Fixed #26709 -- Added class-based indexes.

Added the AddIndex and RemoveIndex operations to use them in migrations.

Thanks markush, mjtamlyn, timgraham, and charettes for review and advice.

django/db/backends/base/schema.py

@@ -316,6 +316,18 @@ class BaseDatabaseSchemaEditor(object):
             "table": self.quote_name(model._meta.db_table),
         })
 
+    def add_index(self, index):
+        """
+        Add an index on a model.
+        """
+        self.execute(index.create_sql(self))
+
+    def remove_index(self, index):
+        """
+        Remove an index from a model.
+        """
+        self.execute(index.remove_sql(self))
+
     def alter_unique_together(self, model, old_unique_together, new_unique_together):
         """
         Deals with a model changing its unique_together.
@@ -836,12 +848,7 @@ class BaseDatabaseSchemaEditor(object):
             index_name = "D%s" % index_name[:-1]
         return index_name
 
-    def _create_index_sql(self, model, fields, suffix="", sql=None):
-        """
-        Return the SQL statement to create the index for one or several fields.
-        `sql` can be specified if the syntax differs from the standard (GIS
-        indexes, ...).
-        """
+    def _get_index_tablespace_sql(self, model, fields):
         if len(fields) == 1 and fields[0].db_tablespace:
             tablespace_sql = self.connection.ops.tablespace_sql(fields[0].db_tablespace)
         elif model._meta.db_tablespace:
@@ -850,7 +857,15 @@ class BaseDatabaseSchemaEditor(object):
             tablespace_sql = ""
         if tablespace_sql:
             tablespace_sql = " " + tablespace_sql
+        return tablespace_sql
 
+    def _create_index_sql(self, model, fields, suffix="", sql=None):
+        """
+        Return the SQL statement to create the index for one or several fields.
+        `sql` can be specified if the syntax differs from the standard (GIS
+        indexes, ...).
+        """
+        tablespace_sql = self._get_index_tablespace_sql(model, fields)
         columns = [field.column for field in fields]
         sql_create_index = sql or self.sql_create_index
         return sql_create_index % {

django/db/migrations/operations/__init__.py

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

django/db/migrations/operations/models.py

@@ -742,3 +742,80 @@ class AlterModelManagers(ModelOptionOperation):
 
     def describe(self):
         return "Change managers on %s" % (self.name, )
+
+
+class AddIndex(Operation):
+    """
+    Add an index on a model.
+    """
+
+    def __init__(self, model_name, index):
+        self.model_name = model_name
+        self.index = index
+
+    def state_forwards(self, app_label, state):
+        model_state = state.models[app_label, self.model_name.lower()]
+        self.index.model = state.apps.get_model(app_label, self.model_name)
+        model_state.options['indexes'].append(self.index)
+
+    def database_forwards(self, app_label, schema_editor, from_state, to_state):
+        schema_editor.add_index(self.index)
+
+    def database_backwards(self, app_label, schema_editor, from_state, to_state):
+        schema_editor.remove_index(self.index)
+
+    def deconstruct(self):
+        kwargs = {
+            'model_name': self.model_name,
+            'index': self.index,
+        }
+        return (
+            self.__class__.__name__,
+            [],
+            kwargs,
+        )
+
+    def describe(self):
+        return 'Create index on field(s) %s of model %s' % (
+            ', '.join(self.index.fields),
+            self.model_name,
+        )
+
+
+class RemoveIndex(Operation):
+    """
+    Remove an index from a model.
+    """
+
+    def __init__(self, model_name, name):
+        self.model_name = model_name
+        self.name = name
+
+    def state_forwards(self, app_label, state):
+        model_state = state.models[app_label, self.model_name.lower()]
+        indexes = model_state.options['indexes']
+        model_state.options['indexes'] = [idx for idx in indexes if idx.name != self.name]
+
+    def database_forwards(self, app_label, schema_editor, from_state, to_state):
+        from_model_state = from_state.models[app_label, self.model_name.lower()]
+        index = from_model_state.get_index_by_name(self.name)
+        schema_editor.remove_index(index)
+
+    def database_backwards(self, app_label, schema_editor, from_state, to_state):
+        to_model_state = to_state.models[app_label, self.model_name.lower()]
+        index = to_model_state.get_index_by_name(self.name)
+        schema_editor.add_index(index)
+
+    def deconstruct(self):
+        kwargs = {
+            'model_name': self.model_name,
+            'name': self.name,
+        }
+        return (
+            self.__class__.__name__,
+            [],
+            kwargs,
+        )
+
+    def describe(self):
+        return 'Remove index %s from %s' % (self.name, self.model_name)

