Fixed #31468 -- Allowed specifying migration filename in Operation.

This adds also suggested filename for many built-in operations.

10 files changed, 149 insertions, 13 deletions

diff --git a/django/contrib/postgres/operations.py b/django/contrib/postgres/operations.py
index 740911d059..b25438b826 100644
--- a/django/contrib/postgres/operations.py
+++ b/django/contrib/postgres/operations.py
@@ -55,6 +55,10 @@ class CreateExtension(Operation):
     def describe(self):
         return "Creates extension %s" % self.name
 
+    @property
+    def migration_name_fragment(self):
+        return 'create_extension_%s' % self.name
+
 
 class BloomExtension(CreateExtension):
 
diff --git a/django/db/migrations/autodetector.py b/django/db/migrations/autodetector.py
index 85c3013897..a6edc2cd6e 100644
--- a/django/db/migrations/autodetector.py
+++ b/django/db/migrations/autodetector.py
@@ -1313,19 +1313,14 @@ class MigrationAutodetector:
         represent. Names are not guaranteed to be unique, but put some effort
         into the fallback name to avoid VCS conflicts if possible.
         """
+        name = None
         if len(ops) == 1:
-            if isinstance(ops[0], operations.CreateModel):
-                return ops[0].name_lower
-            elif isinstance(ops[0], operations.DeleteModel):
-                return "delete_%s" % ops[0].name_lower
-            elif isinstance(ops[0], operations.AddField):
-                return "%s_%s" % (ops[0].model_name_lower, ops[0].name_lower)
-            elif isinstance(ops[0], operations.RemoveField):
-                return "remove_%s_%s" % (ops[0].model_name_lower, ops[0].name_lower)
-        elif ops:
-            if all(isinstance(o, operations.CreateModel) for o in ops):
-                return "_".join(sorted(o.name_lower for o in ops))
-        return "auto_%s" % get_migration_name_timestamp()
+            name = ops[0].migration_name_fragment
+        elif len(ops) > 1 and all(isinstance(o, operations.CreateModel) for o in ops):
+            name = '_'.join(sorted(o.migration_name_fragment for o in ops))
+        if name is None:
+            name = 'auto_%s' % get_migration_name_timestamp()
+        return name
 
     @classmethod
     def parse_number(cls, name):
diff --git a/django/db/migrations/operations/base.py b/django/db/migrations/operations/base.py
index 35fdd72310..18935520f8 100644
--- a/django/db/migrations/operations/base.py
+++ b/django/db/migrations/operations/base.py
@@ -79,6 +79,14 @@ class Operation:
         """
         return "%s: %s" % (self.__class__.__name__, self._constructor_args)
 
+    @property
+    def migration_name_fragment(self):
+        """
+        A filename part suitable for automatically naming a migration
+        containing this operation, or None if not applicable.
+        """
+        return None
+
     def references_model(self, name, app_label):
         """
         Return True if there is a chance this operation references the given
diff --git a/django/db/migrations/operations/fields.py b/django/db/migrations/operations/fields.py
index e4f78e365e..8e494fd595 100644
--- a/django/db/migrations/operations/fields.py
+++ b/django/db/migrations/operations/fields.py
@@ -116,6 +116,10 @@ class AddField(FieldOperation):
     def describe(self):
         return "Add field %s to %s" % (self.name, self.model_name)
 
+    @property
+    def migration_name_fragment(self):
+        return '%s_%s' % (self.model_name_lower, self.name_lower)
+
     def reduce(self, operation, app_label):
         if isinstance(operation, FieldOperation) and self.is_same_field_operation(operation):
             if isinstance(operation, AlterField):
@@ -174,6 +178,10 @@ class RemoveField(FieldOperation):
     def describe(self):
         return "Remove field %s from %s" % (self.name, self.model_name)
 
+    @property
+    def migration_name_fragment(self):
+        return 'remove_%s_%s' % (self.model_name_lower, self.name_lower)
+
     def reduce(self, operation, app_label):
         from .models import DeleteModel
         if isinstance(operation, DeleteModel) and operation.name_lower == self.model_name_lower:
@@ -243,6 +251,10 @@ class AlterField(FieldOperation):
     def describe(self):
         return "Alter field %s on %s" % (self.name, self.model_name)
 
