Inline admin forms with admin site links in Django

I have a somewhat difficult relationship with Django's admin site. It's a very useful feature, but I haven't really done enough with it to know when I'm going to hit a wall, if that wall's in the code or in my understanding, and how hard it's going to be to climb over the wall.

This time I wanted to have inline admin forms, except that I didn't actually want to have the forms there, I just wanted to have links to the objects — and not their views on the actual site, but on the admin site. As far as I can tell, there's no built-in support for this.

According to the admin docs, there are two subclasses of InlineModelAdmin: TabularInline and StackedInline. Looking at django/contrib/admin/options.py confirms this. And as the docs say, the only difference is the template they use. The stacked version comes pretty close when we add all the fields to an InlineModelAdmin subclass's exclude array, but it doesn't have the link.

To solve this we first create a new subclass:

class LinkedInline(admin.options.InlineModelAdmin):
    template = "admin/edit_inline/linked.html"

When you want to create inline links to a model, you subclass this new LinkedInline class. So to use a slightly contrived example, if we have a Flight with Passengers:

class PassengerInline(LinkedInline):
    model = models.Passenger
    extra = 0
    exclude = [ "name", "sex" ] # etc

class FlightAdmin(admin.ModelAdmin):
    inlines = [ PassengerInline ]

And yes, we have to exclude all the fields explicitly: an empty fields tuple or list is ignored.

The new template is easiest to create by cutting down aggressively the stacked template. Like this:

{% load i18n %}
<div class="inline-group">
  <h2>{{ inline_admin_formset.opts.verbose_name_plural|title}}</h2>
{{ inline_admin_formset.formset.management_form }}
{{ inline_admin_formset.formset.non_form_errors }}

{% for inline_admin_form in inline_admin_formset %}
<div class="inline-related {% if forloop.last %}last-related{% endif %}">
  <h3><b>{{ inline_admin_formset.opts.verbose_name|title }}:</b>&nbsp;{% if inline_admin_form.original %}{{ inline_admin_form.original }}{% else %} #{{ forloop.counter }}{% endif %}
    {% if inline_admin_formset.formset.can_delete and inline_admin_form.original %}<span class="delete">{{ inline_admin_form.deletion_field.field }} {{ inline_admin_form.deletion_field.label_tag }}</span>{% endif %}
  </h3>
  {{ inline_admin_form.pk_field.field }}
  {{ inline_admin_form.fk_field.field }}
</div>
{% endfor %}
</div>

The primary/foreign key fields are necessary to keep Django happy.

The result looks about right, it just lacks the links. It seems that Django doesn't give the template all the information we need to make them work: there's root_path that gives us /admin/, app_label contains the application's name and inline_admin_form.original.id contains the id of the inline object. What is lacking is the path component that names the model. I don't think it's available by default (is there a clean way to ask Django what's available in a template's context?), so we need to add it. Amend LinkedInline to look like this:

class LinkedInline(admin.options.InlineModelAdmin):
    template = "admin/edit_inline/linked.html"
    admin_model_path = None

    def __init__(self, *args):
        super(LinkedInline, self).__init__(*args)
        if self.admin_model_path is None:
            self.admin_model_path = self.model.__name__.lower()

Now inline_admin_formset.opts.admin_model_path will be bound to the lowercase name of the inline object's model, which is what the admin site uses in its paths.

With this, we can now replace the inline-related div in the template with this:

<div class="inline-related {% if forloop.last %}last-related{%  endif %}">
  <h3><b>{{ inline_admin_formset.opts.verbose_name|title  }}:</b>&nbsp;<a href="{{ root_path }}{{ app_label }}/{{ inline_admin_formset.opts.admin_model_path }}/{{ inline_admin_form.original.id }}/">{% if inline_admin_form.original %}{{ inline_admin_form.original }}{% else %} #{{ forloop.counter }}{% endif %}</a>
    {% if inline_admin_formset.formset.can_delete and inline_admin_form.original %}<span class="delete">{{ inline_admin_form.deletion_field.field }} {{ inline_admin_form.deletion_field.label_tag }}</span>{% endif %}
  </h3>
  {{ inline_admin_form.pk_field.field }}
  {{ inline_admin_form.fk_field.field }}
</div>

That's it. Now Flights get links to Passengers without big forms cluttering up the page.

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iPhone shuffle

These days I use an iPhone as my mobile music device. I have a bit over 1800 songs on it. I usually use shuffle and had it stuck in a weird state a couple of weeks ago — it was constantly playing me just a few tracks. I usually listen for just half an hour to an hour at a time, so I don't know if it would have started looping or what, but those were basically always there for a week's worth of commutes. I finally restarted the phone and that seemed to help, but what do you know, a couple of weeks, several restarts and one operating system upgrade later, it's again playing me exactly the same tracks.

As much as I love the The Roots, honestly, at this points Adrenaline!'s "Once a-again, once a-gain..." start makes me mostly think "once again indeed."

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Crashes with NSURLConnection

Speaking of Cocoa (and iPhone) programming, for a change.

Having trouble with spurious EXC_BAD_ACCESS crashes when using NSURLConnection? NSZombie giving you not very clear messages about [Not A Type retain], pointing to an address that malloc_history says has been allocated somewhere with only framework code in the call stack? See Amro Mousa's blog entry about the subject.

