django-ordered-model

django-ordered-model allows models to be ordered and provides a simple admin interface for reordering them.

Based on https://djangosnippets.org/snippets/998/ and https://djangosnippets.org/snippets/259/

See our compatability notes for the appropriate version to use with older Django and Python releases.

Installation

Please install using Pip:

$ pip install django-ordered-model

Or if you have checked out the repository:

$ python setup.py install

Or to use the latest development code from our master branch:

$ pip uninstall django-ordered-model
$ pip install git+git://github.com/django-ordered-model/django-ordered-model.git

Usage

Add ordered_model to your SETTINGS.INSTALLED_APPS.

Inherit your model from OrderedModel to make it ordered:

from django.db import models
from ordered_model.models import OrderedModel


class Item(OrderedModel):
    name = models.CharField(max_length=100)

Then run the usual $ ./manage.py makemigrations and $ ./manage.py migrate to update your database schema.

Model instances now have a set of methods to move them relative to each other. To demonstrate those methods we create two instances of Item:

foo = Item.objects.create(name="Foo")
bar = Item.objects.create(name="Bar")

Swap positions

foo.swap(bar)

This swaps the position of two objects.

Move position up on position

foo.up()
foo.down()

Moving an object up or down just makes it swap its position with the neighbouring object directly above of below depending on the direction.

Move to arbitrary position

foo.to(12)
bar.to(13)

Move the object to an arbitrary position in the stack. This essentially sets the order value to the specified integer. Objects between the original and the new position get their order value increased or decreased according to the direction of the move.

Move object above or below reference

foo.above(bar)
foo.below(bar)

Move the object directly above or below the reference object, increasing or decreasing the order value for all objects between the two, depending on the direction of the move.

Move to top of stack

foo.top()

This sets the order value to the lowest value found in the stack and increases the order value of all objects that were above the moved object by one.

Move to bottom of stack

foo.bottom()

This sets the order value to the highest value found in the stack and decreases the order value of all objects that were below the moved object by one.

Updating fields that would be updated during save()

For performance reasons, the delete(), to(), below(), above(), top(), and bottom() methods use Django's update() method to change the order of other objects that are shifted as a result of one of these calls. If the model has fields that are typically updated in a customized save() method, or through other app level functionality such as DateTimeField(auto_now=True), you can add additional fields to be passed through to update(). This will only impact objects where their order is being shifted as a result of an operation on the target object, not the target object itself.

foo.to(12, extra_update={'modified': now()})

Get the previous or next objects

foo.previous()
foo.next()

The previous() and next() methods return the neighbouring objects directly above or below within the ordered stack.

Subset Ordering

In some cases, ordering objects is required only on a subset of objects. For example, an application that manages contact lists for users, in a many-to-one/many relationship, would like to allow each user to order their contacts regardless of how other users choose their order. This option is supported via the order_with_respect_to parameter.

A simple example might look like so:

class Contact(OrderedModel):
    user = models.ForeignKey(User, on_delete=models.CASCADE)
    phone = models.CharField()
    order_with_respect_to = 'user'

If objects are ordered with respect to more than one field, order_with_respect_to supports tuples to define multiple fields:

class Model(OrderedModel)
    # ...
    order_with_respect_to = ('field_a', 'field_b')

In a many-to-many relationship you need to use a separate through model which is derived from the OrderedModel. For example, an application which manages pizzas with toppings.

A simple example might look like so:

class Topping(models.Model):
    name = models.CharField(max_length=100)


class Pizza(models.Model):
    name = models.CharField(max_length=100)
    toppings = models.ManyToManyField(Topping, through='PizzaToppingsThroughModel')


class PizzaToppingsThroughModel(OrderedModel):
    pizza = models.ForeignKey(Pizza, on_delete=models.CASCADE)
    topping = models.ForeignKey(Topping, on_delete=models.CASCADE)
    order_with_respect_to = 'pizza'

    class Meta:
        ordering = ('pizza', 'order')

You can also specify order_with_respect_to to a field on a related model. An example use-case can be made with the following models:

class ItemGroup(models.Model):
    user = models.ForeignKey(User, on_delete=models.CASCADE)
    general_info = models.CharField(max_length=100)

class GroupedItem(OrderedModel):
    group = models.ForeignKey(ItemGroup, on_delete=models.CASCADE)
    specific_info = models.CharField(max_length=100)
    order_with_respect_to = 'group__user'

Here items are put into groups that have some general information used by its items, but the ordering of the items is independent of the group the item is in.

When you want ordering on the baseclass instead of subclasses in an ordered list of objects of various classes, specify the full module path of the base class:

class BaseQuestion(OrderedModel):
    order_class_path = __module__ + '.BaseQuestion'
    question = models.TextField(max_length=100)

    class Meta:
        ordering = ('order',)

class MultipleChoiceQuestion(BaseQuestion):
    good_answer = models.TextField(max_length=100)
    wrong_answer1 = models.TextField(max_length=100)
    wrong_answer2 = models.TextField(max_length=100)
    wrong_answer3 = models.TextField(max_length=100)

class OpenQuestion(BaseQuestion):
    answer = models.TextField(max_length=100)

Custom Manager and QuerySet

When your model your extends OrderedModel, it inherits a custom ModelManager instance which in turn provides additional operations on the resulting QuerySet. For example if Item is an OrderedModel subclass, the queryset Item.objects.all() has functions:

• above_instance(object),
• below_instance(object),
• get_min_order(),
• get_max_order(),
• above(index),
• below(index)

If your Model uses a custom ModelManager (such as ItemManager below) please have it extend OrderedModelManager.

