Generate Relation Diagram from GAE ndb Model

Working with GAE, we wanted to create relation diagram from out ndb model. By deferring the rendering to dot and using Python's reflection this became an easy task.

	#!/usr/bin/env python2
	"""Export GAE model to dot format."""
	# Usage example:
	# ./ndb2dot.py cool.model | dot -Tpng -o model.png
	# Install graphviz to get the dot command line utility
	from inspect import isclass
	from os import environ
	import imp
	import sys
	# Inject GAE SDK path
	sys.path.insert(0, environ.get('GAE_PY_SDK', '/opt/google_appengine'))
	import dev_appserver # noqa
	dev_appserver.fix_sys_path()
	from google.appengine.ext import ndb # noqa
	header = '''\
	digraph G {
	graph [rankdir=LR];
	node [shape=none];
	'''
	def load_module(name):
	"""Load module from name"""
	mod = None
	for mod_name in name.split('.'):
	file, pathname, desc = imp.find_module(mod_name, mod and mod.__path__)
	mod = imp.load_module(mod_name, file, pathname, desc)
	return mod
	def models(module):
	"""Sorted list (by name) of models in module"""
	for attr in dir(module):
	obj = getattr(module, attr)
	if isclass(obj) and issubclass(obj, ndb.Model):
	yield obj
	def prop_type(prop):
	"""Property type (string)"""
	if isinstance(prop, ndb.StructuredProperty):
	return prop._modelclass.__name__
	name = prop.__class__.__name__
	suffix = 'Property'
	if name.endswith(suffix):
	name = name[:-len(suffix)]
	return name
	def model2dot(model):
	"""dot represtantation of model"""
	cls = model.__name__
	print('''\
	%s [
	label = <<table>
	<tr><td colspan="2"><b>%s</b></td></tr>''' % (cls, cls))
	links = []
	for name, prop in sorted(model._properties.iteritems()):
	if isinstance(prop, ndb.StructuredProperty):
	port = 'port="%s"' % name
	links.append((name, prop))
	else:
	port = ''
	print('%s<tr><td %s>%s</td><td>%s</td></tr>' % (
	' ' * 8, port, name, prop_type(prop)))
	print('''\
	</table>>
	];''')
	for name, prop in links:
	print(' %s:%s -> %s;' % (cls, name, prop_type(prop)))
	if __name__ == '__main__':
	from operator import attrgetter
	from argparse import ArgumentParser
	parser = ArgumentParser(description=__doc__)
	parser.add_argument('module', help='module name (e.g. "cool.model")')
	args = parser.parse_args()
	try:
	mod = load_module(args.module)
	except ImportError as err:
	raise SystemExit('error: cannot load %r - %s' % (args.module, err))
	print(header)
	for model in sorted(models(mod), key=attrgetter('__name__')):
	model2dot(model)
	print('}')

view raw ndb2dot.py hosted with ❤ by GitHub

Some links are still missing since we're using ancestor queries, but this can be handled by some class docstring syntax or just manually editing the resulting dot file.