(Django Positions needs a new maintainer) A Django field for custom model ordering
This module provides PositionField, a model field for Django that allows instances of a model to be sorted by a user-specified position. Conceptually, the field works like a list index: when the position of one item is changed, the positions of other items in the collection are updated in response.
Add a PositionField to your model; that’s just about it.
If you want to work with all instances of the model as a single collection, there’s nothing else required. To create collections based on one or more fields on the model, specify the field names using the collection argument.
The apps in positions.examples demonstrate the PositionField API.
In general, the value assigned to a PositionField will be handled like a list index, to include negative values. Setting the position to -2 will cause the item to be moved to the second position from the end of collection – unless, of course, the collection has fewer than two elements.
Behavior varies from standard list indices when values greater than or less than the maximum or minimum positions are used. In those cases, the value is handled as being the same as the maximum or minimum position, respectively. None is also a special case that will cause an item to be moved to the last position in its collection.
The PositionManager custom manager uses PositionQuerySet to provide a reposition method that will update the position of all objects in the queryset to match the current ordering. If reposition is called on the manager itself, all objects will be repositioned according to the default model ordering.
Be aware that, unlike repositioning objects one at a time using list indices, the reposition method will call the save method of every model instance in the queryset.
Specifying a ManyToManyField as a collection won’t work; use an intermediate model with a PositionField instead:
class Product(models.Model): name = models.CharField(max_length=50) class Category(models.Model): name = models.CharField(max_length=50) products = models.ManyToManyField(Product, through='ProductCategory', related_name='categories') class ProductCategory(models.Model): product = models.ForeignKey(Product) category = models.ForeignKey(Category) position = PositionField(collection='category') class Meta(object): unique_together = ('product', 'category')
By default, if a parent model has a position field that declares a collection, child model instances are ordered independently. This behavior can be changed by specifying a parent_link argument identifying the name of the one-to-one field linking the child model to the parent. If parent_link is set, all subclass instances will be part of a single sequence in each collection.