django-postgresql-dag 0.0.8

Directed Acyclic Graph implementation for Django & Postgresql

Django & Postgresql-based Directed Acyclic Graphs

The main distinguishing factor for this project is that it can retrieve entire sections of a graph in a single query. The trade off is portability: it uses Postgres Common Table Expressions (CTE) to achieve this and is therefore not compatible with other databases.

NOTE: Not all methods which would benefit from CTEs use them yet.

NOTE: This project is a work in progress. While functional, it is not optimized. Currently, it provides numerous methods for retrieving nodes, and a few for retrieving edges within the graph.

Most Simple Example:

models.py

from django.db import models
from django_postgresql_dag.models import node_factory, edge_factory

class NetworkEdge(edge_factory("NetworkNode", concrete=False)):
    name = models.CharField(max_length=100)

    def __str__(self):
        return self.name

    def save(self, *args, **kwargs):
        self.name = f"{self.parent.name} {self.child.name}"
        super().save(*args, **kwargs)


class NetworkNode(node_factory(NetworkEdge)):
    name = models.CharField(max_length=100)

    def __str__(self):
        return self.name

Add some Instances via the Shell (or in views, etc)

~/myapp$ python manage.py shell
>>> from myapp.models import NetworkNode, NetworkEdge

>>> root = NetworkNode.objects.create(name="root")

>>> a1 = NetworkNode.objects.create(name="a1")
>>> a2 = NetworkNode.objects.create(name="a2")
>>> a3 = NetworkNode.objects.create(name="a3")

>>> b1 = NetworkNode.objects.create(name="b1")
>>> b2 = NetworkNode.objects.create(name="b2")
>>> b3 = NetworkNode.objects.create(name="b3")
>>> b4 = NetworkNode.objects.create(name="b4")

>>> c1 = NetworkNode.objects.create(name="c1")
>>> c2 = NetworkNode.objects.create(name="c2")

>>> root.add_child(a1)
>>> root.add_child(a2)
>>> a3.add_parent(root)  # You can add from either side of the relationship

>>> b1.add_parent(a1)
>>> a1.add_child(b2)
>>> a2.add_child(b2)
>>> a3.add_child(b3)
>>> a3.add_child(b4)

>>> b3.add_child(c2)
>>> b3.add_child(c1)
>>> b4.add_child(c1)

Resulting Database Tables

myapp_networknode

 id | name
----+------
 1  | root
 2  | a1
 3  | a2
 4  | a3
 5  | b1
 6  | b2
 7  | b3
 8  | b4
 9  | c1
 10 | c2

myapp_networkedge

id  | child_id | parent_id | name
----+----------+-----------+---------
 1  |       2  |         1 | root a1
 2  |       3  |         1 | root a2
 3  |       4  |         1 | root a3
 4  |       5  |         2 | a1 b1
 5  |       6  |         2 | a1 b2
 6  |       6  |         3 | a2 b2
 7  |       7  |         4 | a3 b3
 8  |       8  |         4 | a3 b4
 9  |       10 |         7 | b3 c2
 10 |       9  |         7 | b3 c1
 11 |       9  |         8 | b4 c1

Diagramatic View

Work with the Graph in the Shell (or in views, etc)

~/myapp$ python manage.py shell
>>> from myapp.models import NetworkNode, NetworkEdge

# Descendant methods which return ids

>>> root.descendant_ids()
[2, 3, 4, 5, 6, 7, 8, 9, 10]
>>> root.self_and_descendant_ids()
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
>>> root.descendants_and_self_ids()
[10, 9, 8, 7, 6, 5, 4, 3, 2, 1]

# Descendant methods which return a queryset

>>> root.descendants()
<QuerySet [<NetworkNode: a1>, <NetworkNode: a2>, <NetworkNode: a3>, <NetworkNode: b1>, <NetworkNode: b2>, <NetworkNode: b3>, <NetworkNode: b4>, <NetworkNode: c1>, <NetworkNode: c2>]>
>>> root.self_and_descendants()
<QuerySet [<NetworkNode: root>, <NetworkNode: a1>, <NetworkNode: a2>, <NetworkNode: a3>, <NetworkNode: b1>, <NetworkNode: b2>, <NetworkNode: b3>, <NetworkNode: b4>, <NetworkNode: c1>, <NetworkNode: c2>]>
>>> root.descendants_and_self()
[<NetworkNode: c2>, <NetworkNode: c1>, <NetworkNode: b4>, <NetworkNode: b3>, <NetworkNode: b2>, <NetworkNode: b1>, <NetworkNode: a3>, <NetworkNode: a2>, <NetworkNode: a1>, <NetworkNode: root>]

