django-admin-sortable2 0.2.1

Generic drag-and-drop ordering for objects in the Django admin interface

django-admin-sortable2
======================

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 simple mixin classes which augment the functionality of *any* existing class
derived from ``admin.ModelAdmin``, ``admin.StackedInline`` or ``admin.TabluarInline``. It thus
makes it very easy to integrate with existing models and their model admin interfaces.

These admin mixin classes slightly modify the admin views of a sortable model. There is no need
to derive your model class from a special base model class, nor you have to add a hard coded
ordering field to your model. Use your existing ordered models, just as you always did.

Build status
------------
[](https://travis-ci.org/jrief/django-admin-sortable2)

Installation
------------
From PyPI:

pip install django-admin-sortable2

From github:

pip install -e git+https://github.com/jrief/django-admin-sortable2#egg=django_admin_sortable2

In ``settings.py`` add:

INSTALLED_APPS = (
...
'adminsortable',
...
)

Integrate your models
---------------------
Each database model which shall be sortable, 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 primary field used for sorting. This in
Django is declared through the model Meta class. Example ``models.py``:

class SortableBook(models.Model):
title = models.CharField('Title', null=True, blank=True, max_length=255)
my_order = models.PositiveIntegerField(blank=False, null=False)

class Meta(object):
ordering = ('my_order',)

Here the ordering field is named ``my_order``, but any other name is valid as well. The only
requirement is, that ``my_order`` is the first field in ``ordering`` in the model's Meta class.

The field used to store the ordering position may be any kind of numeric model field offered by
Django. Use one of these models fields:
* ``models.BigIntegerField``
* ``models.IntegerField``
* ``models.PositiveIntegerField`` (recommended)
* ``models.PositiveSmallIntegerField`` (recommended for small sets)
* ``models.SmallIntegerField``

These model fields also work, but are not recommended:
* ``models.DecimalField``
* ``models.FloatField``

Do not make this field unique!

Make a list view sortable
-------------------------
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. Then the user shall click on a predefined action from the pull down
menu on the top of the list view.

##### Integrate into a list view
In ``admin.py``, add a mixin class to augment the functionality for sorting:

from django.contrib import admin
from adminsortable.admin import SortableAdminMixin
from 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.

Make a stacked or tabular inline view sortable
----------------------------------------------
The interface for a sortable stacked inline view looks exactly the same. If you click on an
stacked inline's field title, this whole inline form can be moved up and down.

The interface for a sortable tabular inline view adds a sensitive area to each draggable row. These
rows then can be moved up and down.


After moving a tabular or stacked inline, save the model form to persist its sorting order.

##### Integrate into a detail view:

from django.contrib import admin
from adminsortable.admin import SortableInlineAdminMixin
from models import MySubModel, MyModel

class MySubModelInline(SortableInlineAdminMixin, admin.TabularInline): # or admin.StackedInline
model = MySubModel

class MyModelAdmin(admin.ModelAdmin):
inlines = (MySubModelInline,)
admin.site.register(MyModel, MyModelAdmin)

Initial data
------------
In case you just changed your model to contain an additional field named, say ``my_order``, which
does not yet contain any values, then you may set initial ordering values by pasting this code
snipped into the Django shell:

shell> ./manage.py shell
Python ...
>>>
from myapp.models import *
order = 0
for obj in MySortableModel.objects.all():
order += 1
obj.my_order = order
obj.save()

or using South migrations:

shell> ./manage.py datamigration myapp set_order

this creates an empty migration named something like ``migrations/0123_set_order.py``. Edit
the file and change it into a data migration:

class Migration(DataMigration):
def forwards(self, orm):
order = 0
for obj in orm.MyModel.objects.all():
order += 1
obj.my_order = order
obj.save()

then apply the changes to the database using:

shell> ./manage.py migrate myapp

Note on unique indices on the position field
--------------------------------------------
From a design consideration, one might be tempted to add a unique index on the ordering field. But
in practice this has serious drawbacks:

MySQL has a feature (or bug?) which requires to use the ``ORDER BY`` clause in bulk updates on
unique fields.

SQLite has the same bug which is even worse, because it does neither update all the fields in one
transaction, nor does it allow to use the ``ORDER BY`` clause in bulk updates.

Only PostgreSQL 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 during 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.

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 such
an 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 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 real IS-A relationships and augmenting
functionalities. 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. In the latter case, his model class inherits
the base class ``models.Model`` twice. This results in a diamond shape inheritance, which shall
be avoided under all circumstances.

By using a mixin class rather than deriving from a special abstract base class, these problems
can be avoided!

Related projects
================
* https://github.com/iambrandontaylor/django-admin-sortable
* https://github.com/mtigas/django-orderable
* http://djangosnippets.org/snippets/2057/
* http://djangosnippets.org/snippets/2306/
* http://catherinetenajeros.blogspot.co.at/2013/03/sort-using-drag-and-drop.html

Release history
===============
* 0.2.0 Added sortable stacked and tabular inlines.
* 0.1.2 Fixed: All field names other than "order" are now allowed.
* 0.1.1 Fixed compatibility issue when used together with django-cms.
* 0.1.0 first version published on PyPI.
* 0.0.1 first working release.