For Walker Open Field, we wanted a way to collect community submitted events and display them on our site. We have our own calendar and we discussed whether adding the events to our internal Calendar CMS was the best way, or if using an outside calendar solution was the direction to go. In the end, we decided to do both, using Google Calendar for community events and our own calendar CMS for Walker-programmed events.

The Open Field website is based on the lovely design work of Andrea Hyde, and the site is built using WordPress, which we use for this blog and a few other portions of our website. WordPress is relatively easy to template once, so it makes for quick development. WordPress also has a load of useful plug-ins and built-in features that saved us a lot of time. Here’s how we used it an put it together:

Collecting Events
To accept event ideas from community members, we used the WordPress Cforms II plugin, which makes it very easy to build otherwise complex forms and process them. You can create workflows with the submissions, but we simply have Cforms submit the form to us over email. A real person (Shaylie) reviews each of the event submissions and adds the details to…

Google Calendar
We use Google’s Calendar app to contain the calendar for the community events. When Shaylie gets the email about a new event, she reviews it, follows up on any conflicts or issues, and then manually adds it to google calendar. We toyed with the idea of using the Calendar API to create a form that would allow users to create events directly in the calendar, but decided against it for two reasons. First, it seemed overly complicated for what we thought would amount to less than 100 events. Secondly, we would still have to review every submission and it would be just as cumbersome to do it after the fact rather than beforehand.

We also use Google Calendar to process our own calendar internal calendar feed. The Walker Calendar can spit out data as XML and ICAL. We have our own proprietary XML format that can be rather complex, but the ICAL format is widely understood and Google Calendar can import it as a subscription.

Getting data out of Google Calendar
We now have two calendars in google calendar: Walker Events and Community Events. Google provides several ways to get data out of google calendar, and the one we use is the ATOM format with a collection of google name-spaced elements. The calendar API is quite robust, but there are a few things worth noting:

• You must ask for the full feed to get all the date info
• Make sure you set the time zone, both on the feed request but add it to the events when you link tot hem (using the
  ctz

  paramater)

• Asking for only
  futureevents

  and

  singleevents

  (as paramaters) makes life easier, since you don’t have to worry about complexities of figuruing out the repeating logic, which is complicated

This is our feed for Open Field Community Events.

Calendar data into WordPress
Since version 2.8, WordPress has included the most excellent SimplePie RSS/ATOM parsing library. As the name would have you believe, it is pretty simple to use. To pull the data out of the Google Calendar items with simplePie, you extend the SimplePie_Item class with some extra methods to get that gd:when data.

Combining two feeds in SimplePie is not hard. By default, SimplePie will sort them by the modified or published date, which in the Google Calendar API is the date the event was edited, not when it happens. Instead, we want to sort them by the

field. There are probably a few ways to do this, but the way that I set up was to simply loop through all the data, put it into an array with the timestamp as the key, and then sort that array by key. Here’s the code:

[php]
<?php

//include the rss/atom feed classes
include_once(ABSPATH . WPINC . ‘/feed.php’);
require_once (ABSPATH . WPINC . ‘/class-feed.php’);

// Get a SimplePie feed object from the specified feed source.
$calFeedsRss = array(
#walker events
‘http://www.google.com/calendar/feeds/95g83qt1nat5k31oqd898bj2ako1phq1%40import.calendar.google.com/public/full?orderby=starttime&ctz=America/Chicago&sortorder=a&max-results=1000&futureevents=true’,

#public events
‘http://www.google.com/calendar/feeds/walkerart.org_cptqutet6ou4odcg6n2mvk4f44%40group.calendar.google.com/public/full?orderby=starttime&ctz=America/Chicago&sortorder=a&max-results=1000&futureevents=true&singleevents=true’
);

$feed = new SimplePie();
$feed->set_item_class(‘SimplePie_Item_Extras’);
$feed->set_feed_url($calFeedsRss);
$feed->set_cache_class(‘WP_Feed_Cache’);
$feed->set_file_class(‘WP_SimplePie_File’);
$feed->set_cache_duration(apply_filters(‘wp_feed_cache_transient_lifetime’, 3600)); //cache things for an hour
$feed->init();
$feed->handle_content_type();

if ( $feed->error() )
printf (‘There was an error while connecting to Feed server, please, try again!’);

$count = 0; // hack, but we’re going to count each loop and use it as a little offset on the sort val
foreach ($feed->get_items() as $item){

if (strtolower($item->get_title()) != ‘walker open field’){
$eventType = ‘walker’;
$related = $item->get_links ( ‘related’ );
$related = $related[0];
if ( strpos($related,’walkerart.org’) === False ){
$related = $item->get_link();
// if it’s a google calendar event, make sure we set the tiem zone
$related .= "&ctz=America%2FChicago";
$eventType = ‘community’;
}

#we offset the actual starttime a little bit in case two events have the same start time, they would overwrite in t he array
$sortVal = $item->get_gcal_starttime(‘U’) + $count;
$myData = array(
‘title’ => $item->get_title(),
‘starttime’ => $item->get_gcal_starttime(‘U’),
‘endtime’ => $item->get_gcal_endtime(‘U’),

‘link’ => $related,
‘eventType’ => $eventType,
‘text’ => $item->get_content(),
‘date’ => $item->get_gcal_starttime(‘U’)
);
$cals[ $sortVal ] = $myData;
}
$count++;
}
//sort the array by keys
ksort($cals);
// $cals now contains all the event info we’ll need

?>
[/php]

Once this is done, you can simply take the

array and loop through it in your theme as needed. Parsing the google calendar feeds is not an inexpensive operation, so you may wish to use the Transients API in WordPress to cache this information.

Caveats and Issues
Overall, this approach has worked well for us. We have run into some issues where the Google Calendar ATOM feed would show events that had been deleted. Making sure to set the

and

paramaters fixed this. We also ran into some issues using the

, so we ended up manually creating occurrences for events that would have otherwise had a repeating structure.