django-ordered-model

by bfirsh

Get your Django models in order

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django-ordered-model

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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

$ python setup.py install

You can use Pip:

$ pip install django-ordered-model

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)

class Meta(OrderedModel.Meta):
    pass

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()

previous() and next() get the neighbouring objects directly above of below within the ordered stack depending on the direction.

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,
OrderedModelManager
, which provides additional operations on the resulting
QuerySet
. For example an
OrderedModel
subclass called
Item
that returns a queryset from
Item.objects.all()
supports the following functions:
  • above_instance(object)
    ,
  • below_instance(object)
    ,
  • get_min_order()
    ,
  • get_max_order()
    ,
  • above(index)
    ,
  • below(index)

If your model defines a custom

ModelManager
such as
ItemManager
below, you may wish to extend
OrderedModelManager
to retain those functions, as follows:
from ordered_model.models import OrderedModelManager, OrderedModel

class ItemManager(OrderedModelManager): pass

class Item(OrderedModel): objects = ItemManager()

Custom ordering field

Extending

OrderedModel
creates a
models.PositiveIntegerField
field called
order
and the appropriate migrations. If you wish to use an existing model field to store the ordering, you can set the attribute
order_field_name
to match your field name:
class MyModel(OrderedModelBase):
    ...
    sort_order = models.PositiveIntegerField(editable=False, db_index=True)
    order_field_name = "sort_order"

class Meta:
    ordering = ("sort_order",)

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

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

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

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

admin.site.register(Pizza, PizzaAdmin)

Test suite

Requires Docker.

$ script/test

Compatibility with Django and Python

|django-ordered-model version | Django version | Python version |-----------------------------|---------------------|-------------------- | 3.4.x | 2.x | 3.5 and above | 3.3.x | 2.x | 3.4 and above | 3.2.x | 2.x | 3.4 and above | 3.1.x | 2.x | 3.4 and above | 3.0.x | 2.x | 3.4 and above | 2.1.x | 1.x | 2.7 to 3.6 | 2.0.x | 1.x | 2.7 to 3.6

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