Add DropIndex operation

Also tests added, changes in states.py

django/db/backends/base/schema.py

@@ -355,6 +355,9 @@ def create_index(self, model, index):
         self.execute(index.as_sql(self, suffix='_idx'))
 
     def drop_index(self, model, index):
+        """
+        Delete an index from model.
+        """
         self.execute(index.remove_sql(self))
 
     def _delete_composed_index(self, model, fields, constraint_kwargs, sql):

django/db/migrations/operations/__init__.py

@@ -1,15 +1,15 @@
 from .fields import AddField, AlterField, RemoveField, RenameField
 from .models import (
-    CreateIndex, AlterIndexTogether, AlterModelManagers, AlterModelOptions,
-    AlterModelTable, AlterOrderWithRespectTo, AlterUniqueTogether, CreateModel,
-    DeleteModel, RenameModel,
+    AlterIndexTogether, AlterModelManagers, AlterModelOptions,
+    AlterModelTable, AlterOrderWithRespectTo, AlterUniqueTogether, CreateIndex,
+    CreateModel, DeleteModel, DropIndex, RenameModel,
 )
 from .special import RunPython, RunSQL, SeparateDatabaseAndState
 
 __all__ = [
     'CreateModel', 'DeleteModel', 'AlterModelTable', 'AlterUniqueTogether',
     'RenameModel', 'AlterIndexTogether', 'AlterModelOptions', 'CreateIndex',
-    'AddField', 'RemoveField', 'AlterField', 'RenameField',
+    'DropIndex', 'AddField', 'RemoveField', 'AlterField', 'RenameField',
     'SeparateDatabaseAndState', 'RunSQL', 'RunPython',
     'AlterOrderWithRespectTo', 'AlterModelManagers',
 ]

django/db/migrations/operations/models.py

@@ -742,8 +742,11 @@ def deconstruct(self):
 
     def state_forwards(self, app_label, state):
         model_state = state.models[app_label, self.model_name.lower()]
-        model_state.options['indexes'] = getattr(model_state.options, 'indexes', []).append(self.index)
-        # model_state.options['indexes'] = getattr(model_state.options, 'indexes', set()).add(self.index)
+        if not hasattr(self.index, 'model'):
+            self.index.model = state.apps.get_model(app_label, self.model_name)
+        if not 'indexes' in model_state.options:
+            model_state.options['indexes'] = []
+        model_state.options['indexes'].append(self.index)
 
     def database_forwards(self, app_label, schema_editor, from_state, to_state):
         to_model = to_state.apps.get_model(app_label, self.model_name)
@@ -768,14 +771,16 @@ def describe(self):
 
 class DropIndex(Operation):
     """
-    Removes an index.
+    Deletes an index of a model.
     """
 
-    def __init__(self, name):
+    def __init__(self, model_name, name):
+        self.model_name = model_name
         self.name = name
 
     def  deconstruct(self):
         kwargs = {
+            'model_name': self.model_name,
             'name': self.name
         }
         return (
@@ -786,28 +791,32 @@ def  deconstruct(self):
 
     def state_forwards(self, app_label, state):
         model_state = state.models[app_label, self.model_name.lower()]
-        # model_state.options['indexes'] = getattr(model_state.options, 'indexes', [])
-
-        if not hasattr(model_state.options, 'indexes'):
-            model_state.options['indexes'] = set()
-        model_state.options['indexes'].add(self.index)
+        i, idx = model_state.get_index_by_name(self.name)
+        idx_list = model_state.options['indexes']
+        model_state.options['indexes'] = idx_list[:i] + idx_list[(i+1):]
+        # del model_state.options['indexes'][i]
+        # model_state.options['indexes'].remove(idx)
 
     def database_forwards(self, app_label, schema_editor, from_state, to_state):
-        model = to_state.apps.get_model(app_label, self.model_name)
-        schema_editor.create_index(
-            model,
-            self.index,
+        to_model = to_state.apps.get_model(app_label, self.model_name)
+        from_model_state = from_state.models[app_label, self.model_name.lower()]
+        _, index = from_model_state.get_index_by_name(self.name)
+        schema_editor.drop_index(
+            to_model,
+            index,
         )
 
