Fixed #22861: Internal migrations done first so __first__ works

Thanks to Chris Beaven.

django/db/migrations/graph.py

@@ -74,7 +74,7 @@ class MigrationGraph(object):
         for node in self.nodes:
             if not any(key[0] == node[0] for key in self.dependencies.get(node, set())) and (not app or app == node[0]):
                 roots.add(node)
-        return roots
+        return sorted(roots)
 
     def leaf_nodes(self, app=None):
         """
@@ -88,7 +88,7 @@ class MigrationGraph(object):
         for node in self.nodes:
             if not any(key[0] == node[0] for key in self.dependents.get(node, set())) and (not app or app == node[0]):
                 leaves.add(node)
-        return leaves
+        return sorted(leaves)
 
     def dfs(self, start, get_children):
         """

django/db/migrations/loader.py

@@ -223,8 +223,19 @@ class MigrationLoader(object):
         self.graph = MigrationGraph()
         for key, migration in normal.items():
             self.graph.add_node(key, migration)
+        # Add all internal dependencies first to ensure __first__ dependencies
+        # find the correct root node.
         for key, migration in normal.items():
             for parent in migration.dependencies:
+                if parent[0] != key[0] or parent[1] == '__first__':
+                    # Ignore __first__ references to the same app (#22325)
+                    continue
+                self.graph.add_dependency(key, parent)
+        for key, migration in normal.items():
+            for parent in migration.dependencies:
+                if parent[0] == key[0]:
+                    # Internal dependencies already added.
+                    continue
                 parent = self.check_key(parent, key[0])
                 if parent is not None:
                     self.graph.add_dependency(key, parent)

tests/migrations/test_graph.py

@@ -51,11 +51,11 @@ class GraphTests(TestCase):
         # Test roots and leaves
         self.assertEqual(
             graph.root_nodes(),
-            set([('app_a', '0001'), ('app_b', '0001')]),
+            [('app_a', '0001'), ('app_b', '0001')],
         )
         self.assertEqual(
             graph.leaf_nodes(),
-            set([('app_a', '0004'), ('app_b', '0002')]),
+            [('app_a', '0004'), ('app_b', '0002')],
         )
 
     def test_complex_graph(self):
@@ -105,11 +105,11 @@ class GraphTests(TestCase):
         # Test roots and leaves
         self.assertEqual(
             graph.root_nodes(),
-            set([('app_a', '0001'), ('app_b', '0001'), ('app_c', '0001')]),
+            [('app_a', '0001'), ('app_b', '0001'), ('app_c', '0001')],
         )
         self.assertEqual(
             graph.leaf_nodes(),
-            set([('app_a', '0004'), ('app_b', '0002'), ('app_c', '0002')]),
+            [('app_a', '0004'), ('app_b', '0002'), ('app_c', '0002')],
         )
 
     def test_circular_graph(self):

tests/migrations/test_loader.py

@@ -142,6 +142,26 @@ class LoaderTests(TestCase):
             ],
         )
 
+    @override_settings(MIGRATION_MODULES={
+        "migrations": "migrations.test_migrations_first",
+        "migrations2": "migrations2.test_migrations_2_first",
+    })
+    @modify_settings(INSTALLED_APPS={'append': 'migrations2'})
+    def test_first(self):
+        """
+        Makes sure the '__first__' migrations build correctly.
+        """
+        migration_loader = MigrationLoader(connection)
+        self.assertEqual(
+            migration_loader.graph.forwards_plan(("migrations", "second")),
+            [
+                ("migrations", "thefirst"),
+                ("migrations2", "0001_initial"),
+                ("migrations2", "0002_second"),
+                ("migrations", "second"),
+            ],
+        )
+
     @override_settings(MIGRATION_MODULES={"migrations": "migrations.test_migrations"})
     def test_name_match(self):
         "Tests prefix name matching"

tests/migrations/test_migrations_first/second.py

@@ -0,0 +1,30 @@
+# -*- coding: utf-8 -*-
+from __future__ import unicode_literals
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ("migrations", "thefirst"),
+        ("migrations2", "0002_second"),
+    ]
+
+    operations = [
+
+        migrations.DeleteModel("Tribble"),
+
+        migrations.RemoveField("Author", "silly_field"),
+
+        migrations.AddField("Author", "rating", models.IntegerField(default=0)),
+
+        migrations.CreateModel(
+            "Book",
+            [
+                ("id", models.AutoField(primary_key=True)),
+                ("author", models.ForeignKey("migrations.Author", null=True)),
+            ],
+        )
+
+    ]

tests/migrations/test_migrations_first/thefirst.py

@@ -0,0 +1,30 @@
+# -*- coding: utf-8 -*-
+from __future__ import unicode_literals
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    operations = [
+
+        migrations.CreateModel(
+            "Author",
+            [
+                ("id", models.AutoField(primary_key=True)),
+                ("name", models.CharField(max_length=255)),
+                ("slug", models.SlugField(null=True)),
+                ("age", models.IntegerField(default=0)),
+                ("silly_field", models.BooleanField(default=False)),
+            ],
+        ),
+
+        migrations.CreateModel(
+            "Tribble",
+            [
+                ("id", models.AutoField(primary_key=True)),
+                ("fluffy", models.BooleanField(default=True)),
+            ],
+        )
+
+    ]

tests/migrations2/test_migrations_2_first/0001_initial.py

@@ -0,0 +1,26 @@
+# -*- coding: utf-8 -*-
+from __future__ import unicode_literals
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ("migrations", "__first__"),
+    ]
+
+    operations = [
+
+        migrations.CreateModel(
+            "OtherAuthor",
+            [
+                ("id", models.AutoField(primary_key=True)),
+                ("name", models.CharField(max_length=255)),
+                ("slug", models.SlugField(null=True)),
+                ("age", models.IntegerField(default=0)),
+                ("silly_field", models.BooleanField(default=False)),
+            ],
+        ),
+
+    ]

tests/migrations2/test_migrations_2_first/0002_second.py

@@ -0,0 +1,22 @@
+# -*- coding: utf-8 -*-
+from __future__ import unicode_literals
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [("migrations2", "0001_initial")]
+
+    operations = [
+
+        migrations.CreateModel(
+            "Bookstore",
+            [
+                ("id", models.AutoField(primary_key=True)),
+                ("name", models.CharField(max_length=255)),
+                ("slug", models.SlugField(null=True)),
+            ],
+        ),
+
+    ]