[php] Eloquent: find() and where() usage laravel

I am trying to get a record from a posts database table using its id. I've been banging my head on the find() method for quite sometime now, confused as to why it wasn't working. Here is my query that looks correct to me but didn't work:

$post = Post::find($id);
$post->delete();

Reluctantly i did this:

$post = Post::where('id', $id);
$post->delete();

and surprisingly enough, it worked but I have no idea how.

I also know that unlike find(), where() is a query builder and so I could also use it like this: Post::where('id', $id)->first()

Any ideas about the difference in the way the methods work?

To add to craig_h's comment above (I currently don't have enough rep to add this as a comment to his answer, sorry), if your primary key is not an integer, you'll also want to tell your model what data type it is, by setting keyType at the top of the model definition.

public $keyType = 'string'

Eloquent understands any of the types defined in the castAttribute() function, which as of Laravel 5.4 are: int, float, string, bool, object, array, collection, date and timestamp.

This will ensure that your primary key is correctly cast into the equivalent PHP data type.

Not Found Exceptions

Sometimes you may wish to throw an exception if a model is not found. This is particularly useful in routes or controllers. The findOrFail and firstOrFail methods will retrieve the first result of the query. However, if no result is found, a Illuminate\Database\Eloquent\ModelNotFoundException will be thrown:

$model = App\Flight::findOrFail(1);

$model = App\Flight::where('legs', '>', 100)->firstOrFail();

If the exception is not caught, a 404 HTTP response is automatically sent back to the user. It is not necessary to write explicit checks to return 404 responses when using these methods:

Route::get('/api/flights/{id}', function ($id) {
    return App\Flight::findOrFail($id);
});