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.

7 files changed, 225 insertions, 12 deletions

diff --git a/django/db/backends/base/schema.py b/django/db/backends/base/schema.py
index 156f119c0d..b6510ca626 100644
--- a/django/db/backends/base/schema.py
+++ b/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 % {
diff --git a/django/db/migrations/operations/__init__.py b/django/db/migrations/operations/__init__.py
index 472b482eff..894f2ab9c5 100644
--- a/django/db/migrations/operations/__init__.py
+++ b/django/db/migrations/operations/__init__.py
@@ -1,15 +1,15 @@
 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',
 ]
diff --git a/django/db/migrations/operations/models.py b/django/db/migrations/operations/models.py
index b7d4046f87..4c9467cc0d 100644
--- a/django/db/migrations/operations/models.py
+++ b/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)
diff --git a/django/db/migrations/state.py b/django/db/migrations/state.py
index 44eab227ed..74f7475cf8 100644
--- a/django/db/migrations/state.py
+++ b/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)
 
diff --git a/django/db/models/__init__.py b/django/db/models/__init__.py
index 958b122d9f..2ce935d3f8 100644
--- a/django/db/models/__init__.py
+++ b/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
diff --git a/django/db/models/indexes.py b/django/db/models/indexes.py
new file mode 100644
index 0000000000..15d618156e
--- /dev/null
+++ b/django/db/models/indexes.py
@@ -0,0 +1,113 @@
+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)
diff --git a/django/db/models/options.py b/django/db/models/options.py
index ef13c496f8..19dce58663 100644
--- a/django/db/models/options.py
+++ b/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',
 )