Support GeneratedField (#335)

* Support GeneratedField

Author: dauinsight

mssql/features.py

@@ -60,6 +60,8 @@ class DatabaseFeatures(BaseDatabaseFeatures):
     supports_default_keyword_in_insert = True
     supports_expression_defaults = True
     supports_default_keyword_in_bulk_insert = True
+    supports_stored_generated_columns = True
+    supports_virtual_generated_columns = True
 
     @cached_property
     def has_zoneinfo_database(self):

mssql/schema.py

@@ -384,6 +384,14 @@ def _delete_deferred_unique_indexes_for_field(self, field):
     def _add_deferred_unique_index_for_field(self, field, statement):
         self._deferred_unique_indexes[str(field)].append(statement)
 
+    def _column_generated_sql(self, field):
+        """Return the SQL to use in a GENERATED ALWAYS clause."""
+        expression_sql, params = field.generated_sql(self.connection)
+        persistency_sql = "PERSISTED" if field.db_persist else ""
+        if params:
+            expression_sql = expression_sql % tuple(self.quote_value(p) for p in params)
+        return f"AS {expression_sql} {persistency_sql}"
+
     def _alter_field(self, model, old_field, new_field, old_type, new_type,
                      old_db_params, new_db_params, strict=False):
         """Actually perform a "physical" (non-ManyToMany) field update."""
@@ -1016,6 +1024,9 @@ def add_field(self, model, field):
         # It might not actually have a column behind it
         if definition is None:
             return
+        # Remove column type from definition if field is generated
+        if (django_version >= (5,0) and field.generated):
+            definition = definition[definition.find('AS'):]
         # Nullable columns with default values require 'WITH VALUES' to set existing rows
         if 'DEFAULT' in definition and field.null:
             definition = definition.replace('NULL', 'WITH VALUES')
@@ -1218,6 +1229,9 @@ def create_model(self, model):
             definition, extra_params = self.column_sql(model, field)
             if definition is None:
                 continue
+            # Remove column type from definition if field is generated
+            if (django_version >= (5,0) and field.generated):
+                definition = definition[definition.find('AS'):]
 
             if (self.connection.features.supports_nullable_unique_constraints and
                     not field.many_to_many and field.null and field.unique):