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/

Requires:

• Django >=1.8
• Python 2.7 or >=3.3

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 neighouring 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()}

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 seperate 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')

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)

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 the following in the admin.py file:

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

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

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

    def get_urls(self):
        urls = super(PizzaAdmin, self).get_urls()
        for inline in self.inlines:
            if hasattr(inline, 'get_urls'):
                urls = inline.get_urls(self) + urls
        return urls

admin.site.register(Pizza, PizzaAdmin)

Test suite

Requires Docker.

$ script/test