django-admin-sortable2 0.2.3

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

Project home: https://github.com/jrief/django-admin-sortable2

Ask questions and report bugs on:
https://github.com/jrief/django-admin-sortable2/issues

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

This is another generic drag-and-drop ordering module 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 an
unintrusive 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
------------

|Build Status|

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.

.. figure:: docs/list-view.png
:alt: Sortable List View

Sortable List View
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.

.. figure:: docs/tabular-inline.png
:alt: Sortable Tabular Inlines

Sortable Tabular Inlines
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!

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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
===============

- 0.2.2 Distinction between different versions of jQuery in case
django-cms is installed side by side.
- 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.

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