Fixed #34219 -- Preserved Char/TextField.db_collation when altering column type.

This moves setting a database collation to the column type alteration
as both must be set at the same time.

This should also avoid another layer of the column type alteration when
adding database comments support (#18468).

1 files changed, 12 insertions, 5 deletions

diff --git a/django/db/backends/postgresql/schema.py b/django/db/backends/postgresql/schema.py
index 1bd72bc0cb..2887071254 100644
--- a/django/db/backends/postgresql/schema.py
+++ b/django/db/backends/postgresql/schema.py
@@ -140,7 +140,9 @@ class DatabaseSchemaEditor(BaseDatabaseSchemaEditor):
                     return sequence["name"]
         return None
 
-    def _alter_column_type_sql(self, model, old_field, new_field, new_type):
+    def _alter_column_type_sql(
+        self, model, old_field, new_field, new_type, old_collation, new_collation
+    ):
         # Drop indexes on varchar/text/citext columns that are changing to a
         # different type.
         old_db_params = old_field.db_parameters(connection=self.connection)
@@ -155,7 +157,9 @@ class DatabaseSchemaEditor(BaseDatabaseSchemaEditor):
             )
             self.execute(self._delete_index_sql(model, index_name))
 
-        self.sql_alter_column_type = "ALTER COLUMN %(column)s TYPE %(type)s"
+        self.sql_alter_column_type = (
+            "ALTER COLUMN %(column)s TYPE %(type)s%(collation)s"
+        )
         # Cast when data type changed.
         if using_sql := self._using_sql(new_field, old_field):
             self.sql_alter_column_type += using_sql
@@ -178,6 +182,7 @@ class DatabaseSchemaEditor(BaseDatabaseSchemaEditor):
                     % {
                         "column": self.quote_name(column),
                         "type": new_type,
+                        "collation": "",
                     },
                     [],
                 ),
@@ -204,7 +209,7 @@ class DatabaseSchemaEditor(BaseDatabaseSchemaEditor):
             )
             column = strip_quotes(new_field.column)
             fragment, _ = super()._alter_column_type_sql(
-                model, old_field, new_field, new_type
+                model, old_field, new_field, new_type, old_collation, new_collation
             )
             # Drop the sequence if exists (Django 4.1+ identity columns don't
             # have it).
@@ -222,7 +227,7 @@ class DatabaseSchemaEditor(BaseDatabaseSchemaEditor):
             return fragment, other_actions
         elif new_is_auto and old_is_auto and old_internal_type != new_internal_type:
             fragment, _ = super()._alter_column_type_sql(
-                model, old_field, new_field, new_type
+                model, old_field, new_field, new_type, old_collation, new_collation
             )
             column = strip_quotes(new_field.column)
             db_types = {
@@ -246,7 +251,9 @@ class DatabaseSchemaEditor(BaseDatabaseSchemaEditor):
                 ]
             return fragment, other_actions
         else:
-            return super()._alter_column_type_sql(model, old_field, new_field, new_type)
+            return super()._alter_column_type_sql(
+                model, old_field, new_field, new_type, old_collation, new_collation
+            )
 
     def _alter_column_collation_sql(
         self, model, new_field, new_type, new_collation, old_field