缓存API调用

Question

我有以下代码来调用和回应来自站点的一些API调用。

function popular_uploads() {

// If no saved data exists in the cache
if ($json_data === false) {

    // Fetch new data from remote URL
    $gameid = $instance['code1'];
    $url = ("http://thegamesdb.net/api/GetGame.php?id=".$gameid."");
    $json = file_get_contents($url);
    $json_data = json_decode($json, false);


set_transient('my_unique_identifier', $json_data, 3600); $json_data = get_transient('my_unique_identifier');
}      

foreach ( $json_data->items as $item ) {
    $title=$item->Game->GameTitle;          
    $boxartw=$item->Game->Images->boxart[0];
    $boxart=$item->Game->Images->boxart[1];
    if ($boxart == NULL) {
    $boxart = $boxartw;}
    $publisher=$item->Game->Publisher;
    $releasedate=$item->Game->ReleaseDate;
    $newdate = date("d/m/Y", strtotime($releasedate));
    $newday = date("d", strtotime($releasedate));   
    $newmon = date("m", strtotime($releasedate));   
    $newyear = date("Y", strtotime($releasedate));      
    echo '<div class="upcoming_games_side">';
    echo '<div class="upcomig_bg"style="background-image:url(http://thegamesdb.net/banners/_gameviewcache/' .$boxart. ');></div>';
    echo '<div class="dark-screen-uc"></div>';
    echo '<img class="game-boxart_uc" alt="" src="http://thegamesdb.net/banners/_gameviewcache/'.$boxart.'"/>';
    if ($title == null){
    echo "N/A"; }else{
    echo '<h1 class="title_uc">'.$title.'</h1>';}
    if ($publisher == null){
        echo "N/A"; }else{
        echo '<p class="pub_uc">'.$publisher.'</p>';
    }
    if ($newdate == "01-01-1970"){ 
        echo "N/A";
    }else{
        echo '<date class="date_uc">'.$newdate.'</date>';
    }
    $target = mktime(0, 0, 0, $newday, $newmon, $newyear) ;
    $today = time () ;
    $difference =($target-$today) ;
    $days =(int) ($difference/86400) ;

    if ($days == "0"){ 
        echo "N/A"; }else{
        echo '<date class="count_uc">'.$days.'</date>';}
        echo '</div>';
    }
}   

但它没有工作，也没有缓存API数据。那么我的错误在哪里，并且我的代码的部分内容是错误的？我很感激任何帮助。

顺便说一下，它是一个Wordpress插件。