I am new to coding with php and using the Google Books API. Since there is a 1000 request limit per day for the Google Books API, I am just making sure my code is not clunky before I enabling billing. Below is how I am currently getting the book cover image to display with my WordPress posts:
<?php
$url = get_post_meta($post->ID, 'URL', true);
if($url != '') { echo "<a href='$url' target='_blank'>"; } ?>
<div class="book-cover">
<?php
$isbn = get_post_meta($post->ID, 'ISBN', true);
$page = file_get_contents("https://www.googleapis.com/books/v1/volumes?q=isbn:$isbn&key=xxxx");
$data = json_decode($page, true);
$cover = $data['items'][0]['volumeInfo']['imageLinks']['thumbnail'];
echo "<img src='$cover' />"; ?>
</div><?php if($url != '') { echo "</a>"; }
?>
Thank you very much for any assistance!