django-ltree

A Django implementation for PostgreSQL's ltree extension, providing efficient storage and querying of hierarchical tree-like data.

See PostgreSQL's ltree documentation to learn more about it.

The main benefits of ltree:

• Efficient path queries (ancestors, descendants, pattern matching)
• Index-friendly hierarchical storage
• Powerful label path searching
• Native PostgreSQL performance for tree operations

Features

• Django model fields for ltree data types
• Query utilities for common tree operations
• Migration support for ltree extension installation
• Compatibility with Django's ORM and query syntax

Requirements

• Django 5.2+
• Python 3.11+
• PostgreSQL 16+ (with ltree extension enabled)

Installation

1. Install the package:

   pip install django-ltree
   

2. Add to your INSTALLED_APPS:

   INSTALLED_APPS = [
       ...
       "django_ltree",
       ...
   ]
   

3. Run migrations to install the ltree extension:

   python manage.py migrate django_ltree
   

Usage

django-ltree provides a base model class called TreeModel.

TreeModel does these things out of the box:

• adds a field called path to your model (by default, path is created by items Id plus parent's path)
• adds t_objects which is the TreeManager you can use to work with tree data
• adds two indexes for path (one BTreeIndex, one GistIndex)
• orders items base on path

if you are overriding the Meta class of your model, you may want to inherit from TreeModel.Meta.

  class Meta(TreeModel.Meta):

to keep the indexes and ordering.

Quick Start

1. inherit from TreeModel:

   from django_ltree.models import TreeModel
   
   class Category(TreeModel):
       name = models.CharField(max_length=50)
   

2. Create tree nodes:

   # make an item without a parent (root)
   root = Category.t_objects.create(name="Root")
   # make a child item
   child = Category.t_objects.create_child(name="Child", parent=root)
   # you can also use `add_child` directly on root
   child2 = root.add_child(name="another child")
   

note that path is handled by django-ltree, you don't need to pass any value for it

3. Query ancestors and descendants:

   # Get all ancestors
   child.ancestors()
   
   # Get all descendants
   child.descendants()
   

Alternate paths

paths are made using the objects id and (if exists) it's parent's path.

if you need to use a different field for path generation, configure it like this:

  class Role(TreeModel):
      name = CharField()

      t_objects = TreeManager(path_field="name")

now paths are created using the name field

  su = Role.t_objects.create(name="SuperUser")
  print(su.path)  # SuperUser
  admin = su.add_child(name="Admin")
  print(admin.path)  # SuperUser.Admin

when using an alternative field for path generation, it is recommended to use a field that ensures uniqueness to avoid confilicts.

if you are using a field that is not auto-generated (like name in the example above), it is recommended to overwrite TreeManager.create and TreeManager.create_child like this:

class MyTreeManager(TreeManager):
    def create(self, **kwargs):
        """create an item with no parents (root)"""
        kwargs["path"] = PathValue([kwargs[self.path_field]])
        obj = self._create(**kwargs)

        return obj

    def create_child(self, parent: "TreeModel | PathValue | None" = None, **kwargs):
        if not parent:
            return self.create(**kwargs)

        prefix = parent.path if isinstance(parent, models.Model) else parent
        kwargs["path"] = PathValue([*prefix, kwargs[self.path_field]])

        obj = self._create(**kwargs)
        return obj

for slightly better performance and less overhead.

this does not work for auto-generated fields like id.

