15 Mar 09 Event Calendar: Everything But Repeating Events

Continuing along with the Google calendar integration, I built views to allow users to edit and delete the events they have previously submitted. These actions are simply requests; the admin still has to approve them. In the PHP version, these updates did not require admin approval. Here, they do, because the admin must supply the Google password to synchronize the events on the Google calendar. So the events simply get marked as “edit request” or “delete request”, which the admin must approve by toggling the status to “edit approved” or “delete approved”. The admin then visits the custom Google sync view, supplies the password, and the events are synchronized with Google via the gdata API. This seems to be working out well, although I’m not entirely happy with the workflow in the admin area to accomplish all this. Right now I have to visit the model change list, approve changes, then go to the custom Google sync view. We’ll see how this works out in practice.

I was very pleasantly surpised at how easy it was to add a link to my custom Google sync view in the admin area. I decided I wanted this link visible on all model views in the admin area (there is only one model right now: the event). I simply had to create this path in one of my template directories: admin/gcalendar/change_list.html (where gcalendar is the name of my application). Django will look to see if I have provided a change_list.html, and will use it in preference to the default one. And I didn’t even have to copy the whole template, I only needed to use template inheritance to override the block that provides the “object tools”. My change_list.html looks like this:

{% extends "admin/change_list.html" %}
{% block object-tools %}
{% if has_add_permission %}
<ul class="object-tools"><li><a href="add/{% if is_popup %}?_popup=1{% endif %}" class="addlink">Add {{ name }}</a></li>
<li><a href="google_sync/">Google Sync</a></li>
</ul>
{% endif %}
{% endblock %}

I just added the <li> and link to my “Google Sync” page. Here is a screen shot of my calendar event change list that shows this link in action. Check the upper right, next to the “Add” link. It was nice to see it was automatically styled to fit in with the rest of the admin.

Clicking on the link leads one to the custom admin view. Here, the list of approved events appears. The admin types in the Google password, and the view synchronizes (adds, updates, deletes) the events with Google. It might be a minor pain to enter your Google password every time, but I’d rather not hard-code or store the admin’s Google password in the database.

I think using Google calendar is going to be cool. I like the fact that people can add the events to their own calendars, invite other people, and set email or SMS text message reminders for these events. I also like that other people can embed the site calendar on their own websites or blogs to spread the word.

With that in place, all I have left to do is to support repeating events. And actually, as it stands right now, I can also handle multi-day events. This covers 99% of the events on SurfGuitar101.com already. There are only two weekly gigs on the calendar right now. I have worked on this off and on for 3 or 4 weeks now, and have replicated most of the PHP version’s functionality by leveraging Google and Django. It took me about 3 or 4 months before I had this much working when I initially developed the PHP-Nuke version.

Repeating events might be difficult, because the gdata API sort of punts on them. In order to specify a repeating event, I have to format a fairly complex string according to some iCalendar RFC. Yikes. I will now poke around and see if there are some Python libraries available that I could use for this, or perhaps it isn’t as bad as I think it is and I can do it by hand. Or perhaps I will leave repeating events for the future since they aren’t used that much. I am itching to get what I have created so far deployed so I can start beta-testing and getting feedback from users.

Tags: calendar, django, gdata, google, sg101

21 Feb 09 Event Calendar – Experiments with Google Calendar

I haven’t had a lot of time to explore implementing an event calendar with Google Calendar, but I did try a few things out. First of all, it is pretty easy to embed a Google Calendar into your website:

Google Calendar Embedded on Website

As I mentioned in the last post, I downloaded the Google Python gdata client library. I wrote a small Python script based on the provided example code. I was able to add events to my calendar from this Python script:

import gdata.calendar
import gdata.calendar.service
import gdata.service
import atom
import atom.service
import time

cal_client = gdata.calendar.service.CalendarService()
cal_client.email = 'xxx@gmail.com'
cal_client.password = 'xxx'
cal_client.source = 'Google-Calendar_Python_Sample-1.0'
cal_client.ProgrammaticLogin()

title = 'My Test Event from Python'
content = '''This is the content of the event in some fashion.
<a href="http://google.com">My Link</a>

http://surfguitar101.com.

<b>Bold</b> text.
<p>Here is a paragraph.</p>
<p>And another</p>
<ul><li>Item 1</li><li>Item 2</li></ul>
<img src="http://surfguitar101.com/modules/Forums/images/smiles/icon_cool.gif" alt="Smiley" />
'''
where = 'An undisclosed location.'
#cal_path = '/calendar/feeds/default/private/full'
cal_path = '/calendar/feeds/xxx@group.calendar.google.com/private/full'

event = gdata.calendar.CalendarEventEntry()
event.title = atom.Title(text=title)
event.content = atom.Content(text=content)
event.where.append(gdata.calendar.Where(value_string=where))

# Use current time for the start_time and have the event last 1 hour
start_time = time.strftime('%Y-%m-%dT%H:%M:%S.000Z', time.gmtime())
end_time = time.strftime('%Y-%m-%dT%H:%M:%S.000Z', time.gmtime(time.time() + 3600))
event.when.append(gdata.calendar.When(start_time=start_time, end_time=end_time))

new_event = cal_client.InsertEvent(event, cal_path)

As you can see, I was testing to see if I could insert HTML into the event, and if it would display correctly on the Google Calendar. According to my tests, it does appear you can insert simple HTML. The only thing that did not work was <img> tags. Unfortunately, if you log into your Google account, and then go to your Google Calendar and try to edit this event using the Google GUI, all HTML will be stripped. This will make it difficult to edit an existing event and will probably steer me towards keeping the user added event around in the database for future editing until that event has expired.

I have to say I am not really impressed with the Python API. It seems rather “un-Pythonic”. Why do I have to construct atom objects and assign them to the event title and content fields? The API should do this for me. Why do I have to format my own date strings? The API should accept Python datetime objects and do that for me. Pretty disappointing coming from Google.

I am starting to see a way forward here. I think I need to do the following:

• Build a view to let registered users submit events. Allow the event description to be submitted in Markdown format, but warn the user that images won’t work.
• In the admin interface, allow the admin to approve events by marking a boolean field in the database.
• Build a custom admin view that contains a form that prompts the admin for their  Google password, and batch inserts all approved events to the Google calendar.

Initially I will support only non-repeating events. I’ll go back and try to add support for repeating events in “phase 2″ once I get the above functionality working.

I was looking through the Django docs and came across a new feature in trunk that allows you to extend the set of URLs supported by a model in the admin section. This will allow me to create a custom admin view to insert the events. I think this is just a new way of doing something that was already supported, and is described in the online Django book. I’ll have to update my working copy of Django trunk and try this out.

Tags: calendar, django, gdata, google, sg101

15 Feb 09 Event Calendar – Use Google Calendar?

I wrote a pretty complex event calendar for my PHP-Nuke site. You can find it here on sourceforge. It allows users to submit events for admin approval. Once approved they appear on the calendar. The application does all the calendar logic, including the drawing of the calendar. Repeating events were added, and they are pretty hairy as well. There are some pretty massively complicated SQL queries in that code, not to mention some crazy PHP logic to figure out if repeating events belong on a particular calendar view. It is also possible to make exceptions to repeating events.

I’ve been thinking about how to port this to my new Django powered site. One day I stumbled across the Google Calendar API, and I’m thinking about leveraging this. I will let Google handle all the crazy calendar logic, as they are no doubt better at it than I am. I will still let users submit events to the admin, but this time I will use the Google API to add events to a Google Calendar. Google can do the heavy lifting for me when it comes to displaying events and handling repeating events. Am I cheating by doing this? Ha. Well there are some advantages to this idea for my end users:

• Anyone can display the site calendar on their blog or website. It won’t just be available on my site.
• Users can use the RSS feed that Google generates. It was always on the to-do list for the existing calendar to add this feature, but I never got around to it.
• If a user has a Google account of their own, they can add events from the new calendar to their own calendars.
• Google can configured to notify users by email or SMS text messages of events.

So I’ve decided to explore this approach. If it doesn’t look like it will pan out, I will fall back to a more direct port of my old PHP code.

This approach isn’t without its own challenges. I can see right now I am going to have to think carefully about how to provide authentication to the Django code to allow it to add events to one of my Google calendars. I obviously don’t want to hard code my Google login and password in the Django application.

I think I will attack this problem in phases:

1. Get a calendar to display on my site. This should be pretty easy; just use Google’s iframe code.
2. Add an event through the Python API to gain experience with it. This is prototype, throw-away code.
3. Build a front-end interface to let users create events, as was done in the PHP application.
4. Think about an interface for letting users change or edit events. This could range from just sending an email to the admin, who could make the changes using the Google interface on one end of the spectrum, all the way to letting Python code programatically making the changes.
5. Add support for repeating events.

I’ve already downloaded the Python version of the gdata library and have started reading the API docs. It looks interesting. Once I get familiar with this library, it looks like I could use it for other cool things like interfacing with YouTube and Google Docs.

Tags: calendar, django, gdata, google, sg101