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Adding a dependency graph class and tests

This commit is contained in:
Andrew Godwin 2013-05-10 12:52:04 +01:00
parent 75bf394d86
commit f6801a234f
6 changed files with 224 additions and 0 deletions
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0
django/db/migrations/__init__.py Normal file
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96
django/db/migrations/graph.py Normal file
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@ -0,0 +1,96 @@
from django.utils.datastructures import SortedSet
class MigrationsGraph(object):
"""
Represents the digraph of all migrations in a project.
Each migration is a node, and each dependency is an edge. There are
no implicit dependencies between numbered migrations - the numbering is
merely a convention to aid file listing. Every new numbered migration
has a declared dependency to the previous number, meaning that VCS
branch merges can be detected and resolved.
Migrations files can be marked as replacing another set of migrations -
this is to support the "squash" feature. The graph handler isn't resposible
for these; instead, the code to load them in here should examine the
migration files and if the replaced migrations are all either unapplied
or not present, it should ignore the replaced ones, load in just the
replacing migration, and repoint any dependencies that pointed to the
replaced migrations to point to the replacing one.
A node should be a tuple: (applabel, migration_name) - but the code
here doesn't really care.
"""
def __init__(self):
self.nodes = {}
self.dependencies = {}
self.dependents = {}
def add_node(self, node, implementation):
self.nodes[node] = implementation
def add_dependency(self, child, parent):
self.nodes[child] = None
self.nodes[parent] = None
self.dependencies.setdefault(child, set()).add(parent)
self.dependents.setdefault(parent, set()).add(child)
def forwards_plan(self, node):
"""
Given a node, returns a list of which previous nodes (dependencies)
must be applied, ending with the node itself.
This is the list you would follow if applying the migrations to
a database.
"""
if node not in self.nodes:
raise ValueError("Node %r not a valid node" % node)
return self.dfs(node, lambda x: self.dependencies.get(x, set()))
def backwards_plan(self, node):
"""
Given a node, returns a list of which dependent nodes (dependencies)
must be unapplied, ending with the node itself.
This is the list you would follow if removing the migrations from
a database.
"""
if node not in self.nodes:
raise ValueError("Node %r not a valid node" % node)
return self.dfs(node, lambda x: self.dependents.get(x, set()))
def dfs(self, start, get_children):
"""
Dynamic programming based depth first search, for finding dependencies.
"""
cache = {}
def _dfs(start, get_children, path):
# If we already computed this, use that (dynamic programming)
if (start, get_children) in cache:
return cache[(start, get_children)]
# If we've traversed here before, that's a circular dep
if start in path:
raise CircularDependencyException(path[path.index(start):] + [start])
# Build our own results list, starting with us
results = []
results.append(start)
# We need to add to results all the migrations this one depends on
children = sorted(get_children(start))
path.append(start)
for n in children:
results = _dfs(n, get_children, path) + results
path.pop()
# Use SortedSet to ensure only one instance of each result
results = list(SortedSet(results))
# Populate DP cache
cache[(start, get_children)] = results
# Done!
return results
return _dfs(start, get_children, [])
class CircularDependencyException(Exception):
"""
Raised when there's an impossible-to-resolve circular dependency.
"""
pass

30
django/utils/datastructures.py
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@ -252,6 +252,36 @@ class SortedDict(dict):
super(SortedDict, self).clear()
self.keyOrder = []
class SortedSet(object):
"""
A set which keeps the ordering of the inserted items.
Currently backs onto SortedDict.
"""
def __init__(self, iterable=None):
self.dict = SortedDict(((x, None) for x in iterable) if iterable else [])
def add(self, item):
self.dict[item] = None
def remove(self, item):
del self.dict[item]
def discard(self, item):
try:
self.remove(item)
except KeyError:
pass
def __iter__(self):
return iter(self.dict.keys())
def __contains__(self, item):
return item in self.dict
def __nonzero__(self):
return bool(self.dict)
class MultiValueDictKeyError(KeyError):
pass