If your ModelManager returns a custom QuerySet (such as ItemQuerySet below) please have it extend OrderedModelQuerySet.

from ordered_model.models import OrderedModel, OrderedModelManager, OrderedModelQuerySet

class ItemQuerySet(OrderedModelQuerySet):
    pass

class ItemManager(OrderedModelManager):
    def get_queryset(self):
        return ItemQuerySet(self.model, using=self._db)

class Item(OrderedModel):
    objects = ItemManager()

Custom ordering field

Extending OrderedModel creates a models.PositiveIntegerField field called order and the appropriate migrations. It customises the default class Meta to then order returned querysets by this field. If you wish to use an existing model field to store the ordering, subclass OrderedModelBase instead and set the attribute order_field_name to match your field name and the ordering attribute on Meta:

class MyModel(OrderedModelBase):
    ...
    sort_order = models.PositiveIntegerField(editable=False, db_index=True)
    order_field_name = "sort_order"

    class Meta:
        ordering = ("sort_order",)

Setting order_field_name is specific for this library to know which field to change when ordering actions are taken. The Meta ordering line is existing Django functionality to use a field for sorting. See tests/models.py object CustomOrderFieldModel for an example.

Admin integration

To add arrows in the admin change list page to do reordering, you can use the OrderedModelAdmin and the move_up_down_links field:

from django.contrib import admin
from ordered_model.admin import OrderedModelAdmin
from models import Item


class ItemAdmin(OrderedModelAdmin):
    list_display = ('name', 'move_up_down_links')

admin.site.register(Item, ItemAdmin)

For a many-to-many relationship you need one of the following inlines.

OrderedTabularInline or OrderedStackedInline just like the django admin.

For the OrderedTabularInline it will look like this:

from django.contrib import admin
from ordered_model.admin import OrderedTabularInline, OrderedInlineModelAdminMixin
from models import Pizza, PizzaToppingsThroughModel


class PizzaToppingsTabularInline(OrderedTabularInline):
    model = PizzaToppingsThroughModel
    fields = ('topping', 'order', 'move_up_down_links',)
    readonly_fields = ('order', 'move_up_down_links',)
    ordering = ('order',)
    extra = 1


class PizzaAdmin(OrderedInlineModelAdminMixin, admin.ModelAdmin):
    model = Pizza
    list_display = ('name', )
    inlines = (PizzaToppingsTabularInline, )


admin.site.register(Pizza, PizzaAdmin)

For the OrderedStackedInline it will look like this:

from django.contrib import admin
from ordered_model.admin import OrderedStackedInline, OrderedInlineModelAdminMixin
from models import Pizza, PizzaToppingsThroughModel


class PizzaToppingsStackedInline(OrderedStackedInline):
    model = PizzaToppingsThroughModel
    fields = ('topping', 'move_up_down_links',)
    readonly_fields = ('move_up_down_links',)
    ordering = ('order',)
    extra = 1


class PizzaAdmin(OrderedInlineModelAdminMixin, admin.ModelAdmin):
    list_display = ('name', )
    inlines = (PizzaToppingsStackedInline, )


admin.site.register(Pizza, PizzaAdmin)

Note: OrderedModelAdmin requires the inline subclasses of OrderedTabularInline and OrderedStackedInline to be listed on inlines so that we register appropriate URL routes. If you are using Django 3.0 feature get_inlines() or get_inline_instances() to return the list of inlines dynamically, consider it a filter and still add them to inlines or you might encounter a “No Reverse Match” error when accessing model change view.

Re-ordering models

In certain cases the models will end up in a not properly ordered state. This can be caused by bypassing the 'delete' / 'save' methods, or when a user changes a foreign key of a object which is part of the 'order_with_respect_to' fields. You can use the following command to re-order one or more models.

$ ./manage.py reorder_model <app_name>.<model_name> \
        [<app_name>.<model_name> ... ]

The arguments are as follows:
- `<app_name>`: Name of the application for the model.
- `<model_name>`: Name of the model that's an OrderedModel.

Django Rest Framework

To support updating ordering fields by Django Rest Framework, we include a serializer OrderedModelSerializer that intercepts writes to the ordering field, and calls OrderedModel.to() method to effect a re-ordering:

from rest_framework import routers, serializers, viewsets
from ordered_model.serializers import OrderedModelSerializer
from tests.models import CustomItem

class ItemSerializer(serializers.HyperlinkedModelSerializer, OrderedModelSerializer):
    class Meta:
        model = CustomItem
        fields = ['pkid', 'name', 'modified', 'order']

class ItemViewSet(viewsets.ModelViewSet):
    queryset = CustomItem.objects.all()
    serializer_class = ItemSerializer

router = routers.DefaultRouter()
router.register(r'items', ItemViewSet)

Note that you need to include the 'order' field (or your custom field name) in the Serializer's fields list, either explicitly or using __all__. See ordered_model/serializers.py for the implementation.

Test suite

To run the tests against your current environment, use:

$ django-admin test --pythonpath=. --settings=tests.settings

Otherwise please install tox and run the tests for a specific environment with -e or all environments:

$ tox -e py36-django30
$ tox

Compatibility with Django and Python

Maintainers

• Ben Firshman
• Chris Shucksmith
• Sardorbek Imomaliev