[2.0.x] Fixed #28702 -- Made query lookups for CIText fields use citext.

Backport of f0a68c25118786d47041d0a435b2afa953be3c86 from master

3 files changed, 10 insertions, 3 deletions

diff --git a/django/contrib/postgres/fields/citext.py b/django/contrib/postgres/fields/citext.py
index 42660001ae..46f6d3d1c2 100644
--- a/django/contrib/postgres/fields/citext.py
+++ b/django/contrib/postgres/fields/citext.py
@@ -4,6 +4,10 @@ __all__ = ['CICharField', 'CIEmailField', 'CIText', 'CITextField']
 
 
 class CIText:
+
+    def get_internal_type(self):
+        return 'CI' + super().get_internal_type()
+
     def db_type(self, connection):
         return 'citext'
 
diff --git a/django/db/backends/postgresql/operations.py b/django/db/backends/postgresql/operations.py
index 268fa99b51..c4a61f7070 100644
--- a/django/db/backends/postgresql/operations.py
+++ b/django/db/backends/postgresql/operations.py
@@ -77,6 +77,8 @@ class DatabaseOperations(BaseDatabaseOperations):
                            'istartswith', 'endswith', 'iendswith', 'regex', 'iregex'):
             if internal_type in ('IPAddressField', 'GenericIPAddressField'):
                 lookup = "HOST(%s)"
+            elif internal_type in ('CICharField', 'CIEmailField', 'CITextField'):
+                lookup = '%s::citext'
             else:
                 lookup = "%s::text"
 
diff --git a/django/db/backends/postgresql/schema.py b/django/db/backends/postgresql/schema.py
index 20cea3f249..18388cc523 100644
--- a/django/db/backends/postgresql/schema.py
+++ b/django/db/backends/postgresql/schema.py
@@ -107,11 +107,12 @@ class DatabaseSchemaEditor(BaseDatabaseSchemaEditor):
 
     def _alter_field(self, model, old_field, new_field, old_type, new_type,
                      old_db_params, new_db_params, strict=False):
-        # Drop indexes on varchar/text columns that are changing to a different
-        # type.
+        # Drop indexes on varchar/text/citext columns that are changing to a
+        # different type.
         if (old_field.db_index or old_field.unique) and (
             (old_type.startswith('varchar') and not new_type.startswith('varchar')) or
-            (old_type.startswith('text') and not new_type.startswith('text'))
+            (old_type.startswith('text') and not new_type.startswith('text')) or
+            (old_type.startswith('citext') and not new_type.startswith('citext'))
         ):
             index_name = self._create_index_name(model._meta.db_table, [old_field.column], suffix='_like')
             self.execute(self._delete_constraint_sql(self.sql_delete_index, model, index_name))