Directed Acyclic Graph implementation for Django & Postgresql
Project description
Django & Postgresql-based Directed Acyclic Graphs
The main distinguishing factor for this project is that it can retrieve entire sections of a graph with far fewer queries than most other packages. 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. In progress are filters within the in order to limit the area of the graph to be searched.
Most Simple Example:
models.py
from django.db import models
from django_postgresql_dag.models import node_factory, edge_factory
class EdgeSet(models.Model):
name = models.CharField(max_length=100, unique=True)
def __str__(self):
return self.name
class NodeSet(models.Model):
name = models.CharField(max_length=100, unique=True)
def __str__(self):
return self.name
class NetworkEdge(edge_factory("NetworkNode", concrete=False)):
name = models.CharField(max_length=100, unique=True)
edge_set = models.ForeignKey(
EdgeSet,
on_delete=models.CASCADE,
null=True,
blank=True,
related_name="edge_set_edges",
)
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)
node_set = models.ForeignKey(
NodeSet,
on_delete=models.CASCADE,
null=True,
blank=True,
related_name="node_set_nodes",
)
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)
Add Edges and Nodes to EdgeSet and NodeSet models (FK)
>>> y = EdgeSet.objects.create()
>>> y.save()
>>> c1_ancestors = c1.ancestors_edges()
>>> for ancestor in c1_ancestors:
>>> ancestor.edge_set = y
>>> ancestor.save()
>>> x = NodeSet.objects.create()
>>> x.save()
>>> root.node_set = x
>>> root.save()
>>> a1.node_set = x
>>> a1.save()
>>> b1.node_set = x
>>> b1.save()
>>> b2.node_set = x
>>> b2.save()
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 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 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()
<QuerySet [<NetworkNode: root>, <NetworkNode: a3>, <NetworkNode: b3>, <NetworkNode: c1>, <NetworkNode: c2>]>
# Get all roots or leaves associated with the node
>>> b3.roots()
{<NetworkNode: root>}
>>> b3.leaves()
{<NetworkNode: c1>, <NetworkNode: c2>}
# Perform path search
>>> root.path(c1)
<QuerySet [<NetworkNode: root>, <NetworkNode: a3>, <NetworkNode: b3>, <NetworkNode: c1>]>
>>> c1.path(root) # Path defaults to top-down search, unless `directional` is set to False
Traceback (most recent call last):
File "<input>", line 1, in <module>
c1.path(root)
File "/home/runner/pgdagtest/pg/models.py", line 548, in path
ids = [item.id for item in self.path_raw(target_node, **kwargs)]
File "/home/runner/pgdagtest/pg/models.py", line 544, in path_raw
raise NodeNotReachableException
pg.models.NodeNotReachableException
>>> c1.path(root, directional=False)
<QuerySet [<NetworkNode: c1>, <NetworkNode: b3>, <NetworkNode: a3>, <NetworkNode: root>]>
>>> root.distance(c1)
3
# Check node properties
>>> root.is_root()
True
>>> root.is_leaf()
False
>>> root.is_island()
False
>>> c1.is_root()
False
>>> c1.is_leaf()
True
>>> c1.is_island()
False
# Get ancestors/descendants tree output
>>> a2.descendants_tree()
{<NetworkNode: b2>: {}}
>>> root.descendants_tree()
{<NetworkNode: a1>: {<NetworkNode: b1>: {}, <NetworkNode: b2>: {}}, <NetworkNode: a2>: {<NetworkNode: b2>: {}}, <NetworkNode: a3>: {<NetworkNode: b3>: {<NetworkNode: c2>: {}, <NetworkNode: c1>: {}}, <NetworkNode: b4>: <NetworkNode: c1>: {}}}}
>>> root.ancestors_tree()
{}
>>> c1.ancestors_tree()
{<NetworkNode: b3>: {<NetworkNode: a3>: {<NetworkNode: root>: {}}}, <NetworkNode: b4>: {<NetworkNode: a3>: {<NetworkNode: root>: {}}}}
>>> c2.ancestors_tree()
{<NetworkNode: b3>: {<NetworkNode: a3>: {<NetworkNode: root>: {}}}}
# Get a queryset of edges relatd to a particular node
>>> a1.ancestors_edges()
<QuerySet [<NetworkEdge: root a1>]>
>>> b4.descendants_edges()
<QuerySet [<NetworkEdge: b4 c1>]>
>>> b4.clan_edges()
<QuerySet [<NetworkEdge: root a3>, <NetworkEdge: a3 b4>, <NetworkEdge: b4 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: root a3>, <NetworkEdge: a3 b3>]>
>>> NetworkEdge.objects.clan(b3)
<QuerySet [<NetworkEdge: root a3>, <NetworkEdge: a3 b3>, <NetworkEdge: b3 c2>, <NetworkEdge: b3 c1>]>
>>> NetworkEdge.objects.path(root, c1)
<QuerySet [<NetworkEdge: root a3>, <NetworkEdge: a3 b3>, <NetworkEdge: b3 c1>]>
>>> NetworkEdge.objects.path(c1, root) # Path defaults to top-down search, unless `directional` is set to False
Traceback (most recent call last):
File "<input>", line 1, in <module>
NetworkEdge.objects.path(c1, root)
File "/home/runner/pgdagtest/pg/models.py", line 677, in path
start_node.path(end_node),
File "/home/runner/pgdagtest/pg/models.py", line 548, in path
ids = [item.id for item in self.path_raw(target_node, **kwargs)]
File "/home/runner/pgdagtest/pg/models.py", line 544, in path_raw
raise NodeNotReachableException
pg.models.NodeNotReachableException
>>> NetworkEdge.objects.path(c1, root, directional=False)
<QuerySet [<NetworkEdge: b3 c1>, <NetworkEdge: a3 b3>, <NetworkEdge: root a3>]>
ToDo
- Describe methods of filtering nodes and edges within the CTE.
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