+    @property
+    def migration_name_fragment(self):
+        return 'alter_%s_%s' % (self.model_name_lower, self.name_lower)
+
     def reduce(self, operation, app_label):
         if isinstance(operation, RemoveField) and self.is_same_field_operation(operation):
             return [operation]
@@ -354,6 +366,14 @@ class RenameField(FieldOperation):
     def describe(self):
         return "Rename field %s on %s to %s" % (self.old_name, self.model_name, self.new_name)
 
+    @property
+    def migration_name_fragment(self):
+        return 'rename_%s_%s_%s' % (
+            self.old_name_lower,
+            self.model_name_lower,
+            self.new_name_lower,
+        )
+
     def references_field(self, model_name, name, app_label):
         return self.references_model(model_name, app_label) and (
             name.lower() == self.old_name_lower or
diff --git a/django/db/migrations/operations/models.py b/django/db/migrations/operations/models.py
index 8c06c4d157..dddf7c679c 100644
--- a/django/db/migrations/operations/models.py
+++ b/django/db/migrations/operations/models.py
@@ -99,6 +99,10 @@ class CreateModel(ModelOperation):
     def describe(self):
         return "Create %smodel %s" % ("proxy " if self.options.get("proxy", False) else "", self.name)
 
+    @property
+    def migration_name_fragment(self):
+        return self.name_lower
+
     def references_model(self, name, app_label):
         name_lower = name.lower()
         if name_lower == self.name_lower:
@@ -273,6 +277,10 @@ class DeleteModel(ModelOperation):
     def describe(self):
         return "Delete model %s" % self.name
 
+    @property
+    def migration_name_fragment(self):
+        return 'delete_%s' % self.name_lower
+
 
 class RenameModel(ModelOperation):
     """Rename a model."""
@@ -397,6 +405,10 @@ class RenameModel(ModelOperation):
     def describe(self):
         return "Rename model %s to %s" % (self.old_name, self.new_name)
 
+    @property
+    def migration_name_fragment(self):
+        return 'rename_%s_%s' % (self.old_name_lower, self.new_name_lower)
+
     def reduce(self, operation, app_label):
         if (isinstance(operation, RenameModel) and
                 self.new_name_lower == operation.old_name_lower):
@@ -470,6 +482,10 @@ class AlterModelTable(ModelOptionOperation):
             self.table if self.table is not None else "(default)"
         )
 
+    @property
+    def migration_name_fragment(self):
+        return 'alter_%s_table' % self.name_lower
+
 
 class AlterTogetherOptionOperation(ModelOptionOperation):
     option_name = None
@@ -526,6 +542,10 @@ class AlterTogetherOptionOperation(ModelOptionOperation):
     def describe(self):
         return "Alter %s for %s (%s constraint(s))" % (self.option_name, self.name, len(self.option_value or ''))
 
+    @property
+    def migration_name_fragment(self):
+        return 'alter_%s_%s' % (self.name_lower, self.option_name)
+
 
 class AlterUniqueTogether(AlterTogetherOptionOperation):
     """
@@ -607,6 +627,10 @@ class AlterOrderWithRespectTo(ModelOptionOperation):
     def describe(self):
         return "Set order_with_respect_to on %s to %s" % (self.name, self.order_with_respect_to)
 
+    @property
+    def migration_name_fragment(self):
+        return 'alter_%s_order_with_respect_to' % self.name_lower
+
 
 class AlterModelOptions(ModelOptionOperation):
     """
@@ -662,6 +686,10 @@ class AlterModelOptions(ModelOptionOperation):
     def describe(self):
         return "Change Meta options on %s" % self.name
 
+    @property
+    def migration_name_fragment(self):
+        return 'alter_%s_options' % self.name_lower
+
 
 class AlterModelManagers(ModelOptionOperation):
     """Alter the model's managers."""
@@ -693,6 +721,10 @@ class AlterModelManagers(ModelOptionOperation):
     def describe(self):
         return "Change managers on %s" % self.name
 
+    @property
+    def migration_name_fragment(self):
+        return 'alter_%s_managers' % self.name_lower
+
 
 class IndexOperation(Operation):
     option_name = 'indexes'
@@ -747,6 +779,10 @@ class AddIndex(IndexOperation):
             self.model_name,
         )
 
+    @property
+    def migration_name_fragment(self):
+        return '%s_%s' % (self.model_name_lower, self.index.name.lower())
+
 
 class RemoveIndex(IndexOperation):
     """Remove an index from a model."""
@@ -789,6 +825,10 @@ class RemoveIndex(IndexOperation):
     def describe(self):
         return 'Remove index %s from %s' % (self.name, self.model_name)
 