django/db/migrations/state.py

@@ -330,6 +330,7 @@ class ModelState(object):
         self.name = force_text(name)
         self.fields = fields
         self.options = options or {}
+        self.options.setdefault('indexes', [])
         self.bases = bases or (models.Model, )
         self.managers = managers or []
         # Sanity-check that fields is NOT a dict. It must be ordered.
@@ -557,6 +558,12 @@ class ModelState(object):
                 return field
         raise ValueError("No field called %s on model %s" % (name, self.name))
 
+    def get_index_by_name(self, name):
+        for index in self.options['indexes']:
+            if index.name == name:
+                return index
+        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

@@ -12,6 +12,7 @@ from django.db.models.expressions import (  # NOQA
 from django.db.models.fields import *  # NOQA
 from django.db.models.fields.files import FileField, ImageField  # NOQA
 from django.db.models.fields.proxy import OrderWrt  # NOQA
+from django.db.models.indexes import *  # 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

django/db/models/indexes.py

+from __future__ import unicode_literals
+
+import hashlib
+
+from django.utils.encoding import force_bytes
+from django.utils.functional import cached_property
+
+__all__ = ['Index']
+
+# The max length of the names of the indexes (restricted to 30 due to Oracle)
+MAX_NAME_LENGTH = 30
+
+
+class Index(object):
+    suffix = 'idx'
+
+    def __init__(self, fields=[], name=None):
+        if not fields:
+            raise ValueError('At least one field is required to define an index.')
+        self.fields = fields
+        self._name = name or ''
+        if self._name:
+            errors = self.check_name()
+            if len(self._name) > MAX_NAME_LENGTH:
+                errors.append('Index names cannot be longer than %s characters.' % MAX_NAME_LENGTH)
+            if errors:
+                raise ValueError(errors)
+
+    @cached_property
+    def name(self):
+        if not self._name:
+            self._name = self.get_name()
+            self.check_name()
+        return self._name
+
+    def check_name(self):
+        errors = []
+        # Name can't start with an underscore on Oracle; prepend D if needed.
+        if self._name[0] == '_':
+            errors.append('Index names cannot start with an underscore (_).')
+            self._name = 'D%s' % self._name[1:]
+        # Name can't start with a number on Oracle; prepend D if needed.
+        elif self._name[0].isdigit():
+            errors.append('Index names cannot start with a number (0-9).')
+            self._name = 'D%s' % self._name[1:]
+        return errors
+
+    def create_sql(self, schema_editor):
+        fields = [self.model._meta.get_field(field) for field in self.fields]
+        tablespace_sql = schema_editor._get_index_tablespace_sql(self.model, fields)
+        columns = [field.column for field in fields]
+
+        quote_name = schema_editor.quote_name
+        return schema_editor.sql_create_index % {
+            'table': quote_name(self.model._meta.db_table),
+            'name': quote_name(self.name),
+            'columns': ', '.join(quote_name(column) for column in columns),
+            'extra': tablespace_sql,
+        }
+
+    def remove_sql(self, schema_editor):
+        quote_name = schema_editor.quote_name
+        return schema_editor.sql_delete_index % {
+            'table': quote_name(self.model._meta.db_table),
+            'name': quote_name(self.name),
+        }
+
+    def deconstruct(self):
+        path = '%s.%s' % (self.__class__.__module__, self.__class__.__name__)
+        path = path.replace('django.db.models.indexes', 'django.db.models')
+        return (path, (), {'fields': self.fields})
+
+    @staticmethod
+    def _hash_generator(*args):
+        """
+        Generate a 32-bit digest of a set of arguments that can be used to
+        shorten identifying names.
+        """
+        h = hashlib.md5()
+        for arg in args:
+            h.update(force_bytes(arg))
+        return h.hexdigest()[:6]
+
+    def get_name(self):
+        """
+        Generate a unique name for the index.
+
+        The name is divided into 3 parts - table name (12 chars), field name
+        (8 chars) and unique hash + suffix (10 chars). Each part is made to
+        fit its size by truncating the excess length.
+        """
+        table_name = self.model._meta.db_table
+        column_names = [self.model._meta.get_field(field).column for field in self.fields]
+        hash_data = [table_name] + column_names + [self.suffix]
+        index_name = '%s_%s_%s' % (
+            table_name[:11],
+            column_names[0][:7],
+            '%s_%s' % (self._hash_generator(*hash_data), self.suffix),
+        )
+        assert len(index_name) <= 30, (
+            'Index too long for multiple database support. Is self.suffix '
+            'longer than 3 characters?'
+        )
+        return index_name
+
+    def __repr__(self):
+        return "<%s: fields='%s'>" % (self.__class__.__name__, ', '.join(self.fields))
+
+    def __eq__(self, other):
+        return (self.__class__ == other.__class__) and (self.deconstruct() == other.deconstruct())
+
+    def __ne__(self, other):
+        return not (self == other)

