Laravel attach pivot to table with multiple values

From version 5.1 of Laravel (Currently in Laravel 9.x) onwards it is possible to pass an array as a second argument with all the additional parameters that need to be saved in the intermediate table. As you can read in the documentation

When attaching a relationship to a model, you may also pass an array of additional data to be inserted into the intermediate table:

$user->roles()->attach($roleId, ['expires' => $expires]);

For convenience, attach and detach also accept arrays of IDs as input:

$user->roles()->attach([1 => ['expires' => $expires], 2, 3]);

Then you can simply do

$food->allergies()->attach([1 => ['severity' => 3], 4 => ['severity' => 1]]);

You can.

From this example in Docs (4.2, 5.0):

$user->roles()->sync(array(1 => array('expires' => true)));

Hardcoded version for the first two rows:

$food = Food::find(1);
$food->allergies()->sync([1 => ['severity' => 3], 4 => ['severity' => 1]]);

Dynamically, with your arrays $allergy_ids and $severities in a compatible state (size and sort), you shall prepare your sync data before. Something like:

$sync_data = [];
for($i = 0; $i < count($allergy_ids); $i++))
    $sync_data[$allergy_ids[$i]] = ['severity' => $severities[$i]];

$food->allergies()->sync($sync_data);

You can't do it like you' like so I suggest a simple loop:

foreach ($allergy_ids as $key => $id)
{
  $food->allergies()->attach($id, array_get($severity_ids, $key));
  // should you need a sensible default pass it as a 3rd parameter to the array_get()
}

workaround However if you wanted to attach multiple allergies with single severity level/id then you could do this:

$food->allergies()->attach($allergy_ids, array('severity' => $singleSeverityValue));