29 Mar 09 Event Calendar: Time Zone Picker and Updates
I ended up creating a time zone picker for the event calendar. I saw the idea on the web somewhere. The problem is that there are nearly 400 common time zones in the database. Since every time zone is named in the format “area/location”, I created an area select and a location select. That broke up the time zones nicely, although some of the areas still have far too many entries to be completely convenient. I wrote a short Python script that parsed the pytz common time zones and generated a Javascript object literal to contain the select menus contents. Here is a screen shot showing it in action:
When you select an area (the left-most) control, the location select fills with the appropriate options. When the form is submitted, some Javascript runs to take the two select values and puts them together and populates a hidden time zone input field with the result. So, in the example above, when the form is submitted, the hidden field receives “US/Pacific”. Likewise, when the form is displayed, the hidden field is parsed and the two select controls are set accordingly. This works pretty well, although I think I could have done a better job of modularizing this code in case I need to use it in another place on the site (such as in a user’s profile). I will definitely do this later.
I’ve decided to tackle recurring events later, as it seems a bit involved, and as I stated, very few events on the calendar need this capability. So with the time zone picker in place, and the corresponding code on the server side (thanks to pytz), I can now accurately add events to the event calendar without losing local time information.
I also sat down finally and converted The Madeira’s website from mod_python to mod_wsgi. This wouldn’t have been possible without the excellent documentation that mod_wsgi has. I feel this will scale better, and it will allow me to more easily run multiple Python web applications side by side. I am anxious to get a Trac issue tracker running as well as a beta version of the new site.
The rest of the weekend was spent working the “to-do” list for the site in preparation for deploying a beta version. I really do need to get an issue tracker going to capture all the ideas and work I need to complete.
18 Mar 09 Event Calendar: Oh yeah, time zones…
Very shortly after I wrote the last blog entry I began having some nagging doubts about time zones. The current PHP version of the calendar is really time zone agnostic. It is assumed that when you see an event for California, for example, that you understand the time for the event is local to the Pacific time zone. I was kind of hoping to dodge this problem, but it seems unavoidable now that I am using Google calendar for the back-end.
The Google calendar has a time zone associated with it that I set when I created it. I am using my own local time zone: Central Standard Time, aka CST, aka GMT-6. Well, currently we are in daylight savings time (ack), so it is actually CDT, or GMT-5. When I initially added events to Google calendar, I naively just added them without providing any time zone information. Being somewhat new to Python, I haven’t totally come to grips with how Python deals with time zones, and I was just hacking with my blinders on. Well, needless to say, this didn’t work well, as Google simply assumed I was providing UTC times. Thus when they were displayed on my Google calendar, they had a nice 5 hour offset. Oops. Okay, to “fix” that, I peeked at django-cal, and noticed it was using a Django utility to provide the required time zone information. Using that technique, I got my events to show up in the correct local time on my Google calendar. Hooray!
But wait, that isn’t the whole story. Users can look at my Google calendar, and choose to copy events to their own Google calendars, which may have different time zones. Therefore, if a user submits an event to my calendar that takes place in California, my current code sets the time zone incorrectly. However this isn’t obvious as the time on my calendar will still be the same as the user entered it. But, if that user chooses to copy the event back to her California-based calendar, the event will suddenly be off by 2 hours. Crap!
So it looks like I do need to come to terms with time zones, and bite the bullet and ask the user what time zone the event is in. I am currently studying how Python handles time zones, and looking at pytz, a nice Python interface to the famous Olson database of timezones. Do I need to build some kind of time zone picker? I’m not finding a lot of those, which makes me wonder. In any event, this is seriously complicating my event calendar. But it is pretty interesting stuff and I hope I can get it right, as I really do want the events on my calendar to reflect accurate local times.
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.
08 Mar 09 Event Calendar: Submitting Events
I’m continuing on in my experiment to leverage Google calendar for my site’s event calendar. I have built a form that allows users to submit new events subject to admin approval. I modeled the form after the GUI used by Google calendar. I also decided to used jQuery UI’s datepicker. jQuery UI just released version 1.7, which is compatible with jQuery 1.3. After reading this blog entry, I’ve decided to try letting Google host jQuery for me. Google is also hosting the standard jQuery UI themes CSS files, so this seems awfully convenient.
