Fix dataclass field type in _row_to_sql (#266)

In complement to #257 , dataclass field type needs to be adjusted in
other places.
This fix is required by databrickslabs/ucx#2526

Co-authored-by: Eric Vergnaud <eric.vergnaud@databricks.com>

src/databricks/labs/lsql/backends.py

@@ -69,14 +69,7 @@ def create_table(self, full_name: str, klass: Dataclass):
     def _schema_for(cls, klass: Dataclass):
         fields = []
         for f in dataclasses.fields(klass):
-            field_type = f.type
-            # workaround rare (Python?) issue where f.type is the type name instead of the type itself
-            # this seems to happen when the dataclass is first used from a file importing it
-            if isinstance(field_type, str):
-                try:
-                    field_type = __builtins__[field_type]
-                except TypeError as e:
-                    logger.warning(f"Could not load type {field_type}", exc_info=e)
+            field_type = cls._field_type(f)
             if isinstance(field_type, UnionType):
                 field_type = field_type.__args__[0]
             if field_type not in cls._builtin_type_mapping:
@@ -89,6 +82,17 @@ def _schema_for(cls, klass: Dataclass):
             fields.append(f"{f.name} {spark_type}{not_null}")
         return ", ".join(fields)
 
+    @classmethod
+    def _field_type(cls, field: dataclasses.Field):
+        # workaround rare (Python?) issue where f.type is the type name instead of the type itself
+        # this seems to happen when the dataclass is first used from a file importing it
+        if isinstance(field.type, str):
+            try:
+                return __builtins__[field.type]
+            except TypeError as e:
+                logger.warning(f"Could not load type {field.type}", exc_info=e)
+        return field.type
+
     @classmethod
     def _filter_none_rows(cls, rows, klass):
         if len(rows) == 0:
@@ -168,12 +172,12 @@ def save_table(self, full_name: str, rows: Sequence[DataclassInstance], klass: D
             sql = f'INSERT INTO {full_name} ({", ".join(field_names)}) VALUES ({vals})'
             self.execute(sql)
 
-    @staticmethod
-    def _row_to_sql(row: DataclassInstance, fields: tuple[dataclasses.Field[Any], ...]):
+    @classmethod
+    def _row_to_sql(cls, row: DataclassInstance, fields: tuple[dataclasses.Field[Any], ...]):
         data = []
         for f in fields:
             value = getattr(row, f.name)
-            field_type = f.type
+            field_type = cls._field_type(f)
             if isinstance(field_type, UnionType):
                 field_type = field_type.__args__[0]
             if value is None: