How to save new transients if query changes?

Question

I am using WP REST API to pull blog posts into another site. Everything works great, but now I need to save the results into transients to prevent querying the blog every time. I am new to transients and also new to WP REST api, so I am looking for the correct/best way to do this.

I have a function get_blog_posts_by_tags($tags) which uses the WP REST API to retrieve the posts. Once I have the results in a variable I set the transient. However, $tags might change from page to page where these posts are displayed. How do I go about checking if the new WP REST API query is the same/different from the one already stored in the transient?

function get_posts_by_tags($tags){
    if(false === ($result = get_transient('rest-posts'))) {
        $args = array(
            'filter[orderby]' => 'date',
            'filter[posts_per_page]' => 4,
            'filter[order]' => 'DESC',
            'filter[post_status]' => 'publish',
            'filter[tag]' => $tags,
        );
        $url = 'http://blog.myblog.com/wp-json/posts';
        $url = add_query_arg($args,$url);
        $response = wp_remote_get($url);
        //Check for error
        if (is_wp_error($response)) {
            return sprintf( 'The URL %1s could not be retrieved.', $url);
        }
        //get just the body
        $data = wp_remote_retrieve_body($response);
        //return if not an error
        if (!is_wp_error($data)){
          //decode and return
          $result = json_decode( $data );
          set_transient('rest-posts', $result,24 * HOUR_IN_SECONDS);
        }
    }
    return $result;
}

I thought about storing the WP API query into another transient and then use get_transient() every time and check if the transient content (the query wp api query) matches the new wp api query. But that seems a bit redundant and I am not sure it's the best approach.

Answer 1

According to code in OP, the only thing that changes the result is the $tags variable.

In this case, the easiste way to do the trick is make the $tags part of the transient name.

function get_posts_by_tags($tags){

    $transient = 'rest-posts-' . md5(serialize($tags));

    if(false === ($result = get_transient($transient))) {

          // the rest of yout function here ...

          if (!is_wp_error($data)){
             $result = json_decode( $data );

             set_transient($transient, $result, 24 * HOUR_IN_SECONDS);
          }   
    }

    return $result;
}

So for every $tags there is a transient.

If different pages result in same $tags they will query (and store) same transient and everything should work as expected.