django/db/models/options.py

@@ -43,7 +43,7 @@ DEFAULT_NAMES = (
     'auto_created', 'index_together', 'apps', 'default_permissions',
     'select_on_save', 'default_related_name', 'required_db_features',
     'required_db_vendor', 'base_manager_name', 'default_manager_name',
-    'manager_inheritance_from_future',
+    'manager_inheritance_from_future', 'indexes',
 )
 
 

docs/index.txt

@@ -82,6 +82,7 @@ manipulating the data of your Web application. Learn more about it below:
 * **Models:**
   :doc:`Introduction to models <topics/db/models>` |
   :doc:`Field types <ref/models/fields>` |
+  :doc:`Indexes <ref/models/indexes>` |
   :doc:`Meta options <ref/models/options>` |
   :doc:`Model class <ref/models/class>`
 

docs/ref/migration-operations.txt

@@ -192,6 +192,43 @@ field like ``models.IntegerField()`` on most databases.
 Changes a field's name (and, unless :attr:`~django.db.models.Field.db_column`
 is set, its column name).
 
+``AddIndex``
+------------
+
+.. class:: AddIndex(model_name, index)
+
+.. versionadded:: 1.11
+
+Creates an index in the database table for the model with ``model_name``.
+``index`` is an instance of the :class:`~django.db.models.Index` class.
+
+For example, to add an index on the ``title`` and ``author`` fields of the
+``Book`` model::
+
+    from django.db import migrations, models
+
+    class Migration(migrations.Migration):
+        operations = [
+            migrations.AddIndex(
+                'Book',
+                models.Index(fields=['title', 'author'], name='my_index_name'),
+            ),
+        ]
+
+If you're writing your own migration to add an index, it's recommended to pass
+a ``name`` to the ``index`` as done above so that you can reference it if you
+later want to remove it. Otherwise, a name will be autogenerated and you'll
+have to inspect the database to find the index name if you want to remove it.
+
+``RemoveIndex``
+---------------
+
+.. class:: RemoveIndex(model_name, name)
+
+.. versionadded:: 1.11
+
+Removes the index named ``name`` from the model with ``model_name``.
+
 Special Operations
 ==================
 

docs/ref/models/index.txt

@@ -8,6 +8,7 @@ Model API reference. For introductory material, see :doc:`/topics/db/models`.
    :maxdepth: 1
 
