Prepare multiple statments before executing them in a transaction?

Question

Is it ok to prepare multiple statments before executing them?

$db = PDO('..connection info...');
$cats_stmt = $db->prepare('SELECT * FROM cats');
$dogs_stmt = $db->prepare('SELECT * FROM dogs');

$cats_stmt->execute();
$cats = $cats_stmt->fetchAll(PDO::FETCH_CLASS);//list of cats

$dogs_stmt->execute();
$dogs = $dogs_stmt->fetchAll(PDO::FETCH_CLASS);//list of dogs

This would come in handy for loops where 2 statements with different variables need to be executed after each other. like this:

$stmt_addcat = $db->prepare('INSERT INTO cats (name,age) VALUES(?,?)');
$stmt_adddog = $db->prepare('INSERT INTO dogs (name,age) VALUES(?,?)');

foreach($cat_n_dog as $bunch){
  $db->beginTransaction();
  $dog_name = $bunch['dog']['name'];
  $dog_age  = $bunch['dog']['age'];
  $stmt_adddog->bindParam(1,$dog_name,PDO::PARAM_STR);
  $stmt_adddog->bindParam(2,$dog_age,PDO::PARAM_STR);
  $result = $stmt_adddog->execute();
  if($result===false){
    $db->rollBack();
    continue;
  }
  $cat_name = $bunch['cat']['name'];
  $cat_age  = $bunch['cat']['age'];
  $stmt_addcat->bindParam(1,$cat_name,PDO::PARAM_STR);
  $stmt_addcat->bindParam(2,$cat_age,PDO::PARAM_STR);
  $result = $stmt_addcat->execute();
  if($result===false){
    $db->rollBack();
    continue;
  }
  $db->commit();
}

I am asking because I had situations where PDO would act buggy and throw errors on the sqlite driver, so I'm wondering if the above example is even supposed to work.

p.s. examples are made-up on the spot.

Answer 1

I'll post as answer since comments don't allow enough space.

Yes, you can prepare several prepared statements and then execute them in a loop, there's nothing wrong with that.

The transaction part is wrong. If you want to execute all or no queries, you need to start your transaction outside of the loop (same with commit). That's where PHP's try/catch comes in handy.

$db = PDO('..connection info...');

$db->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION); // Set error mode to exceptions

try
{
    $stmt_addcat = $db->prepare('INSERT INTO cats (name,age) VALUES(?,?)');
    $stmt_adddog = $db->prepare('INSERT INTO dogs (name,age) VALUES(?,?)');

    $db->beginTransaction();

    foreach($cat_n_dog as $bunch) { } // Do your foreach binding and executing here 

    $db->commit();
}
catch(PDOException $e)
{
    $db->rollBack();

    echo "Error occurred. Error message: ". $e->getMessage() .". File: ". $e->getFile() .". Line: ". $e->getLine();
}