+    @property
+    def migration_name_fragment(self):
+        return 'remove_%s_%s' % (self.model_name_lower, self.name.lower())
+
 
 class AddConstraint(IndexOperation):
     option_name = 'constraints'
@@ -821,6 +861,10 @@ class AddConstraint(IndexOperation):
     def describe(self):
         return 'Create constraint %s on model %s' % (self.constraint.name, self.model_name)
 
+    @property
+    def migration_name_fragment(self):
+        return '%s_%s' % (self.model_name_lower, self.constraint.name.lower())
+
 
 class RemoveConstraint(IndexOperation):
     option_name = 'constraints'
@@ -857,3 +901,7 @@ class RemoveConstraint(IndexOperation):
 
     def describe(self):
         return 'Remove constraint %s from model %s' % (self.name, self.model_name)
+
+    @property
+    def migration_name_fragment(self):
+        return 'remove_%s_%s' % (self.model_name_lower, self.name.lower())
diff --git a/docs/ref/migration-operations.txt b/docs/ref/migration-operations.txt
index a6b42bdc99..d1620cce8e 100644
--- a/docs/ref/migration-operations.txt
+++ b/docs/ref/migration-operations.txt
@@ -484,6 +484,16 @@ structure of an ``Operation`` looks like this::
             # This is used to describe what the operation does in console output.
             return "Custom Operation"
 
+        @property
+        def migration_name_fragment(self):
+            # Optional. A filename part suitable for automatically naming a
+            # migration containing this operation, or None if not applicable.
+            return "custom_operation_%s_%s" % (self.arg1, self.arg2)
+
+.. versionadded:: 3.2
+
+    The ``migration_name_fragment`` property was added.
+
 You can take this template and work from it, though we suggest looking at the
 built-in Django operations in ``django.db.migrations.operations`` - they cover
 a lot of the example usage of semi-internal aspects of the migration framework
@@ -553,3 +563,7 @@ state changes, all it does is run one command::
 
         def describe(self):
             return "Creates extension %s" % self.name
+
+        @property
+        def migration_name_fragment(self):
+            return "create_extension_%s" % self.name
diff --git a/docs/releases/3.2.txt b/docs/releases/3.2.txt
index 1ba636c4a6..a869eb49cf 100644
--- a/docs/releases/3.2.txt
+++ b/docs/releases/3.2.txt
@@ -171,7 +171,9 @@ Management Commands
 Migrations
 ~~~~~~~~~~
 
-* ...
+* The new ``Operation.migration_name_fragment`` property allows providing a
+  filename fragment that will be used to name a migration containing only that
+  operation.
 
 Models
 ~~~~~~
diff --git a/tests/migrations/test_autodetector.py b/tests/migrations/test_autodetector.py
index 52d8e305ce..ab52b8116d 100644
--- a/tests/migrations/test_autodetector.py
+++ b/tests/migrations/test_autodetector.py
@@ -2495,6 +2495,11 @@ class AutodetectorSuggestNameTests(SimpleTestCase):
         ]
         self.assertEqual(MigrationAutodetector.suggest_name(ops), 'animal_person')
 