    fields
+   indexes
    meta
    relations
    class

docs/ref/models/indexes.txt

+=====================
+Model index reference
+=====================
+
+.. module:: django.db.models.indexes
+
+.. currentmodule:: django.db.models
+
+.. versionadded:: 1.11
+
+Index classes ease creating database indexes. This document explains the API
+references of :class:`Index` which includes the `index options`_.
+
+.. admonition:: Referencing built-in indexes
+
+    Indexes are defined in ``django.db.models.indexes``, but for convenience
+    they're imported into :mod:`django.db.models`. The standard convention is
+    to use ``from django.db import models`` and refer to the indexes as
+    ``models.<IndexClass>``.
+
+``Index`` options
+=================
+
+.. class:: Index(fields=[], name=None)
+
+    Creates an index (B-Tree) in the database.
+
+``fields``
+-----------
+
+.. attribute:: Index.fields
+
+A list of the name of the fields on which the index is desired.
+
+``name``
+--------
+
+.. attribute:: Index.name
+
+The name of the index. If ``name`` isn't provided Django will auto-generate a
+name. For compatibility with different databases, index names cannot be longer
+than 30 characters and shouldn't start with a number (0-9) or underscore (_).
+
+.. seealso::
+
+    Use the :class:`~django.db.migrations.operations.AddIndex` and
+    :class:`~django.db.migrations.operations.RemoveIndex` operations to add
+    and remove indexes.

tests/migrations/test_autodetector.py

@@ -1263,7 +1263,9 @@ class AutodetectorTests(TestCase):
         # Right number/type of migrations?
         self.assertNumberMigrations(changes, "testapp", 1)
         self.assertOperationTypes(changes, "testapp", 0, ["CreateModel"])
-        self.assertOperationAttributes(changes, "testapp", 0, 0, name="AuthorProxy", options={"proxy": True})
+        self.assertOperationAttributes(
+            changes, "testapp", 0, 0, name="AuthorProxy", options={"proxy": True, "indexes": []}
+        )
         # Now, we test turning a proxy model into a non-proxy model
         # It should delete the proxy then make the real one
         changes = self.get_changes(
@@ -1273,7 +1275,7 @@ class AutodetectorTests(TestCase):
         self.assertNumberMigrations(changes, "testapp", 1)
         self.assertOperationTypes(changes, "testapp", 0, ["DeleteModel", "CreateModel"])
         self.assertOperationAttributes(changes, "testapp", 0, 0, name="AuthorProxy")
-        self.assertOperationAttributes(changes, "testapp", 0, 1, name="AuthorProxy", options={})
+        self.assertOperationAttributes(changes, "testapp", 0, 1, name="AuthorProxy", options={"indexes": []})
 
     def test_proxy_custom_pk(self):
         """
@@ -1296,7 +1298,9 @@ class AutodetectorTests(TestCase):
         # Right number/type of migrations?
         self.assertNumberMigrations(changes, 'testapp', 1)
         self.assertOperationTypes(changes, 'testapp', 0, ["CreateModel"])
-        self.assertOperationAttributes(changes, 'testapp', 0, 0, name="AuthorUnmanaged", options={"managed": False})
+        self.assertOperationAttributes(
+            changes, 'testapp', 0, 0, name="AuthorUnmanaged", options={"managed": False, "indexes": []}
+        )
 
     def test_unmanaged_to_managed(self):
         # Now, we test turning an unmanaged model into a managed model

tests/migrations/test_operations.py

@@ -51,7 +51,7 @@ class OperationTestBase(MigrationTestBase):
         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, multicol_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 @@ class OperationTestBase(MigrationTestBase):
             ],
             options=model_options,
         )]
+        if multicol_index:
+            operations.append(migrations.AddIndex(
+                "Pony",
+                models.Index(fields=["pink", "weight"], name="pony_test_idx")
+            ))
         if second_model:
             operations.append(migrations.CreateModel(
                 "Stable",
@@ -1375,6 +1380,60 @@ class OperationTests(OperationTestBase):
         operation = migrations.AlterUniqueTogether("Pony", None)
         self.assertEqual(operation.describe(), "Alter unique_together for Pony (0 constraint(s))")
 
