From b9de23c992d0243f11915cc9badeda39da520b5d Mon Sep 17 00:00:00 2001
From: Anas Khan <83116240+anxkhn@users.noreply.github.com>
Date: Sat, 4 Jul 2026 18:25:47 +0530
Subject: [PATCH] fix: preserve write_default when applying a name mapping

NameMappingProjectionVisitor.field rebuilt each NestedField with an
initial_write= keyword, but NestedField.__init__ has no such parameter
(the write-default keyword is write_default). Being a Pydantic model,
the unknown key was swallowed by **data and silently ignored, so
apply_name_mapping dropped every field's write_default to None.

Pass write_default= to match the NestedField constructor and add a
regression test asserting both initial_default and write_default
survive a name mapping.
---
 pyiceberg/table/name_mapping.py  |  2 +-
 tests/table/test_name_mapping.py | 19 +++++++++++++++++++
 2 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/pyiceberg/table/name_mapping.py b/pyiceberg/table/name_mapping.py
index 1cf6bc0106..bd8b8529c5 100644
--- a/pyiceberg/table/name_mapping.py
+++ b/pyiceberg/table/name_mapping.py
@@ -341,7 +341,7 @@ def field(self, field: NestedField, field_partner: MappedField | None, field_res
             required=field.required,
             doc=field.doc,
             initial_default=field.initial_default,
-            initial_write=field.write_default,
+            write_default=field.write_default,
         )
 
     def list(self, list_type: ListType, list_partner: MappedField | None, element_result: IcebergType) -> IcebergType:
diff --git a/tests/table/test_name_mapping.py b/tests/table/test_name_mapping.py
index e8de5f18e5..073e893455 100644
--- a/tests/table/test_name_mapping.py
+++ b/tests/table/test_name_mapping.py
@@ -403,3 +403,22 @@ def test_mapping_using_by_visitor(table_schema_nested: Schema, table_name_mappin
         ),
     )
     assert apply_name_mapping(schema_without_ids, table_name_mapping_nested).fields == table_schema_nested.fields
+
+
+def test_mapping_preserves_field_defaults() -> None:
+    schema_without_ids = Schema(
+        NestedField(
+            field_id=0,
+            name="foo",
+            field_type=StringType(),
+            required=False,
+            initial_default="init",
+            write_default="write",
+        ),
+    )
+    name_mapping = NameMapping([MappedField(field_id=1, names=["foo"])])
+
+    mapped_field = apply_name_mapping(schema_without_ids, name_mapping).fields[0]
+
+    assert mapped_field.initial_default == "init"
+    assert mapped_field.write_default == "write"