Fixed #27859 -- Ignored db_index for TextField/BinaryField on Oracle and MySQL.

Thanks Zubair Alam for the initial patch and Tim Graham for the review.

tests/schema/models.py

@@ -17,6 +17,13 @@ class Author(models.Model):
         apps = new_apps
 
 
+class AuthorTextFieldWithIndex(models.Model):
+    text_field = models.TextField(db_index=True)
+
+    class Meta:
+        apps = new_apps
+
+
 class AuthorWithDefaultHeight(models.Model):
     name = models.CharField(max_length=255)
     height = models.PositiveIntegerField(null=True, blank=True, default=42)

tests/schema/tests.py

@@ -29,11 +29,11 @@ from .fields import (
     CustomManyToManyField, InheritedManyToManyField, MediumBlobField,
 )
 from .models import (
-    Author, AuthorWithDefaultHeight, AuthorWithEvenLongerName,
-    AuthorWithIndexedName, Book, BookForeignObj, BookWeak, BookWithLongName,
-    BookWithO2O, BookWithoutAuthor, BookWithSlug, IntegerPK, Node, Note,
-    NoteRename, Tag, TagIndexed, TagM2MTest, TagUniqueRename, Thing,
-    UniqueTest, new_apps,
+    Author, AuthorTextFieldWithIndex, AuthorWithDefaultHeight,
+    AuthorWithEvenLongerName, AuthorWithIndexedName, Book, BookForeignObj,
+    BookWeak, BookWithLongName, BookWithO2O, BookWithoutAuthor, BookWithSlug,
+    IntegerPK, Node, Note, NoteRename, Tag, TagIndexed, TagM2MTest,
+    TagUniqueRename, Thing, UniqueTest, new_apps,
 )
 
 
@@ -1749,6 +1749,13 @@ class SchemaTests(TransactionTestCase):
             self.get_indexes(Book._meta.db_table),
         )
 
+    def test_text_field_with_db_index(self):
+        with connection.schema_editor() as editor:
+            editor.create_model(AuthorTextFieldWithIndex)
+        # The text_field index is present if the database supports it.
+        assertion = self.assertIn if connection.features.supports_index_on_text_field else self.assertNotIn
+        assertion('text_field', self.get_indexes(AuthorTextFieldWithIndex._meta.db_table))
+
     def test_primary_key(self):
         """
         Tests altering of the primary key