Check out the screenshot of the event submit form:
The datepicker is very useful, and will add a lot to the site, I think. My existing PHP application is using a much less elegant form. So far this form only handles non-repeating events. I will add support for those later.
I then turned my attention to the backend: how to synchronize my event models with Google calendar? It turns out there is already a Django application designed for this purpose: django-cal. It is designed in a very generic way and seems to be very well done. I decided I didn’t need its full functionality, but I did reference the source code when designing my back end. So a big thank-you to the creators of django-cal!
At this point I have enough functionality to add events and get them on the Google calendar. I have coded, but not tested, update and delete functionality. I am using the batch facility of the gdata API. In a typical work cycle, I need to approve anywhere from 1 to 7 or so events at once. This isn’t a lot of events, but I think doing it in a batch mode will speed a synchronization cycle up noticeably.
I store a “status” field in each event that keeps track of the event status: new, new and approved, edited, edited and approved, deleted, deleted and approved, and “on calendar”. When a user adds an event it becomes “new”. An admin reviews the event, and marks it “new and approved”. After synchronization, the status changes to “on calendar”. Likewise, my plan is to let users edit and request deletes for any events that they submit. My custom admin synchronization view will the perform the operations on all events with the “… and approved” status in a batch mode.
The custom admin view I wrote about in the last entry is also working well. I overrode the base django.contrib.admin template, so it looks well-integrated with the rest of the admin part of the site. I also figured out how to use the breadcrumbs for admin navigation, and noticed the base template will display a variable called “messages” with the nice green checkmark, if present. Likewise, the admin CSS has a class called “errorlist” for displaying errors. So it is quite easy to make a pretty professional looking custom admin screen by studying the base template and admin CSS files. I will post a screenshot of my custom admin view after I get some more events through the work cycle in a future blog post.
The Python gdata API isn’t as clumsy as I first thought it was. I was able to wrap it in a Calendar class to make it easier to use. If you need to update or delete an event in batch mode, it seems like you have to retrieve the event from Google first. I struggled against this initially, since I was storing away the “edit link” for each event I create. I was hoping to use the edit link to avoid another trip to Google for an update. But after searching the Google Calendar Data API group archives, it seems that is indeed recommended to retrieve any event prior to an update or delete, at least in batch mode.
This seems to be working out well so far. After I code and test the other operations I will blog with more details.
05 Mar 09 Custom Admin View Gotcha in Django 1.1
I ran into something that took a few hours to sort out, so I thought I would write it up here in case it would help some other poor dope out.
My goal is to create a custom admin view. I noticed that the Django docs had been updated recently, documenting a new member function called get_urls() on the ModelAdmin class. The docs are kind of sketchy right now, but I gathered that this was the new way to add custom admin views for a model. However, before you can use this new feature, you have to cut over to the new scheme of hooking the contrib.admin site into your project. This is what took me a few hours to figure out, as I hadn’t noticed this change in the docs.
This is how I had my URLConf in my Django 1.0 project:
urlpatterns = patterns('',
(r'^admin/(.*)', admin.site.root),
# ...
After updating my working copy of Django trunk, this is what my URLConf needed to look like to use the new admin get_urls() scheme:
urlpatterns = patterns('',
(r'^admin/', include(admin.site.urls)),
# ...
All the changes are on line 2. Notice, there are two changes you have to make:
- The admin.site.root function is deprecated. You should now use include(admin.site.urls).
- The regular expression has changed subtly. Notice that the capturing of the part of the URL after ‘admin/’ is no longer needed. I didn’t notice this right away, and trust me, it does weird things if you leave it in.
After finally figuring these two things out, I am happy to report that the get_urls() function on my ModelAdmin class worked as I expected. For example, if I use the regular expression ‘^my_view/$’ for my custom admin view, the view will be located at /admin/appname/modelname/my_view. This isn’t quite made crystal clear in the Django docs.
Now I am poised to add a custom admin view on my Google Calendar application. Stay tuned for more on that.
