Every now and then you need to have items in your database which have a specific order. As SQL does not save rows in any order, you need to take care about this for yourself. No - actually, you don't need to anymore. You can just use this file - it is designed as kind-of plug-in for the Django ORM.
Usage is (due to use of meta-classes) quite simple. It is recommended to save this snippet into a separate file called `positional.py`. To use it, you only have to import `PositionalSortMixIn` from the `positional` module and inherit from it in your own, custom model (but *before* you inherit from `models.Model`, the order counts).
Usage example: Add this to your `models.py`
from positional import PositionalSortMixIn
class MyModel(PositionalSortMixIn, models.Model):
name = models.CharField(maxlength=200, unique=True)
Now you need to create the database tables: `PositionalSortMixIn` will automatically add a `postition` field to your model. In your views you can use it simply with `MyModel.objects.all().order_by('position')` and you get the objects sorted by their position. Of course you can move the objects down and up, by using `move_up()`, `move_down()` etc.
In case you feel you have seen this code somewhere - right, this snippet is a modified version of [snippet #245](/snippets/245/) which I made earlier. It is basically the same code but uses another approach to display the data in an ordered way. Instead of overriding the `Manager` it adds the `position` field to `Meta.ordering`. Of course, all of this is done automatically, you only need to use `YourItem.objects.all()` to get the items in an ordered way.
Update: Now you can call your custom managers `object` as long as the default manager (the one that is defined first) still returns all objects. This Mix-in absolutely needs to be able to access all elements saved.
In case you find any errors just write a comment, updated versions are published here from time to time as new bugs are found and fixed.
- db
- orm
- database
- plugin
- mixin
If you have a model that has an "ordering" column, and you want to be able to re-position records (eg, order items by priority), this base class should make it fairly easy. To use it, you extend your model using this abstract class, then hook up the pre_save event to the pre_save event of the base class, and you're good to go. Whenever you save an item, it ensures that it has a valid "order" number. The meat of this class is the "move()" method. Just call instance.move(number) where instance is your model instance, and this class will do all the logic necessary to shift around the order numbers for you.
- sort
- order
- sortable
- orderable
- sorted
- ordered