wordpress - JSON FORMAT で Woocommerce から注文をエクスポートする

Question

wordpress Woocommerceのプラグインから注文項目をエクスポートしようとしています。配列内の注文のデータを取得するためのクエリを使用して、wordpress でテンプレートを作成します。

<?php 
//query
      global $woocommerce; 
        global $wpdb; 
        global $product;
      $args = array(
        'post_type'     => 'shop_order',
            'orderby' => 'ID',
        'post_status'     => 'publish',
            'posts_per_page' => -1,
        'tax_query' => array(array(
                            'taxonomy' => 'shop_order_status',
                            'field' => 'slug',
                            'terms' => array('processing'))));
      $loop = new WP_Query( $args );
      $order_id = $loop->post->ID;
      $order = new WC_Order($order_id); 
        $product = new WC_Product($order_id);

  //Email verificacion if is suscribed or not
  $sql = "SELECT * FROM dsr_wysija_user WHERE email='". $order->order_custom_fields['_billing_email'][0] ."'" ;
  $res = mysql_query($sql);
  if (mysql_num_rows($res)== 1){
  $email = 'true';
  }else{
    $email = 'false';
}
// Getting names of categories and quantity 
foreach($order->get_items() as $item) 
{
   $item['name']; 
   $item['qty'];
}


//Collecting data in ARRAY
  $json[]= array(
        "salutation"=>''. $order->order_custom_fields['_billing_titel'][0] .'' ,
        "title"=>''. $order->order_custom_fields['_billing_anrede'][0] .'',
        "first_name"=>''. $order->order_custom_fields['_billing_first_name'][0] .'',
        "last_name"=>''. $order->order_custom_fields['_billing_last_name'][0] .'',
        "street"=>''. $order->order_custom_fields['_billing_address_1'][0] .'',
        "street_number"=>''.$order->order_custom_fields['_billing_address_2'][0] .'',
        "address_supplement"=>''. $order->order_custom_fields['_billing_company'][0] .'',
        "zipcode"=>''. $order->order_custom_fields['_billing_postcode'][0] .'',
        "city"=>''. $order->order_custom_fields['_billing_city'][0] .'',
        "country"=>''. $order->order_custom_fields['_billing_country'][0] .'',
        "terms_accepted"=>'true',
        "receiving_mails_accepted"=>''.$email.'',   
        "email"=>''. $order->order_custom_fields['_billing_email'][0] .'',
        "original_created_at"=>''.$order->order_date.'', );


  //Starting While
  while ( $loop->have_posts() ) : $loop->the_post();
  //Printing Output array
  // echo (json_format($json))
?>


<?php endwhile; ?>

出来上がりはこんな感じ

{
  "salutation": "Arq.",
  "title": "herr",
  "first_name": "Ted",
  "last_name": "Mosby",
  "street": "Manhattan",
  "street_number": "20",
  "address_supplement": "How I met your mother",
  "zipcode": "MANHATTAN",
  "city": "New York",
  "country": "ES",
  "terms_accepted": "true",
  "receiving_mails_accepted": "true",
  "email": "ted@mosby.com",
  "original_created_at": "2014-01-07 03:34:31"
}     

しかし、私が必要なのは

{
  "salutation": "Arq.",
  "title": "herr",
  "first_name": "Ted",
  "last_name": "Mosby",
  "street": "Manhattan",
  "street_number": "20",
  "address_supplement": "How I met your mother",
  "zipcode": "MANHATTAN",
  "city": "New York",
  "country": "ES",
  "terms_accepted": "true",
  "receiving_mails_accepted": "true",
  "email": "ted@mosby.com",
  "original_created_at": "2014-01-07 03:34:31"
  "items": [
    {
      "campaign_number": 301,
      "item_number": 1
    },
    {
      "campaign_number": 301,
      "item_number": 2
    },
    ...
  ]
},
...
]
}