Predicting future IDs used before saving to the DB - php

Question

I am saving a complex dataset in Laravel 4.2 and I am looking for ways to improve this.
$bits has several $bobs. A single $bob can be one of several different classes. I am trying to duplicate a singular $bit and all its associated $bobs and save all of this to the DB with as few calls as possible.
$newBit = $this->replicate();
$newBit->save();
$bobsPivotData = [];
foreach ($this->bobs as $index => $bob) {
$newBob = $bob->replicate();
$newBobs[] = $newBob->toArray();
$bobsPivotData[] = [
'bit_id' => $newBit->id,
'bob_type' => get_class($newBob),
'bob_id' => $newBob->id,
'order' => $index
];
}
// I now want to save all the $bobs kept in $newBobs[]
DB::table('bobs')->insert($newBobs);
// Saving all the pivot data in one go
DB::table('bobs_pivot')->insert($bobsPivotData);
My problem is here, that I cant access $newBob->id before I have inserted the $newBob after the loop.
I am looking for how best to reduce saves to the DB. My best guess is that if I can predict the ids that are going to be used, I can do all of this in one loop. Is there a way I can predict these ids?
Or is there a better approach?

Answer 1

You could insert the bobs first and then use the generated ids to insert the bits. This isn't a great solution in a multi-user environment as there could be new bobs inserted in the interim which could mess things up, but it could suffice for your application.
$newBit = $this->replicate();
$newBit->save();
$bobsPivotData = [];
foreach ($this->bobs as $bob) {
$newBob = $bob->replicate();
$newBobs[] = $newBob->toArray();
}
$insertId = DB::table('bobs')->insertGetId($newBobs);
$insertedBobs = DB::table('bobs')->where('id', '>=', $insertId);
foreach($insertedBobs as $index => $newBob){
$bobsPivotData[] = [
'bit_id' => $newBit->id,
'bob_type' => get_class($newBob),
'bob_id' => $newBob->id,
'order' => $index
];
}
// Saving all the pivot data in one go
DB::table('bobs_pivot')->insert($bobsPivotData);
I have not tested this, so some pseudo-code to be expected.