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tests/migrations/__init__.py Normal file
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tests/migrations/models.py Normal file
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98
tests/migrations/tests.py Normal file
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from django.test import TransactionTestCase
from django.db.migrations.graph import MigrationsGraph, CircularDependencyException
class GraphTests(TransactionTestCase):
"""
Tests the digraph structure.
"""
def test_simple_graph(self):
"""
Tests a basic dependency graph:
app_a: 0001 <-- 0002 <--- 0003 <-- 0004
/
app_b: 0001 <-- 0002 <-/
"""
# Build graph
graph = MigrationsGraph()
graph.add_dependency(("app_a", "0004"), ("app_a", "0003"))
graph.add_dependency(("app_a", "0003"), ("app_a", "0002"))
graph.add_dependency(("app_a", "0002"), ("app_a", "0001"))
graph.add_dependency(("app_a", "0003"), ("app_b", "0002"))
graph.add_dependency(("app_b", "0002"), ("app_b", "0001"))
# Test root migration case
self.assertEqual(
graph.forwards_plan(("app_a", "0001")),
[('app_a', '0001')],
)
# Test branch B only
self.assertEqual(
graph.forwards_plan(("app_b", "0002")),
[("app_b", "0001"), ("app_b", "0002")],
)
# Test whole graph
self.assertEqual(
graph.forwards_plan(("app_a", "0004")),
[('app_b', '0001'), ('app_b', '0002'), ('app_a', '0001'), ('app_a', '0002'), ('app_a', '0003'), ('app_a', '0004')],
)
# Test reverse to b:0002
self.assertEqual(
graph.backwards_plan(("app_b", "0002")),
[('app_a', '0004'), ('app_a', '0003'), ('app_b', '0002')],
)
def test_complex_graph(self):
"""
Tests a complex dependency graph:
app_a: 0001 <-- 0002 <--- 0003 <-- 0004
\ \ / /
app_b: 0001 <-\ 0002 <-X /
\ \ /
app_c: \ 0001 <-- 0002 <-
"""
# Build graph
graph = MigrationsGraph()
graph.add_dependency(("app_a", "0004"), ("app_a", "0003"))
graph.add_dependency(("app_a", "0003"), ("app_a", "0002"))
graph.add_dependency(("app_a", "0002"), ("app_a", "0001"))
graph.add_dependency(("app_a", "0003"), ("app_b", "0002"))
graph.add_dependency(("app_b", "0002"), ("app_b", "0001"))
graph.add_dependency(("app_a", "0004"), ("app_c", "0002"))
graph.add_dependency(("app_c", "0002"), ("app_c", "0001"))
graph.add_dependency(("app_c", "0001"), ("app_b", "0001"))
graph.add_dependency(("app_c", "0002"), ("app_a", "0002"))
# Test branch C only
self.assertEqual(
graph.forwards_plan(("app_c", "0002")),
[('app_b', '0001'), ('app_c', '0001'), ('app_a', '0001'), ('app_a', '0002'), ('app_c', '0002')],
)
# Test whole graph
self.assertEqual(
graph.forwards_plan(("app_a", "0004")),
[('app_b', '0001'), ('app_c', '0001'), ('app_a', '0001'), ('app_a', '0002'), ('app_c', '0002'), ('app_b', '0002'), ('app_a', '0003'), ('app_a', '0004')],
)
# Test reverse to b:0001
self.assertEqual(
graph.backwards_plan(("app_b", "0001")),
[('app_a', '0004'), ('app_c', '0002'), ('app_c', '0001'), ('app_a', '0003'), ('app_b', '0002'), ('app_b', '0001')],
)
def test_circular_graph(self):
"""
Tests a circular dependency graph.
"""
# Build graph
graph = MigrationsGraph()
graph.add_dependency(("app_a", "0003"), ("app_a", "0002"))
graph.add_dependency(("app_a", "0002"), ("app_a", "0001"))
graph.add_dependency(("app_a", "0001"), ("app_b", "0002"))
graph.add_dependency(("app_b", "0002"), ("app_b", "0001"))
graph.add_dependency(("app_b", "0001"), ("app_a", "0003"))
# Test whole graph
self.assertRaises(
CircularDependencyException,
graph.forwards_plan, ("app_a", "0003"),
)