PHP数组问题 - 未定义的偏移量

Question

I have an array defined as such:

<?php $Invoices = array();
foreach ($bookings as $booking){
    $Invoices[$booking['id'] = $booking['invoice_no']];
}
?>

However, I'm getting a Notice (8): Undefined offset error.

Currently, all $booking['id'] are identical to $booking['invoice_no'] - that will change; they're just test values for now (otherwise I would just stick to using $bookings).

I plan to use the array for options in a form input:

<div class="col-sm-12">
    <?= $this->Form->input('booking_id', ['class' => 'form-control',
    'label' => 'Invoice Number', 'id' => 'booking_id', 'options' => 
    $Invoices]); ?>
</div>

Checking my CakePHP 3 debugger, $bookings definitely has sub arrays with elements - for example, $bookings[0]['id'] = $bookings[0]['invoice_no'] = 10.

Answer 1

bad syntax here: $Invoices[$booking['id'] = $booking['invoice_no']];

Should be:

$Invoices[$booking['id']] = $booking['invoice_no'];