Question

I have two complicated PHP objects, each of which has data in a few MySQL tables.

Sometimes, I just need to remove one object A from the database, and that takes 3 SQL statements.

Sometimes, I need to remove one object B from the database, which is takes 4 SQL statements, and which also needs to find and remove all of the object A’s that object B owns.

So inside the function delete_A(), I execute those statements inside of a transaction. Inside of the function that delete_B(), I want to run one great big transaction that covers the activities inside of delete_A(). If the whole atom of deleting a B fails, I need to restore all of its A’s in the rollback.

How do I update the definition of delete_A() to only open a new transaction if there isn’t already a bigger transaction running.

I expected to be able to do something like this, but the autocommit attribute doesn’t appear to get changed by beginTransaction()

function delete_A($a){
  global $pdo;
  $already_in_transaction = !$pdo->getAttribute(PDO::ATTR_AUTOCOMMIT);
  if(!$already_in_transaction){
    $pdo->beginTransaction();
  }

  //Delete the A

  if(!$already_in_transaction){
    $pdo->commit();
  }
}
function delete_B($b){
  global $pdo;
  $pdo->beginTransaction();
  foreach($list_of_As as $a){
    delete_A($a);
  }
  $pdo->commit();
}

Answer 1

I ended up just using the exception thrown by ->beginTransaction() to figure out whether I was in a transaction, and using that to decide whether to commit in the inner loop. So delete_A() ended up looking like:

function delete_A($a){
  global $pdo;
  try {
    $pdo->beginTransaction();
  } catch (PDOException $e) {
    $already_in_transaction = true;
  }

  //Delete the A

  if(!$already_in_transaction){
    $pdo->commit();
  }
}

And delete_B() works without modification.