+    def test_add_index(self):
+        """
+        Test the AddIndex operation.
+        """
+        project_state = self.set_up_test_model("test_adin")
+        index = models.Index(fields=["pink"])
+        operation = migrations.AddIndex("Pony", index)
+        self.assertEqual(operation.describe(), "Create index on field(s) pink of model Pony")
+        new_state = project_state.clone()
+        operation.state_forwards("test_adin", new_state)
+        # Test the database alteration
+        self.assertEqual(len(new_state.models["test_adin", "pony"].options['indexes']), 1)
+        self.assertIndexNotExists("test_adin_pony", ["pink"])
+        with connection.schema_editor() as editor:
+            operation.database_forwards("test_adin", editor, project_state, new_state)
+        self.assertIndexExists("test_adin_pony", ["pink"])
+        # And test reversal
+        with connection.schema_editor() as editor:
+            operation.database_backwards("test_adin", editor, new_state, project_state)
+        self.assertIndexNotExists("test_adin_pony", ["pink"])
+        # And deconstruction
+        definition = operation.deconstruct()
+        self.assertEqual(definition[0], "AddIndex")
+        self.assertEqual(definition[1], [])
+        self.assertEqual(definition[2], {'model_name': "Pony", 'index': index})
+
+    def test_remove_index(self):
+        """
+        Test the RemoveIndex operation.
+        """
+        project_state = self.set_up_test_model("test_rmin", multicol_index=True)
+        self.assertTableExists("test_rmin_pony")
+        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")
+        new_state = project_state.clone()
+        operation.state_forwards("test_rmin", new_state)
+        # Test the state alteration
+        self.assertEqual(len(new_state.models["test_rmin", "pony"].options['indexes']), 0)
+        self.assertIndexExists("test_rmin_pony", ["pink", "weight"])
+        # 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", "weight"])
+        # 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", "weight"])
+        # And deconstruction
+        definition = operation.deconstruct()
+        self.assertEqual(definition[0], "RemoveIndex")
+        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.

tests/migrations/test_state.py

@@ -125,7 +125,7 @@ class StateTests(SimpleTestCase):
         self.assertIs(author_state.fields[3][1].null, True)
         self.assertEqual(
             author_state.options,
-            {"unique_together": {("name", "bio")}, "index_together": {("bio", "age")}}
+            {"unique_together": {("name", "bio")}, "index_together": {("bio", "age")}, "indexes": []}
         )
         self.assertEqual(author_state.bases, (models.Model, ))
 
@@ -135,13 +135,13 @@ class StateTests(SimpleTestCase):
         self.assertEqual(book_state.fields[1][1].max_length, 1000)
         self.assertIs(book_state.fields[2][1].null, False)
         self.assertEqual(book_state.fields[3][1].__class__.__name__, "ManyToManyField")
-        self.assertEqual(book_state.options, {"verbose_name": "tome", "db_table": "test_tome"})
+        self.assertEqual(book_state.options, {"verbose_name": "tome", "db_table": "test_tome", "indexes": []})
         self.assertEqual(book_state.bases, (models.Model, ))
 
         self.assertEqual(author_proxy_state.app_label, "migrations")
         self.assertEqual(author_proxy_state.name, "AuthorProxy")
         self.assertEqual(author_proxy_state.fields, [])
-        self.assertEqual(author_proxy_state.options, {"proxy": True, "ordering": ["name"]})
+        self.assertEqual(author_proxy_state.options, {"proxy": True, "ordering": ["name"], "indexes": []})
         self.assertEqual(author_proxy_state.bases, ("migrations.author", ))
 
         self.assertEqual(sub_author_state.app_label, "migrations")
@@ -960,7 +960,7 @@ class ModelStateTests(SimpleTestCase):
         self.assertEqual(author_state.fields[1][1].max_length, 255)
         self.assertIs(author_state.fields[2][1].null, False)
         self.assertIs(author_state.fields[3][1].null, True)
-        self.assertEqual(author_state.options, {'swappable': 'TEST_SWAPPABLE_MODEL'})
+        self.assertEqual(author_state.options, {'swappable': 'TEST_SWAPPABLE_MODEL', 'indexes': []})
         self.assertEqual(author_state.bases, (models.Model, ))
         self.assertEqual(author_state.managers, [])
 

tests/model_indexes/models.py

+from django.db import models
+
+
+class Book(models.Model):
+    title = models.CharField(max_length=50)
+    author = models.CharField(max_length=50)
+    pages = models.IntegerField(db_column='page_count')