+    def test_none_name(self):
+        ops = [migrations.RunSQL('SELECT 1 FROM person;')]
+        suggest_name = MigrationAutodetector.suggest_name(ops)
+        self.assertIs(suggest_name.startswith('auto_'), True)
+
     def test_auto(self):
         suggest_name = MigrationAutodetector.suggest_name([])
         self.assertIs(suggest_name.startswith('auto_'), True)
diff --git a/tests/migrations/test_operations.py b/tests/migrations/test_operations.py
index e985535679..855a052058 100644
--- a/tests/migrations/test_operations.py
+++ b/tests/migrations/test_operations.py
@@ -36,6 +36,7 @@ class OperationTests(OperationTestBase):
             ],
         )
         self.assertEqual(operation.describe(), "Create model Pony")
+        self.assertEqual(operation.migration_name_fragment, 'pony')
         # Test the state alteration
         project_state = ProjectState()
         new_state = project_state.clone()
@@ -486,6 +487,7 @@ class OperationTests(OperationTestBase):
         # Test the state alteration
         operation = migrations.DeleteModel("Pony")
         self.assertEqual(operation.describe(), "Delete model Pony")
+        self.assertEqual(operation.migration_name_fragment, 'delete_pony')
         new_state = project_state.clone()
         operation.state_forwards("test_dlmo", new_state)
         self.assertNotIn(("test_dlmo", "pony"), new_state.models)
@@ -559,6 +561,7 @@ class OperationTests(OperationTestBase):
         # Test the state alteration
         operation = migrations.RenameModel("Pony", "Horse")
         self.assertEqual(operation.describe(), "Rename model Pony to Horse")
+        self.assertEqual(operation.migration_name_fragment, 'rename_pony_horse')
         # Test initial state and database
         self.assertIn(("test_rnmo", "pony"), project_state.models)
         self.assertNotIn(("test_rnmo", "horse"), project_state.models)
@@ -855,6 +858,7 @@ class OperationTests(OperationTestBase):
             models.FloatField(null=True, default=5),
         )
         self.assertEqual(operation.describe(), "Add field height to Pony")
+        self.assertEqual(operation.migration_name_fragment, 'pony_height')
         project_state, new_state = self.make_test_state("test_adfl", operation)
         self.assertEqual(len(new_state.models["test_adfl", "pony"].fields), 4)
         field = new_state.models['test_adfl', 'pony'].fields['height']
@@ -1155,6 +1159,7 @@ class OperationTests(OperationTestBase):
         # Test the state alteration
         operation = migrations.RemoveField("Pony", "pink")
         self.assertEqual(operation.describe(), "Remove field pink from Pony")
+        self.assertEqual(operation.migration_name_fragment, 'remove_pony_pink')
         new_state = project_state.clone()
         operation.state_forwards("test_rmfl", new_state)
         self.assertEqual(len(new_state.models["test_rmfl", "pony"].fields), 2)
@@ -1198,6 +1203,7 @@ class OperationTests(OperationTestBase):
         # Test the state alteration
         operation = migrations.AlterModelTable("Pony", "test_almota_pony_2")
         self.assertEqual(operation.describe(), "Rename table for Pony to test_almota_pony_2")
+        self.assertEqual(operation.migration_name_fragment, 'alter_pony_table')
         new_state = project_state.clone()
         operation.state_forwards("test_almota", new_state)
         self.assertEqual(new_state.models["test_almota", "pony"].options["db_table"], "test_almota_pony_2")
@@ -1286,6 +1292,7 @@ class OperationTests(OperationTestBase):
         # Test the state alteration
         operation = migrations.AlterField("Pony", "pink", models.IntegerField(null=True))
         self.assertEqual(operation.describe(), "Alter field pink on Pony")
+        self.assertEqual(operation.migration_name_fragment, 'alter_pony_pink')
         new_state = project_state.clone()
         operation.state_forwards("test_alfl", new_state)
         self.assertIs(project_state.models['test_alfl', 'pony'].fields['pink'].null, False)
@@ -1543,6 +1550,7 @@ class OperationTests(OperationTestBase):
         # Test the state alteration
         operation = migrations.RenameField("Pony", "pink", "blue")
         self.assertEqual(operation.describe(), "Rename field pink on Pony to blue")
+        self.assertEqual(operation.migration_name_fragment, 'rename_pink_pony_blue')
         new_state = project_state.clone()
         operation.state_forwards("test_rnfl", new_state)
         self.assertIn("blue", new_state.models["test_rnfl", "pony"].fields)
@@ -1624,6 +1632,10 @@ class OperationTests(OperationTestBase):
         # Test the state alteration
         operation = migrations.AlterUniqueTogether("Pony", [("pink", "weight")])
         self.assertEqual(operation.describe(), "Alter unique_together for Pony (1 constraint(s))")
+        self.assertEqual(
+            operation.migration_name_fragment,
+            'alter_pony_unique_together',
+        )
         new_state = project_state.clone()
         operation.state_forwards("test_alunto", new_state)
         self.assertEqual(len(project_state.models["test_alunto", "pony"].options.get("unique_together", set())), 0)
@@ -1675,6 +1687,10 @@ class OperationTests(OperationTestBase):