TreeModel methods

TreeModel has the following methods:

1. label(self): returns the last part of path

2. ancestors(self): return all the ancestors of the current item, including the item itself (use t_objects.ancestors_of(item) if you don't want the item included)

3. descendants(self): return all the descendants of the current item, including the item itself (use t_objects.descendants_of(item) if you don't want the item included)

4. parent(self): return the immediate parent of the current item, or None if the item is a root

5. get_root(self): return the root parent of this item

6. children(self): return all the immediate children of the current item

7. siblings(self): return all the siblings of the current item (items that share the same parent with this item), not including the item itself

8. add_child(self, **kwargs): create a child for this item kwargs are the arguments used to make the child (the model fields)

9. get_ancestors_paths(self): return the paths of all the ancestors of the current item (not including the item's own path) as a list of PathValue

10. change_parent(self, new_parent): change the parent of the current item (this moves the item and all it's descendants to be under another item) new_parent is either a object of the same model, or the path value of an object returns the number of rows updated

11. make_root(self): move the current item to be a root item (moves the item and all it's descendants) returns the number of rows updated

12. delete(self, cascade=False, **kwargs): deletes the current item if cascade is True, all the descendants are also deleted, otherwise the children will move under the deleted item's parent (or become root items if the deleted item was a root)

13. delete_cascade(self, **kwargs): delete the current item and all it's descendants

TreeManager methods

TreeManager has the following methods

1. create_child(self, parent=None, **kwargs): creates an item if parent is provided, it will become the parent item of the created item, otherwise creation will happen as root parent can be a model instance or a PathValue kwargs are the model fields used to create the item (any path passed in is ignored, it is always generated)

2. create(self, **kwargs): create a root item kwargs are the model fields used to create the item (any path passed in is ignored, it is always generated)

3. roots(self): return all the root items from database

4. children(self, node): return all the immediate children of node node can be a model instance, a PathValue, a string like "1.2.3", or a list of labels

5. descendants_of(self, node, include_self=False, max_depth=None): return the descendants of node by default the node itself is not included, pass include_self=True to include it max_depth limits how many levels below the node to include this compiles to a single indexed lquery match, e.g. path ~ '1.2.*{1,3}'

6. ancestors_of(self, node, include_self=False): return the ancestors of node by default the node itself is not included, pass include_self=True to include it

# the whole subtree under a category, excluding the category itself
Category.t_objects.descendants_of(category)

# only two levels deep, e.g. for building a menu
Category.t_objects.descendants_of(category, max_depth=2)

# breadcrumbs: all ancestors from the root down, including the item
Category.t_objects.ancestors_of(category, include_self=True)

roots, children, descendants_of, and ancestors_of are also available on querysets, so they can be chained with regular filters:

Category.t_objects.filter(is_active=True).descendants_of(category, max_depth=2)

lookups and functions

for a list of all available operations and functions for ltree check https://www.postgresql.org/docs/current/ltree.html#LTREE-OPS-FUNCS

provided lookups

1. exact (same as = in postgresql) TreeModel.t_objects.filter(path__exact=path)

2. ancestors (same as @> in postgresql) TreeModel.t_objects.filter(path__ancestors=path)

3. descendants (same as <@ in postgresql) TreeModel.t_objects.filter(path__descendants=path)

4. match (same as ~ in postgresql) TreeModel.t_objects.filter(path__match=f"{self.path}.*{{1}}")

5. contains (same as ? in postgresql) takes a list (or tuple) of lquery patterns and matches items whose path matches any of them; passing a single string raises a TypeError TreeModel.t_objects.filter(path__contains=["1.*", "2.*"])

6. depth (calls NLEVEL function from postgresql) TreeModel.t_objects.filter(path__depth=len(path) + 1) it is a transform, so it can be combined with other lookups, e.g. path__depth__lt=3

provided functions

1. django_ltree.functions.NLevel same as NLEVEL function from postgresql

2. django_ltree.functions.Subpath same as SUBPATH functions from postgresql

for concatenation (||) you can use django.db.models.functions.Concat

Documentation

For complete documentation, see [TODO: Add Documentation Link].

Links

• Source Code: https://github.com/mariocesar/django-ltree
• Bug Reports: https://github.com/mariocesar/django-ltree/issues
• PyPI Package: https://pypi.org/project/django-ltree/
• PostgreSQL ltree Docs: https://www.postgresql.org/docs/current/ltree.html

Contributing

Contributions are welcome! Please see CONTRIBUTING.md for guidelines.

License

MIT License