Django snippets

# -------- the usage (the good stuff first)

# models.py

class Category(OrderedModel):
    name = models.CharField(max_length=50)

    def __unicode__(self):
        return self.name

# admin.py
class CategoryAdmin(admin.ModelAdmin):
    list_display = ('name', 'order', 'order_link') # notice the order_link !!
admin.site.register(Category, CategoryAdmin)




# -------- the metaclass

from django.contrib.contenttypes.models import ContentType
from django.core.urlresolvers import reverse
from django.db import models

class OrderedModel(models.Model):
    order = models.PositiveIntegerField(editable=False)

    def save(self):
        if not self.id:
            try:
                self.order = self.__class__.objects.all().order_by("-order")[0].order + 1
            except IndexError:
                self.order = 0
        super(OrderedModel, self).save()
        

    def order_link(self):
        model_type_id = ContentType.objects.get_for_model(self.__class__).id
        model_id = self.id
        kwargs = {"direction": "up", "model_type_id": model_type_id, "model_id": model_id}
        url_up = reverse("admin-move", kwargs=kwargs)
        kwargs["direction"] = "down"
        url_down = reverse("admin-move", kwargs=kwargs)
        return '<a href="%s">up</a> | <a href="%s">down</a>' % (url_up, url_down)
    order_link.allow_tags = True
    order_link.short_description = 'Move'
    order_link.admin_order_field = 'order'


    @staticmethod
    def move_down(model_type_id, model_id):
        try:
            ModelClass = ContentType.objects.get(id=model_type_id).model_class()

            lower_model = ModelClass.objects.get(id=model_id)
            higher_model = ModelClass.objects.filter(order__gt=lower_model.order)[0]
            
            lower_model.order, higher_model.order = higher_model.order, lower_model.order

            higher_model.save()
            lower_model.save()
        except IndexError:
            pass
        except ModelClass.DoesNotExist:
            pass
                
    @staticmethod
    def move_up(model_type_id, model_id):
        try:
            ModelClass = ContentType.objects.get(id=model_type_id).model_class()

            higher_model = ModelClass.objects.get(id=model_id)
            lower_model = ModelClass.objects.filter(order__lt=higher_model.order)[0]

            lower_model.order, higher_model.order = higher_model.order, lower_model.order

            higher_model.save()
            lower_model.save()
        except IndexError:
            pass
        except ModelClass.DoesNotExist:
            pass

    class Meta:
        ordering = ["order"]
        abstract = True


# -------- the view

from django.contrib.admin.views.decorators import staff_member_required
from django.contrib.contenttypes.models import ContentType
from django.http import HttpResponseRedirect
from models import OrderedModel
from django.db import transaction

@staff_member_required
@transaction.commit_on_success
def admin_move_ordered_model(request, direction, model_type_id, model_id):
    if direction == "up":
        OrderedModel.move_up(model_type_id, model_id)
    else:
        OrderedModel.move_down(model_type_id, model_id)
    
    ModelClass = ContentType.objects.get(id=model_type_id).model_class()
    
    app_label = ModelClass._meta.app_label
    model_name = ModelClass.__name__.lower()

    url = "/admin/%s/%s/" % (app_label, model_name)
    
    return HttpResponseRedirect(url)


# -------- the url config

urlpatterns = patterns('',
    # ...
    url(r'^admin/orderedmove/(?P<direction>up|down)/(?P<model_type_id>\d+)/(?P<model_id>\d+)/$', 'your.views.admin_move_ordered_model', name="admin-move"),
    # ...
)