tests/model_indexes/tests.py

+from django.db import models
+from django.test import TestCase
+
+from .models import Book
+
+
+class IndexesTests(TestCase):
+
+    def test_repr(self):
+        index = models.Index(fields=['title'])
+        multi_col_index = models.Index(fields=['title', 'author'])
+        self.assertEqual(repr(index), "<Index: fields='title'>")
+        self.assertEqual(repr(multi_col_index), "<Index: fields='title, author'>")
+
+    def test_eq(self):
+        index = models.Index(fields=['title'])
+        same_index = models.Index(fields=['title'])
+        another_index = models.Index(fields=['title', 'author'])
+        self.assertEqual(index, same_index)
+        self.assertNotEqual(index, another_index)
+
+    def test_raises_error_without_field(self):
+        msg = 'At least one field is required to define an index.'
+        with self.assertRaisesMessage(ValueError, msg):
+            models.Index()
+
+    def test_max_name_length(self):
+        msg = 'Index names cannot be longer than 30 characters.'
+        with self.assertRaisesMessage(ValueError, msg):
+            models.Index(fields=['title'], name='looooooooooooong_index_name_idx')
+
+    def test_name_constraints(self):
+        msg = 'Index names cannot start with an underscore (_).'
+        with self.assertRaisesMessage(ValueError, msg):
+            models.Index(fields=['title'], name='_name_starting_with_underscore')
+
+        msg = 'Index names cannot start with a number (0-9).'
+        with self.assertRaisesMessage(ValueError, msg):
+            models.Index(fields=['title'], name='5name_starting_with_number')
+
+    def test_name_auto_generation(self):
+        index = models.Index(fields=['author'])
+        index.model = Book
+        self.assertEqual(index.name, 'model_index_author_0f5565_idx')
+
+        # fields may be truncated in the name. db_column is used for naming.
+        long_field_index = models.Index(fields=['pages'])
+        long_field_index.model = Book
+        self.assertEqual(long_field_index.name, 'model_index_page_co_69235a_idx')
+
+        # suffix can't be longer than 3 characters.
+        long_field_index.suffix = 'suff'
+        msg = 'Index too long for multiple database support. Is self.suffix longer than 3 characters?'
+        with self.assertRaisesMessage(AssertionError, msg):
+            long_field_index.get_name()
+
+    def test_deconstruction(self):
+        index = models.Index(fields=['title'])
+        path, args, kwargs = index.deconstruct()
+        self.assertEqual(path, 'django.db.models.Index')
+        self.assertEqual(args, ())
+        self.assertEqual(kwargs, {'fields': ['title']})

tests/schema/tests.py

@@ -16,6 +16,7 @@ from django.db.models.fields import (
 from django.db.models.fields.related import (
     ForeignKey, ForeignObject, ManyToManyField, OneToOneField,
 )
+from django.db.models.indexes import Index
 from django.db.transaction import atomic
 from django.test import (
     TransactionTestCase, mock, skipIfDBFeature, skipUnlessDBFeature,
@@ -1443,6 +1444,26 @@ class SchemaTests(TransactionTestCase):
         columns = self.column_classes(Author)
         self.assertEqual(columns['name'][0], "CharField")
 
+    def test_add_remove_index(self):
+        """
+        Tests index addition and removal
+        """
+        # Create the table
+        with connection.schema_editor() as editor:
+            editor.create_model(Author)
+        # Ensure the table is there and has no index
+        self.assertNotIn('title', self.get_indexes(Author._meta.db_table))
+        # Add the index
+        index = Index(fields=['name'], name='author_title_idx')
+        index.model = Author
+        with connection.schema_editor() as editor:
+            editor.add_index(index)
+        self.assertIn('name', self.get_indexes(Author._meta.db_table))
+        # Drop the index
+        with connection.schema_editor() as editor:
+            editor.remove_index(index)
+        self.assertNotIn('name', self.get_indexes(Author._meta.db_table))
+
     def test_indexes(self):
         """
         Tests creation/altering of indexes