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from django.core.exceptions import ValidationError
from django.db import models
from django.db.models import Max
from django.utils.translation import gettext_lazy as _
from tree_queries.fields import TreeNodeForeignKey
from tree_queries.query import TreeQuerySet
class TreeNode(models.Model):
parent = TreeNodeForeignKey(
"self",
blank=True,
null=True,
on_delete=models.CASCADE,
verbose_name=_("parent"),
related_name="children",
)
objects = TreeQuerySet.as_manager()
class Meta:
abstract = True
def ancestors(self, **kwargs):
"""
Returns all ancestors of the current node
See ``TreeQuerySet.ancestors`` for details and optional arguments.
"""
return self.__class__._default_manager.ancestors(self, **kwargs)
def descendants(self, **kwargs):
"""
Returns all descendants of the current node
See ``TreeQuerySet.descendants`` for details and optional arguments.
"""
return self.__class__._default_manager.descendants(self, **kwargs)
def clean(self):
"""
Raises a validation error if saving this instance would result in loops
in the tree structure
"""
super().clean()
if (
self.parent_id
and self.pk
and (
self.__class__._default_manager.ancestors(
self.parent_id, include_self=True
)
.filter(pk=self.pk)
.exists()
)
):
raise ValidationError(_("A node cannot be made a descendant of itself."))
class OrderableTreeNode(TreeNode):
"""
A TreeNode with automatic position management for consistent sibling ordering.
This mixin provides automatic position value assignment when creating new nodes,
ensuring siblings are properly ordered. When a node is saved without an explicit
position value, it automatically receives a position 10 units higher than the
maximum position among its siblings.
Usage:
class Category(OrderableTreeNode):
name = models.CharField(max_length=100)
# position field and ordering are provided by OrderableTreeNode
The position field increments by 10 (rather than 1) to make it explicit that
the position values themselves have no inherent meaning - they are purely for
relative ordering, not a sibling counter or index. This approach is identical
to the one used in feincms3's AbstractPage.
"""
position = models.PositiveIntegerField(default=0, db_index=True)
class Meta:
abstract = True
ordering = ["position"]
def save(self, *args, **kwargs):
"""
Automatically assigns a position value if not set.
If the position is 0 (the default), calculates a new position by finding
the maximum position among siblings and adding 10.
"""
if not self.position:
self.position = 10 + (
self.__class__._default_manager.filter(parent_id=self.parent_id)
.order_by()
.aggregate(p=Max("position"))["p"]
or 0
)
super().save(*args, **kwargs)
save.alters_data = True
|
