[1.8.x] Fixed #25412 -- Fixed missing PostgreSQL index on Char/TextField when using AlterField.

Thanks to Emanuele Palazzetti for the help.

Backport of 3a36c8079544c83dcdea4e52181efcd2d1e86b9c from master

1 files changed, 45 insertions, 17 deletions

diff --git a/django/db/backends/postgresql_psycopg2/schema.py b/django/db/backends/postgresql_psycopg2/schema.py
index 9446bfde43..e425154815 100644
--- a/django/db/backends/postgresql_psycopg2/schema.py
+++ b/django/db/backends/postgresql_psycopg2/schema.py
@@ -20,25 +20,33 @@ class DatabaseSchemaEditor(BaseDatabaseSchemaEditor):
             return output
 
         for field in model._meta.local_fields:
-            db_type = field.db_type(connection=self.connection)
-            if db_type is not None and (field.db_index or field.unique):
-                # Fields with database column types of `varchar` and `text` need
-                # a second index that specifies their operator class, which is
-                # needed when performing correct LIKE queries outside the
-                # C locale. See #12234.
-                #
-                # The same doesn't apply to array fields such as varchar[size]
-                # and text[size], so skip them.
-                if '[' in db_type:
-                    continue
-                if db_type.startswith('varchar'):
-                    output.append(self._create_index_sql(
-                        model, [field], suffix='_like', sql=self.sql_create_varchar_index))
-                elif db_type.startswith('text'):
-                    output.append(self._create_index_sql(
-                        model, [field], suffix='_like', sql=self.sql_create_text_index))
+            like_index_statement = self._create_like_index_sql(model, field)
+            if like_index_statement is not None:
+                output.append(like_index_statement)
         return output
 
+    def _create_like_index_sql(self, model, field):
+        """
+        Return the statement to create an index with varchar operator pattern
+        when the column type is 'varchar' or 'text', otherwise return None.
+        """
+        db_type = field.db_type(connection=self.connection)
+        if db_type is not None and (field.db_index or field.unique):
+            # Fields with database column types of `varchar` and `text` need
+            # a second index that specifies their operator class, which is
+            # needed when performing correct LIKE queries outside the
+            # C locale. See #12234.
+            #
+            # The same doesn't apply to array fields such as varchar[size]
+            # and text[size], so skip them.
+            if '[' in db_type:
+                return None
+            if db_type.startswith('varchar'):
+                return self._create_index_sql(model, [field], suffix='_like', sql=self.sql_create_varchar_index)
+            elif db_type.startswith('text'):
+                return self._create_index_sql(model, [field], suffix='_like', sql=self.sql_create_text_index)
+        return None
+
     def _alter_column_type_sql(self, table, old_field, new_field, new_type):
         """
         Makes ALTER TYPE with SERIAL make sense.
@@ -91,3 +99,23 @@ class DatabaseSchemaEditor(BaseDatabaseSchemaEditor):
             return super(DatabaseSchemaEditor, self)._alter_column_type_sql(
                 table, old_field, new_field, new_type
             )
+
+    def _alter_field(self, model, old_field, new_field, old_type, new_type,
+                     old_db_params, new_db_params, strict=False):
+        super(DatabaseSchemaEditor, self)._alter_field(
+            model, old_field, new_field, old_type, new_type, old_db_params,
+            new_db_params, strict,
+        )
+        # Added an index? Create any PostgreSQL-specific indexes.
+        if ((not old_field.db_index and new_field.db_index) or (not old_field.unique and new_field.unique)):
+            like_index_statement = self._create_like_index_sql(model, new_field)
+            if like_index_statement is not None:
+                self.execute(like_index_statement)
+
+        # Removed an index? Drop any PostgreSQL-specific indexes.
+        if ((not new_field.db_index and old_field.db_index) or (not new_field.unique and old_field.unique)):
+            index_to_remove = self._create_index_name(model, [old_field.column], suffix='_like')
+            index_names = self._constraint_names(model, [old_field.column], index=True)
+            for index_name in index_names:
+                if index_name == index_to_remove:
+                    self.execute(self._delete_constraint_sql(self.sql_delete_index, model, index_name))