaces and Core PHP Classes
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Let's close all our tabs and open up Container. In the last course, we created
two different ways to load Ship objects: one that reads a JSON file - JsonFileShipStorage
and another that reads from a database - PdoShipStorage:
| // ... lines 1 - 4 | |
| class Container | |
| { | |
| // ... lines 7 - 51 | |
| public function getShipStorage() | |
| { | |
| if ($this->shipStorage === null) { | |
| //$this->shipStorage = new PdoShipStorage($this->getPDO()); | |
| $this->shipStorage = new JsonFileShipStorage(__DIR__.'/../../resources/ships.json'); | |
| } | |
| // ... lines 58 - 59 | |
| } | |
| // ... lines 61 - 72 | |
| } |
And you could switch back and forth between these without breaking anything, thanks
to our cool ShipStorageInterface. Change it to use the PDO version and refresh.
Woh, new error:
Class
Service\PDOnot found inContainer.phpon line 28.
Let's check that out:
| // ... lines 1 - 4 | |
| class Container | |
| { | |
| // ... lines 7 - 24 | |
| public function getPDO() | |
| { | |
| if ($this->pdo === null) { | |
| $this->pdo = new PDO( | |
| // ... lines 29 - 31 | |
| ); | |
| $this->pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION); | |
| } | |
| // ... lines 36 - 37 | |
| } | |
| // ... lines 39 - 72 | |
| } |
use Statements for core PHP Classes?
Here, we see the exact same error as before: "Undefined Class PDO". So far, the
answer to this has always been:
Oh, I must have forgotten a
usestatement. I referenced a class, so I probably need to add ausestatement for it.
But here's the kicker: PDO is a core PHP class that happens to not live in
a namespace. In other words, it's like a file that lives at the root of you file
system: not in any directory.
So when PHP sees PDO mentioned, it looks at the top of the class for a use statement
that ends in PDO, it doesn't find one, and it assumes that PDO lives in the Service
namespace. But in fact, PDO lives at the root namespace.
The fix is easy: add a \ at the front of PDO:
| // ... lines 1 - 4 | |
| class Container | |
| { | |
| // ... lines 7 - 24 | |
| public function getPDO() | |
| { | |
| if ($this->pdo === null) { | |
| $this->pdo = new \PDO( | |
| // ... lines 29 - 31 | |
| ); | |
| $this->pdo->setAttribute(\PDO::ATTR_ERRMODE, \PDO::ERRMODE_EXCEPTION); | |
| } | |
| // ... lines 36 - 37 | |
| } | |
| // ... lines 39 - 72 | |
| } |
This makes sense: if you think of namespaces like a directory structure, This is like
saying ls /PDO . It doesn't matter what directory, or namespace, we're in, adding
the \ tells PHP that this class lives at the root namespace. Update the other places
where we reference this class.
The Opening Slash is Portable
This is true for all core PHP classes: none of them live in namespaces. So, always
include that beginning \. Now, technically, if you were inside of a file that did
not have a namespace - like index.php - then you don't need the opening \.
But it's always safe to say new \PDO: it'll work in all files, regardless
of whether or not they have a namespace.
When Type-Hints Fail
If you refresh now, you'll see another error that's caused by this same problem. But this one is less clear:
Argument 1 passed to
PDOShipStorage::__construct()must be an instance ofService\PDO, instance ofPDOgiven.
This should jump out at you: "Instance of Service\PDO". PHP thinks that argument
1 to PDOShipStorage should be this, nonsense class. There is no class Service\PDO!
Check out PDOShipStorage: the __construct() argument is type-hinted with PDO:
| // ... lines 1 - 4 | |
| class PdoShipStorage implements ShipStorageInterface | |
| { | |
| // ... lines 7 - 8 | |
| public function __construct(PDO $pdo) | |
| { | |
| // ... line 11 | |
| } | |
| public function fetchAllShipsData() | |
| { | |
| // ... lines 16 - 18 | |
| return $statement->fetchAll(PDO::FETCH_ASSOC); | |
| } | |
| public function fetchSingleShipData($id) | |
| { | |
| // ... lines 24 - 25 | |
| $shipArray = $statement->fetch(PDO::FETCH_ASSOC); | |
| // ... lines 27 - 32 | |
| } | |
| } |
But of course, this looks like Service\PDO to PHP, and that causes problems.
Add the \ there as well:
| // ... lines 1 - 4 | |
| class PdoShipStorage implements ShipStorageInterface | |
| { | |
| // ... lines 7 - 8 | |
| public function __construct(\PDO $pdo) | |
| { | |
| // ... line 11 | |
| } | |
| // ... lines 13 - 33 | |
| } |
Phew! We spent time on these because these are the mistakes and errors that we all
make when starting with namespaces. They're annoying, unless you can debug them quickly.
If you're ever not sure about a "Class Not Found" error, the problem is almost always
a missing use statement.
Update the other spots that reference PDO:
| // ... lines 1 - 4 | |
| class PdoShipStorage implements ShipStorageInterface | |
| { | |
| // ... lines 7 - 13 | |
| public function fetchAllShipsData() | |
| { | |
| // ... lines 16 - 18 | |
| return $statement->fetchAll(\PDO::FETCH_ASSOC); | |
| } | |
| public function fetchSingleShipData($id) | |
| { | |
| // ... lines 24 - 25 | |
| $shipArray = $statement->fetch(\PDO::FETCH_ASSOC); | |
| // ... lines 27 - 32 | |
| } | |
| } |
Finally, refresh! Life is good. You just saw the ugliest parts of namespaces.
Loving the course so far, but could we just add a 'use \PDO;' to the top of the file instead of prefixing each instance of PDO with a leading '\'? That way if we ever wanted to override the PDO class we would only have to update the use statement instead of find and replace all references to PDO throughout the container service?