         index = models.Index(fields=["pink"], name="test_adin_pony_pink_idx")
         operation = migrations.AddIndex("Pony", index)
         self.assertEqual(operation.describe(), "Create index test_adin_pony_pink_idx on field(s) pink of model Pony")
+        self.assertEqual(
+            operation.migration_name_fragment,
+            'pony_test_adin_pony_pink_idx',
+        )
         new_state = project_state.clone()
         operation.state_forwards("test_adin", new_state)
         # Test the database alteration
@@ -1702,6 +1718,10 @@ class OperationTests(OperationTestBase):
         self.assertIndexExists("test_rmin_pony", ["pink", "weight"])
         operation = migrations.RemoveIndex("Pony", "pony_test_idx")
         self.assertEqual(operation.describe(), "Remove index pony_test_idx from Pony")
+        self.assertEqual(
+            operation.migration_name_fragment,
+            'remove_pony_pony_test_idx',
+        )
         new_state = project_state.clone()
         operation.state_forwards("test_rmin", new_state)
         # Test the state alteration
@@ -1789,6 +1809,10 @@ class OperationTests(OperationTestBase):
         # Test the state alteration
         operation = migrations.AlterIndexTogether("Pony", [("pink", "weight")])
         self.assertEqual(operation.describe(), "Alter index_together for Pony (1 constraint(s))")
+        self.assertEqual(
+            operation.migration_name_fragment,
+            'alter_pony_index_together',
+        )
         new_state = project_state.clone()
         operation.state_forwards("test_alinto", new_state)
         self.assertEqual(len(project_state.models["test_alinto", "pony"].options.get("index_together", set())), 0)
@@ -1845,6 +1869,10 @@ class OperationTests(OperationTestBase):
         self.assertEqual(
             gt_operation.describe(), "Create constraint test_add_constraint_pony_pink_gt_2 on model Pony"
         )
+        self.assertEqual(
+            gt_operation.migration_name_fragment,
+            'pony_test_add_constraint_pony_pink_gt_2',
+        )
         # Test the state alteration
         new_state = project_state.clone()
         gt_operation.state_forwards("test_addconstraint", new_state)
@@ -1982,6 +2010,10 @@ class OperationTests(OperationTestBase):
         self.assertEqual(
             gt_operation.describe(), "Remove constraint test_remove_constraint_pony_pink_gt_2 from model Pony"
         )
+        self.assertEqual(
+            gt_operation.migration_name_fragment,
+            'remove_pony_test_remove_constraint_pony_pink_gt_2',
+        )
         # Test state alteration
         new_state = project_state.clone()
         gt_operation.state_forwards("test_removeconstraint", new_state)
@@ -2212,6 +2244,7 @@ class OperationTests(OperationTestBase):
         # Test the state alteration (no DB alteration to test)
         operation = migrations.AlterModelOptions("Pony", {"permissions": [("can_groom", "Can groom")]})
         self.assertEqual(operation.describe(), "Change Meta options on Pony")
+        self.assertEqual(operation.migration_name_fragment, 'alter_pony_options')
         new_state = project_state.clone()
         operation.state_forwards("test_almoop", new_state)
         self.assertEqual(len(project_state.models["test_almoop", "pony"].options.get("permissions", [])), 0)
@@ -2249,6 +2282,10 @@ class OperationTests(OperationTestBase):
         # Test the state alteration
         operation = migrations.AlterOrderWithRespectTo("Rider", "pony")
         self.assertEqual(operation.describe(), "Set order_with_respect_to on Rider to pony")
+        self.assertEqual(
+            operation.migration_name_fragment,
+            'alter_rider_order_with_respect_to',
+        )
         new_state = project_state.clone()
         operation.state_forwards("test_alorwrtto", new_state)
         self.assertIsNone(
@@ -2298,6 +2335,7 @@ class OperationTests(OperationTestBase):
             ]
         )
         self.assertEqual(operation.describe(), "Change managers on Pony")
+        self.assertEqual(operation.migration_name_fragment, 'alter_pony_managers')
         managers = project_state.models["test_almoma", "pony"].managers
         self.assertEqual(managers, [])
 
diff --git a/tests/postgres_tests/test_operations.py b/tests/postgres_tests/test_operations.py
index 8cc9a2b66e..a10f5da440 100644
--- a/tests/postgres_tests/test_operations.py
+++ b/tests/postgres_tests/test_operations.py
@@ -175,6 +175,7 @@ class CreateExtensionTests(PostgreSQLTestCase):
 
     def test_allow_migrate(self):
         operation = CreateExtension('tablefunc')
+        self.assertEqual(operation.migration_name_fragment, 'create_extension_tablefunc')
         project_state = ProjectState()
         new_state = project_state.clone()
         # Create an extension.
@@ -192,6 +193,7 @@ class CreateExtensionTests(PostgreSQLTestCase):
 
     def test_create_existing_extension(self):
         operation = BloomExtension()
+        self.assertEqual(operation.migration_name_fragment, 'create_extension_bloom')
         project_state = ProjectState()
         new_state = project_state.clone()
         # Don't create an existing extension.