     def database_backwards(self, app_label, schema_editor, from_state, to_state):
-        model = to_state.apps.get_model(app_label, self.model_name)
-        schema_editor.drop_index(
-            model,
-            self.index,
+        from_model = from_state.apps.get_model(app_label, self.model_name)
+        to_model_state = to_state.models[app_label, self.model_name.lower()]
+        _, index = to_model_state.get_index_by_name(self.name)
+        schema_editor.create_index(
+            from_model,
+            index,
         )
 
     def describe(self):
-        return "Create index on field(s) %s of model %s" % (
-            ', '.join(self.index.fields),
+        return "Remove index %s from %s" % (
+            self.name,
             self.model_name,
         )

django/db/migrations/state.py

@@ -554,6 +554,13 @@ def get_field_by_name(self, name):
                 return field
         raise ValueError("No field called %s on model %s" % (name, self.name))
 
+    def get_index_by_name(self, name):
+        if 'indexes' in self.options:
+            for i, idx in enumerate(self.options['indexes']):
+                if idx.name == name:
+                    return i, idx
+        raise ValueError("No index named %s on model %s" % (name, self.name))
+
     def __repr__(self):
         return "<ModelState: '%s.%s'>" % (self.app_label, self.name)
 

django/db/models/__init__.py

@@ -11,13 +11,13 @@
 )
 from django.db.models.fields import *  # NOQA
 from django.db.models.fields.files import FileField, ImageField  # NOQA
+from django.db.models.indexes import *
 from django.db.models.fields.proxy import OrderWrt  # NOQA
 from django.db.models.lookups import Lookup, Transform  # NOQA
 from django.db.models.manager import Manager  # NOQA
 from django.db.models.query import (  # NOQA
     Prefetch, Q, QuerySet, prefetch_related_objects,
 )
-from django.db.models.indexes import *
 
 # Imports that would create circular imports if sorted
 from django.db.models.base import DEFERRED, Model  # NOQA isort:skip

django/db/models/indexes.py

@@ -1,3 +1,4 @@
+
 __all__ = ['Index']
 
 class Index(object):

tests/migrations/test_operations.py

@@ -51,7 +51,7 @@ def make_test_state(self, app_label, operation, **kwargs):
         return project_state, new_state
 
     def set_up_test_model(
-            self, app_label, second_model=False, third_model=False,
+            self, app_label, second_model=False, third_model=False, index=False,
             related_model=False, mti_model=False, proxy_model=False, manager_model=False,
             unique_together=False, options=False, db_table=None, index_together=False):
         """
@@ -96,6 +96,11 @@ def set_up_test_model(
             ],
             options=model_options,
         )]
+        if index:
+            operations.append(migrations.CreateIndex(
+                "Pony",
+                models.Index("pink", name="Pony_test_idx")
+            ))
         if second_model:
             operations.append(migrations.CreateModel(
                 "Stable",
@@ -1360,6 +1365,34 @@ def test_create_index(self):
         self.assertEqual(definition[1], [])
         self.assertEqual(definition[2], {'model_name': 'Pony', 'index': index})
 
+    def test_drop_index(self):
+        """
+        Tests the DropIndex operation.
+        """
+        project_state = self.set_up_test_model("test_rmin", index=True)
+        self.assertTableExists("test_rmin_pony")
+        self.assertIndexExists("test_rmin_pony", ["pink"])
+        # Test the state alteration
+        operation = migrations.DropIndex("Pony", "Pony_test_idx")
+        self.assertEqual(operation.describe(), "Remove index Pony_test_idx from Pony")
+        new_state = project_state.clone()
+        operation.state_forwards("test_rmin", new_state)
+        self.assertEqual(len(new_state.models["test_rmin", "pony"].options['indexes']), 0)
+        self.assertIndexExists("test_rmin_pony", ["pink"])
+        # Test the database alteration
+        with connection.schema_editor() as editor:
+            operation.database_forwards("test_rmin", editor, project_state, new_state)
+        self.assertIndexNotExists("test_rmin_pony", ["pink"])
+        # And test reversal
+        with connection.schema_editor() as editor:
+            operation.database_backwards("test_rmin", editor, new_state, project_state)
+        self.assertIndexExists("test_rmin_pony", ["pink"])
+        # And deconstruction
+        definition = operation.deconstruct()
+        self.assertEqual(definition[0], "DropIndex")
+        self.assertEqual(definition[1], [])
+        self.assertEqual(definition[2], {'model_name': "Pony", 'name': 'Pony_test_idx'})
+
     def test_alter_index_together(self):
         """
         Tests the AlterIndexTogether operation.