# Ancestor methods which return ids

>>> c1.ancestor_ids()
[1, 4, 7, 8]
>>> c1.ancestor_and_self_ids()
[1, 4, 7, 8, 9]
>>> c1.self_and_ancestor_ids()
[9, 8, 7, 4, 1]

# Ancestor methods which return a queryset

>>> c1.ancestors()
<QuerySet [<NetworkNode: root>, <NetworkNode: a3>, <NetworkNode: b3>, <NetworkNode: b4>]>
>>> c1.ancestors_and_self()
<QuerySet [<NetworkNode: root>, <NetworkNode: a3>, <NetworkNode: b3>, <NetworkNode: b4>, <NetworkNode: c1>]>
>>> c1.self_and_ancestors()
[<NetworkNode: c1>, <NetworkNode: b4>, <NetworkNode: b3>, <NetworkNode: a3>, <NetworkNode: root>]

# Get the node's clan (all ancestors, self, and all descendants)

>>> b3.clan_ids()
[1, 4, 7, 9, 10]
>>> b3.clan()
<QuerySet [<NetworkNode: root>, <NetworkNode: a3>, <NetworkNode: b3>, <NetworkNode: c1>, <NetworkNode: c2>]>

# Get all roots or leaves associated with the node

>>> b3.get_roots()
{<NetworkNode: root>}
>>> b3.get_leaves()
{<NetworkNode: c1>, <NetworkNode: c2>}

# Perform path search

>>> root.path_ids_list(c1)
[[1, 4, 7, 9]]
>>> c1.path_ids_list(root)
Traceback (most recent call last):
  File "<input>", line 1, in <module>
    c1.path_ids_list(root)
  File "/home/runner/pgdagtest/pg/models.py", line 313, in path_ids_list
    raise NodeNotReachableException
pg.models.NodeNotReachableException
>>> c1.path_ids_list(root, directional=False)
[[1, 4, 7, 9]]
>>> root.path_ids_list(c1, max_paths=2)
[[1, 4, 7, 9], [1, 4, 8, 9]]
>>> root.shortest_path(c1)
<QuerySet [<NetworkNode: root>, <NetworkNode: a3>, <NetworkNode: b3>, <NetworkNode: c1>]>
>>> c1.shortest_path(root)
Traceback (most recent call last):
  File "<input>", line 1, in <module>
    c1.shortest_path(root)
  File "/home/runner/pgdagtest/pg/models.py", line 323, in shortest_path
    return self.filter_order_ids(self.path_ids_list(target_node, directional=directional)[0])
  File "/home/runner/pgdagtest/pg/models.py", line 313, in path_ids_list
    raise NodeNotReachableException
pg.models.NodeNotReachableException
>>> c1.shortest_path(root, directional=False)
<QuerySet [<NetworkNode: root>, <NetworkNode: a3>, <NetworkNode: b4>, <NetworkNode: c1>]>

# Get the nodes at the start or end of an edge

>>> e1.parent
<NetworkNode: root>
>>> e1.child
<NetworkNode: a1>

>>> e2.parent
<NetworkNode: b4>
>>> e2.child
<NetworkNode: c1>

# Edge-specific Manager methods

>>> NetworkEdge.objects.descendants(b3)
<QuerySet [<NetworkEdge: b3 c2>, <NetworkEdge: b3 c1>]>
>>> NetworkEdge.objects.ancestors(b3)
<QuerySet [<NetworkEdge: a3 b3>, <NetworkEdge: root a3>]>
>>> NetworkEdge.objects.clan(b3)
<QuerySet [<NetworkEdge: root a3>, <NetworkEdge: a3 b3>, <NetworkEdge: b3 c2>, <NetworkEdge: b3 c1>]>
>>> NetworkEdge.objects.shortest_path(root, c1)
<QuerySet [<NetworkEdge: root a3>, <NetworkEdge: a3 b3>, <NetworkEdge: b3 c1>]>
>>> NetworkEdge.objects.shortest_path(c1, root)
Traceback (most recent call last):
  File "<input>", line 1, in <module>
    NetworkEdge.objects.shortest_path(c1, root)
  File "/home/runner/pgdagtest/pg/models.py", line 425, in shortest_path
    self.model.objects, ["parent_id", "child_id"], start_node.path_ids_list(end_node)[0]
  File "/home/runner/pgdagtest/pg/models.py", line 313, in path_ids_list
    raise NodeNotReachableException
pg.models.NodeNotReachableException
>>> NetworkEdge.objects.shortest_path(c1, root, directional=False)
<QuerySet [<NetworkEdge: root a3>, <NetworkEdge: a3 b4>, <NetworkEdge: b4 c1>]>

Credits:

1. This excellent blog post
2. django-dag
3. django-dag-postgresql
4. django-treebeard-dag