Why do I have to assign the value of the prepare method to a variable and only then instantiate execute? in Pdo

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Ex:

$stmt = $db->prepare("SELECT * FROM BD");
$stmt->execute();

Why doesn’t it work if I instantiate the execute method from the same instance? since the value has already been passed to the prepare method? eg:

$db->prepare("SELECT * FROM DB");
$db->execute();
php pdo

2 answers

4


The $db which is your class variable PDO has the method prepare, who is responsible for preparing an execution command (SQL) and that the same returns a Pdostatement and in it has the method execute, ie, $db does not have this method execute but, it has a method that returns a Pdostatement who has the run.

In the $db you can directly use the PDO::query, that also return a Pdostatement already executed being the one with data return and PDO::exec, which executes Insert, Update and Delete commands that return the amount of affected lines.

//select
$db->query("SELECT * FROM BD");

//insert, update e delete
$rowsafetados = $db->exec("INSERT INTO BD ...");

'Cause this is all happening?

There is separation of responsibility between classes (POO) and each class has its own responsibility, $db connection and fast methods, and Pdostatement using the $db as a connection to your methods.

  • optionally it can chain calls $result = $db->prepare("SELECT * FROM BD")->execute();

  • will even work, but, the problem that ai will not be returned a Pdostatement, it will return a bool as described on the PHP.net website (http://www.php.net/manual/en/pdostatement.execute.php), maybe for some cases it works well but it is best to use a Pdostatement

  • you’re right, it should be fetch or fetchAll.

2

Because $db is an instance of the class PDO and it represents a connection with the database. Already $stmt in turn is an instance of the class PDOStatement, which in simple terms represents a single query.

Just think about it: $db can’t be executed because it is a connection, running a connection would be the act of connecting, but you are already connected. So $stmt represents a query, and it’s her you executes.

Still the class PDO has a function PDO::exec that allows you to perform queries quickly, but without the possibility to search for results, having as return only the amount of modified lines.

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