In a nutshell, don't send the start message to a NSURLConnection object you've initialized with a +connectionWithRequest:delegate: or -initWithRequest:delegate:. It'll break stuff.

Apple, how about a warning about this in the docs? The docs for -start say "Causes the receiver to begin loading data, if it has not already.", not "Will break your program and make you waste uncounted hours debugging if receiver has already started." Or how about preventing this in the code? Is there some scenario where you'd want to call start after the object has already started?

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Various Python related things

  • Python Magazine published my article "Using Dependency Injection in Python" in their August issue. Doug Hellman saw my blog entry about DI when I was switching web hosting and managed to repost old stuff to Planet Python, contacted me to ask if I wanted to expand on it a bit, I said yes, and now I've been published. Which is nice. I basically argue in the article that dependency injection is a good idea and you don't need to buy into a framework to get many of the benefits and provide some examples on how to do it. Which seems kind of apropos, seeing as there's yet another new contestant in that area.
  • I was hacking on something I wrote in Python recently and was doing it in a pretty heavily dependency injected manner, writing tests as I was going along. It came to me that one really basic, really nice thing about Python that isn't discussed all that much is that callables are duck typed and there are multiple choices on how to implement them. When you write a function that takes as a parameter something it calls to acquire values it doesn't have to care what the thing it's been given actually is. It can be a function, a callable, a bound method, a constructor, a lambda expression or even a generator. The caller doesn't have to care. It's not a language feature that's easy to fit in a bullet point or to appreciate without using it, but it is useful.
  • I was excited to see class decorators are coming in Python 2.6. Then I realized I can't remember what I wanted to use them for when I was really frustrated by their absence, but still, it's good. I always found their absence rather puzzling.
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Flow 08: Saturday and Sunday

On Saturday, it was raining cats and dogs. We were appropriately equipped and sniggered at the people in trainers etc trying to dodge the puddles. However, didn't see too many acts — saw a bit of Sébastien Tellier, but decided the crowds were too much and went to find some food (which was excellent and at 25 € for a three course vegetarian menu pretty good value.)

Next up on our schedule was CSS, which was pretty good. For some reason, it has never quite clicked for me, but still, they were busy as hell and obviously having fun.

And finally, The Roots. What a great show. No bling, no diva manners, just excellent hip hop with a surprising amount of jazz thrown in, just like on their early albums. And an incredibly diverse band, with Captain Kirk shredding his guitar and Tuba Gooding Jr on sousaphone.

Saturday was the only day it really felt like there were too many people stuffed into too small a space. Maybe it was the rain, maybe it was the fact that it was sold out, even though I don't think the other two days were that far behind.

On Sunday we were definitely starting to feel old and tired. It's surprising how tiring three days of festival gets, even without excessive drinking. Maybe I'm just too old. While eating on Saturday, I had the idea that they really should offer a show and dinner version of the festival; they already have an excellent restaurant on board, now just stretch out the dinner experience a bit and place the restaurant in a suitable location, and hey, the middle aged among us could be nice and comfy while checking out the gigs. And I really think they should have put the restaurant on the roof of the newer (if it is newer, the black one) gasometer.

We caught a glimpse of Astro Can Caravan, who had the weirdo jazz thing pretty well covered. Next up was The Five Corners Quintet, whose retro jazz was excellent as always. After that, we first checked out Plutonium 74, and had enough after one and a half songs. We listened to the first two or three songs from Señor Coconut and while their version of Daft Punk's Around the World wasn't horrible it wasn't nowhere near as good as Christian Prommer's on Friday, and by the time they hit Eurythmics' Sweet Dreams, we decided we had had enough of that too.

The next act we saw was José James who was one of the high points of the festival. He did a surprisingly jazzy gig and the crowd appreciated. After his gig, we listened for a couple of songs by Cut Copy, who really revealed themselves to be very summery party pop. Loud summery party pop. Their album In Ghost Colors was decent but I didn't get into it all that much, but they were better live. However, we were just too tired at that point and after a while headed home.

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Flow08, Day 1

Flow08 started off a whole lot better than last year. Everything worked smoothly despite the fact that there were twice as many people and twice as large an area as last year. In fact, the enlarged space felt better than the more constrained area of last year, maybe because we got to see more of the Suvilahti grounds.

Jamie Lidell

Artists we saw:

  • Jamie Lidell was a positive surprise. I found a video I saw earlier a bit meh, but his show was energetic and fun, moving from style to style effortlessly.
  • Kings of Convenience and Múm were both nice enough and lots of people seemed to enjoy them a lot, but... eh, not really Friday night music? Múm did occasionally manage to get a bit of a rhythm going, but they were more in the artsy fartsy moody camp I'd rather listen on my headphones. Both would have been better on Saturday or Sunday afternoon.
  • 22-Pistepirkko was excellent. It's not like they are a new band, but it was the first time I saw them live. They were loud, some of the songs got completely different treatments than on their albums, and the feeling was great.
  • Christian Prommer's Drumlesson was fabulous. The guys got an incredible groove going from the start, jazzing straight into the hedonistic heart of dance music.

Some mostly lousy pics on Flickr. Maybe Marko will post some better ones.

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