Generic drag-and-drop ordering for objects in the Django admin interface
Another generic drag-and-drop ordering for sorting objects in the list view of the Django admin interface. It is a rewrite of https://github.com/iambrandontaylor/django-admin-sortable using another approach.
This plugin offers a simple mixin class which augments the functionality of an existing admin interface. It thus makes it very easy to integrate with existing models and their model admin interfaces.
The admin interface slightly modifies the list view of a sortable model. Next to the action checkbox, a draggable area is added to each entry line. The user than may click on any item and vertically drag that item to a new position.
If one or more items shall be moved to another page, this can easily been done by selecting them though the action checkbox, followed by using a predefined action from the pull down menu on the top of the list view.
pip install django-admin-sortable2
pip install -e git+https://github.com/jrief/django-admin-sortable2#egg=django_admin_sortable2
Add adminsortable to your INSTALLED_APPS.
Integrate your models
Each database model you want to sort, requires a position value in its model description. Rather than defining a base class, which contains such a positional value in a hard coded field, this plugin lets reuse existing fields or attempts to delegate this responsibility to the programmer. Therefore this plugin can be applied in situations, where your model is derived from an existing abstract model, which already contains any kind of position value. The only requirement for this plugin is, that this position value is specified as the default ordering.
If you specify a database model, make sure it contains an integer field to store the position value. This field must be set as the default ordering. Any existing model can be turned into a sortable model by adding two lines of code to the file models.py:
from django.db import models class MyModel(models.Model): ... other fields ... position = models.PositiveIntegerField(db_index=True, blank=False, null=False) class Meta(object): ordering = ['position']
You are free to use any name for the field named position here. Just make sure, that it is the first one in the list ordering in the class Meta.
In admin.py, add a mixin class to augment the functionality for sorting:
from django.contrib import admin from adminsortable.admin import SortableAdminMixin from myapp.models import MyModel class MyModelAdmin(SortableAdminMixin, admin.ModelAdmin): pass admin.site.register(MyModel, MyModelAdmin)
that’s it! The list view of the model admin interface now adds a column with a sensitive area. By clicking on that area, the user can move that row up or down. If he wants to move it to another page, he can do that as a bulk operation, using the admin actions.
In case you just changed your model to contain an additional field named, say order, which does not yet contain any values, then you may set initial ordering values by typing this code snipped into your Django shell:
shell> ./manage.py shell Python 2.7.3 (default, Jul 24 2012, 10:05:38) >>> from synthesa.models import * order = 0 for obj in MySortableModel.objects.all(): order += 1 obj.position = order obj.save()
or by using South migrations:
shell> ./manage.py datamigration myapp set_order
this creates an empty migration named something like myapp/migrations/0123_set_order.py. Edit this file and create a data migration:
class Migration(DataMigration): def forwards(self, orm): order = 0 for obj in orm.MyModel.objects.all(): order += 1 obj.position = order obj.save()
Should I add a unique index to the position field?
MySQL has a feature (or bug?) which requires to use the ORDER BY clause in bulk updates on unique fields.
SQLite has the same feature (or bug?) which is even worse, because it does not allow you to use the ORDER BY clause in bulk updates.
Only Postgres does it “right” in the sense, that it updates all fields in one transaction and afterwards rebuilds the unique index. Here one can not use the ORDER BY clause in bulk updates, which is senseless anyway.
See https://code.djangoproject.com/ticket/20708 for details.
Therefore I strongly advise against setting unique=True on the position field, unless you want unportable code, which only works with Postgres databases.
- Tabular and stacked inlines.
Why another plugin?
All available plugins which add functionality to make list views for the Django admin interface sortable, offer a base class to be used instead of models.Model. This abstract base class then contains a hard coded position field, additional methods and meta directives. The problem with this approach is twofold. First, an IS-A relationship is abused to augment the functionality of a class. This is bad OOP practice. A base class shall only be used to reflect a real IS-A relation which specializes this base class. For instance: A mammal is an animal, a primate is a mammal, homo sapiens is a primate, etc. Here the inheritance model is appropriate, but it would be wrong to derive from homo sapiens to reflect a human which is able to hunt using bows and arrows.
So, a sortable model is not an unsortable model. Making a model sortable, means to augment its functionality. This in OOP design does not qualify for an IS-A relationship.
Fortunately, Python makes it very easy, to distinguish between IS-A relationships and augmenting functionality. The latter cases are handled by mixin classes. They offer additional functionality for a class, without deriving from the base class.
Also consider the case, when someone wants to augment some other functionality of a model class. If he also derives from models.Model, he would create another abstract intermediate class. Someone who wants to use both functional augmentations, now is in trouble. Or he has to choose between one of the two, or if he derives from both, his model class inherits the base class models.Model twice.
By using a mixin class rather than deriving from a special abstract base class, these problems can be avoided!
- 0.0.1 first working release.
- 0.1.0 first version published on PyPI.
- 0.1.1 Fixed compatibility issue when used together with django-cms.
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