django/tests/migrations/test_graph.py

from django.test import TestCase
from django.db.migrations.graph import MigrationGraph, CircularDependencyError


class GraphTests(TestCase):
    """
    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 = MigrationGraph()
        graph.add_node(("app_a", "0001"), None)
        graph.add_node(("app_a", "0002"), None)
        graph.add_node(("app_a", "0003"), None)
        graph.add_node(("app_a", "0004"), None)
        graph.add_node(("app_b", "0001"), None)
        graph.add_node(("app_b", "0002"), None)
        graph.add_dependency("app_a.0004", ("app_a", "0004"), ("app_a", "0003"))
        graph.add_dependency("app_a.0003", ("app_a", "0003"), ("app_a", "0002"))
        graph.add_dependency("app_a.0002", ("app_a", "0002"), ("app_a", "0001"))
        graph.add_dependency("app_a.0003", ("app_a", "0003"), ("app_b", "0002"))
        graph.add_dependency("app_b.0002", ("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')],
        )
        # Test roots and leaves
        self.assertEqual(
            graph.root_nodes(),
            [('app_a', '0001'), ('app_b', '0001')],
        )
        self.assertEqual(
            graph.leaf_nodes(),
            [('app_a', '0004'), ('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 = MigrationGraph()
        graph.add_node(("app_a", "0001"), None)
        graph.add_node(("app_a", "0002"), None)
        graph.add_node(("app_a", "0003"), None)
        graph.add_node(("app_a", "0004"), None)
        graph.add_node(("app_b", "0001"), None)
        graph.add_node(("app_b", "0002"), None)
        graph.add_node(("app_c", "0001"), None)
        graph.add_node(("app_c", "0002"), None)
        graph.add_dependency("app_a.0004", ("app_a", "0004"), ("app_a", "0003"))
        graph.add_dependency("app_a.0003", ("app_a", "0003"), ("app_a", "0002"))
        graph.add_dependency("app_a.0002", ("app_a", "0002"), ("app_a", "0001"))
        graph.add_dependency("app_a.0003", ("app_a", "0003"), ("app_b", "0002"))
        graph.add_dependency("app_b.0002", ("app_b", "0002"), ("app_b", "0001"))
        graph.add_dependency("app_a.0004", ("app_a", "0004"), ("app_c", "0002"))
        graph.add_dependency("app_c.0002", ("app_c", "0002"), ("app_c", "0001"))
        graph.add_dependency("app_c.0001", ("app_c", "0001"), ("app_b", "0001"))
        graph.add_dependency("app_c.0002", ("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')],
        )
        # Test roots and leaves
        self.assertEqual(
            graph.root_nodes(),
            [('app_a', '0001'), ('app_b', '0001'), ('app_c', '0001')],
        )
        self.assertEqual(
            graph.leaf_nodes(),
            [('app_a', '0004'), ('app_b', '0002'), ('app_c', '0002')],
        )

    def test_circular_graph(self):
        """
        Tests a circular dependency graph.
        """
        # Build graph
        graph = MigrationGraph()
        graph.add_node(("app_a", "0001"), None)
        graph.add_node(("app_a", "0002"), None)
        graph.add_node(("app_a", "0003"), None)
        graph.add_node(("app_b", "0001"), None)
        graph.add_node(("app_b", "0002"), None)
        graph.add_dependency("app_a.0003", ("app_a", "0003"), ("app_a", "0002"))
        graph.add_dependency("app_a.0002", ("app_a", "0002"), ("app_a", "0001"))
        graph.add_dependency("app_a.0001", ("app_a", "0001"), ("app_b", "0002"))
        graph.add_dependency("app_b.0002", ("app_b", "0002"), ("app_b", "0001"))
        graph.add_dependency("app_b.0001", ("app_b", "0001"), ("app_a", "0003"))
        # Test whole graph
        self.assertRaises(
            CircularDependencyError,
            graph.forwards_plan, ("app_a", "0003"),
        )

    def test_dfs(self):
        graph = MigrationGraph()
        root = ("app_a", "1")
        graph.add_node(root, None)
        expected = [root]
        for i in range(2, 1000):
            parent = ("app_a", str(i - 1))
            child = ("app_a", str(i))
            graph.add_node(child, None)
            graph.add_dependency(str(i), child, parent)
            expected.append(child)

        actual = graph.dfs(root, lambda x: graph.dependents.get(x, set()))
        self.assertEqual(expected[::-1], actual)

    def test_plan_invalid_node(self):
        """
        Tests for forwards/backwards_plan of nonexistent node.
        """
        graph = MigrationGraph()
        message = "Node ('app_b', '0001') not a valid node"

        with self.assertRaisesMessage(ValueError, message):
            graph.forwards_plan(("app_b", "0001"))

        with self.assertRaisesMessage(ValueError, message):
            graph.backwards_plan(("app_b", "0001"))

    def test_missing_parent_nodes(self):
        """
        Tests for missing parent nodes.
        """
        # Build graph
        graph = MigrationGraph()
        graph.add_node(("app_a", "0001"), None)
        graph.add_node(("app_a", "0002"), None)
        graph.add_node(("app_a", "0003"), None)
        graph.add_node(("app_b", "0001"), None)
        graph.add_dependency("app_a.0003", ("app_a", "0003"), ("app_a", "0002"))
        graph.add_dependency("app_a.0002", ("app_a", "0002"), ("app_a", "0001"))
        msg = "Migration app_a.0001 dependencies reference nonexistent parent node ('app_b', '0002')"
        with self.assertRaisesMessage(KeyError, msg):
            graph.add_dependency("app_a.0001", ("app_a", "0001"), ("app_b", "0002"))

    def test_missing_child_nodes(self):
        """
        Tests for missing child nodes.
        """
        # Build graph
        graph = MigrationGraph()
        graph.add_node(("app_a", "0001"), None)
        msg = "Migration app_a.0002 dependencies reference nonexistent child node ('app_a', '0002')"
        with self.assertRaisesMessage(KeyError, msg):
            graph.add_dependency("app_a.0002", ("app_a", "0002"), ("app_a", "0001"))