Added contrib tools with conversion to networkx, this is useful for visualising schema - like in the README

Author: moagstar

README.md

@@ -70,3 +70,7 @@ schemas common in OLAP. For example when the same table is the target of
 multiple foreign keys the basic functionality of SQLAlchemy breaks down.
 Also since you might have sub-queries or CTEs which you might want to
 attach to your schema it's not always possible to use foreign keys.
+
+TODO: standard schema diagram, explain difference
+
+![star schema](doc/sales_schema.png "example star schema")

doc/sales_schema.png

@@ -17,6 +17,7 @@ sqlalchemy-stubs = "^0.3"
 pycodestyle = "^2.6.0"
 mistletoe = "^0.7.2"
 beautifulsoup4 = "^4.9.3"
+networkx = "^2.5"
 
 [build-system]
 requires = ["poetry>=0.12"]

poetry.lock

@@ -1,5 +1,8 @@
 [mypy]
 plugins = sqlmypy
 
+[mypy-networkx.*]
+ignore_missing_imports = True
+
 [pycodestyle]
 max-line-length = 100

pyproject.toml

@@ -0,0 +1,20 @@
+import networkx as nx
+
+from star_alchemy import StarSchema
+
+
+def to_nx(star_schema: StarSchema):
+    """
+
+    :param star_schema:
+
+    :return:
+    """
+    G = nx.DiGraph()
+
+    for s in star_schema:
+        G.add_node(s.name, name=str(s.name))
+        if s.parent is not None:
+            G.add_edge(s.parent.name, s.name)
+
+    return G

setup.cfg

@@ -0,0 +1,48 @@
+import difflib
+import json
+from unittest import TestCase
+
+import networkx as nx
+
+from examples.sales import schema
+from star_alchemy.contrib.networkx import to_nx
+
+
+class ToNxTestCase(TestCase):
+
+    def test_to_nx(self):
+        G = to_nx(schema)
+        actual = json.dumps(nx.tree_data(G, schema.name), indent=4)
+        expected = json.dumps(indent=4, obj={
+            'name': 'sale',
+            'id': 'sale',
+            'children': [
+                {
+                    'name': 'product',
+                    'id': 'product',
+                    'children': [
+                        {'name': 'category', 'id': 'category'}
+                    ]
+                },
+                {
+                    'name': 'employee',
+                    'id': 'employee',
+                    'children': [
+                        {'name': 'department', 'id': 'department'},
+                        {'name': 'employee_location', 'id': 'employee_location'}
+                    ]
+                },
+                {
+                    'name': 'customer',
+                    'id': 'customer',
+                    'children': [
+                        {'name': 'customer_location', 'id': 'customer_location'}
+                    ]
+                }
+            ]
+        })
+        if actual != expected:
+            actual_lines = actual.split('\n')
+            expected_lines = expected.split('\n')
+            diff = difflib.unified_diff(actual_lines, expected_lines)
+            self.fail('\n'.join(diff))

star_alchemy/contrib/__init__.py

@@ -211,6 +211,8 @@ class DocStringTestCase(TestCase, DocTestMixin(_star_alchemy)):
 
     Most docstring checking focus on the format, which is less important
     for me.
+
+    TODO: Make this more generic with auto-discovery
     """
 
     @property