Bulk Update Multiple Records with Separate Data — Laravel

As a rule of thumb, we should never run database queries inside a for-loop!

“Database transaction” is an expensive operation.

For example, let’s say we designed an inventory software and it’s being used in production for a year, and reached 1,000,000 transactions.

Suddenly, we learnt that we didn’t add the VAT to our transactions. For the transactions in the future, it’s pretty easy to deal with, maybe with a mutator.

class Transaction extends Model { 
    public $vat = 0.20;

    public function setPriceAttribute($value) {
        $this->attributes['price'] += $value * $this->vat;
    }
}

Future records are pretty easy to deal with. However how are we going to edit the 1 million records from the past.

For editing data from the past, I prefer to create a Seeder.

php artisan make:seeder AddVatToTransactions

How not to do it?

class AddVatToTransactions extends Seeder {

  public function run() 
  {
    $vat = 0.20;
    $transactions = Transaction::get();

    foreach ($transactions as $transaction) {
       $transaction->price += $transaction->price * $vat
       $transaction->save();
    }
  }
}

However, running it in a loop of 1 million and making a “database transaction” in each iteration of the loop — not a good idea! (Spoiler Alert: It’ll freeze your system 😀)

Then, how to do it?

Again, in our AddVatToTransactions Seeder:

The idea in mysql query is “CASE Statements”

UPDATE db.transactions
SET PRICE = CASE  
              WHEN id = 3 THEN 500
              WHEN id = 4 THEN 300
           END 
WHERE ID IN (3, 4)

Now, let’s do it in Laravel:

$vat = 0.20;
$transactions = Transaction::get();

$cases = [];
$ids = [];
$params = [];

foreach ($transactions as $transaction) {
    $cases[] = "WHEN {$transaction->id} then ?";
    $params[] = $transaction->profit * $vat;
    $ids[] = $transaction->id;
}

$ids = implode(',', $ids);
$cases = implode(' ', $cases);

if (!empty($ids)) {
    \DB::update("UPDATE transactions SET `price` = CASE `id` {$cases} END WHERE `id` in ({$ids})", $params);
}

This will make one database transaction to write it all your updates.⚡️

🗣 I can hear some of you saying: “It’s still FREEZING”

So.. Optimizing it even further:

#1: “Select” only the data you need from the database to consume less RAM.

In our example, we only use “id” and “price” columns. So let’s only select them.

$transactions = Transaction::select('id', 'price')->get();

#2: “Chunk” your collection to separate your transaction to multiple database transactions.

In Laravel, you can chunk collections like

Transaction::get()->chunk(5000);

Let’s apply all in our example

Here, first we divide our $transactions collection into 5000 chunks and we do a “database transaction” per 5k records at once.

$vat = 0.20;
$transactions = Transaction::get();

foreach ($transactions->chunk(5000) as $chunk) {
   $cases = [];
   $ids = [];
   $params = [];

   foreach ($chunk as $transaction) {
       $cases[] = "WHEN {$transaction->id} then ?";
       $params[] = $transaction->profit * $vat;
       $ids[] = $transaction->id;
   }

   $ids = implode(',', $ids);
   $cases = implode(' ', $cases);

   if (!empty($ids)) {
       \DB::update("UPDATE transactions SET `price` = CASE `id` {$cases} END WHERE `id` in ({$ids})", $params);
   }
}