Add serializer for AssertRefSnapshotId allowing null json value

pyiceberg/table/update/__init__.py

@@ -21,9 +21,9 @@
 from abc import ABC, abstractmethod
 from datetime import datetime
 from functools import singledispatch
-from typing import TYPE_CHECKING, Annotated, Any, Dict, Generic, List, Literal, Optional, Set, Tuple, TypeVar, Union, cast
+from typing import TYPE_CHECKING, Annotated, Any, Dict, Generic, List, Literal, Optional, Tuple, TypeVar, Union, cast
 
-from pydantic import Field, field_validator, model_validator
+from pydantic import Field, field_validator, model_validator, model_serializer
 
 from pyiceberg.exceptions import CommitFailedException
 from pyiceberg.partitioning import PARTITION_FIELD_ID_START, PartitionSpec
@@ -727,6 +727,14 @@ class AssertRefSnapshotId(ValidatableTableRequirement):
     ref: str = Field(...)
     snapshot_id: Optional[int] = Field(default=None, alias="snapshot-id")
 
+    @model_serializer
+    def ser_model(self) -> dict[str, Any]:
+        return {
+            "type": self.type,
+            "ref": self.ref,
+            "snapshot-id": self.snapshot_id,
+        }
+
     def validate(self, base_metadata: Optional[TableMetadata]) -> None:
         if base_metadata is None:
             raise CommitFailedException("Requirement failed: current table metadata is missing")
@@ -745,13 +753,6 @@ def validate(self, base_metadata: Optional[TableMetadata]) -> None:
         elif self.snapshot_id is not None:
             raise CommitFailedException(f"Requirement failed: branch or tag {self.ref} is missing, expected {self.snapshot_id}")
 
-    # override the override method, allowing None to serialize to `null` instead of being omitted.
-    def model_dump_json(
-        self, exclude_none: bool = False, exclude: Optional[Set[str]] = None, by_alias: bool = True, **kwargs: Any
-    ) -> str:
-        # `snapshot-id` is required in json response, even if null
-        return super().model_dump_json(exclude_none=False)
-
 
 class AssertLastAssignedFieldId(ValidatableTableRequirement):
     """The table's last assigned column id must match the requirement's `last-assigned-field-id`."""

tests/test_serializers.py

@@ -18,14 +18,16 @@
 import json
 import os
 import uuid
-from typing import Any, Dict
+from typing import Any, Dict, Tuple
 
 import pytest
 from pytest_mock import MockFixture
 
 from pyiceberg.serializers import ToOutputFile
 from pyiceberg.table import StaticTable
 from pyiceberg.table.metadata import TableMetadataV1
+from pyiceberg.table.update import AssertRefSnapshotId, TableRequirement
+from pyiceberg.typedef import IcebergBaseModel
 
 
 def test_legacy_current_snapshot_id(
@@ -48,3 +50,13 @@ def test_legacy_current_snapshot_id(
     backwards_compatible_static_table = StaticTable.from_metadata(metadata_location)
     assert backwards_compatible_static_table.metadata.current_snapshot_id is None
     assert backwards_compatible_static_table.metadata == static_table.metadata
+
+
+def test_null_serializer_field() -> None:
+    class ExampleRequest(IcebergBaseModel):
+        requirements: Tuple[TableRequirement, ...]
+
+    request = ExampleRequest(requirements=(AssertRefSnapshotId(ref="main", snapshot_id=None),))
+    dumped_json = request.model_dump_json()
+    expected_json = """{"type":"assert-ref-snapshot-id","ref":"main","snapshot-id":null}"""
+    assert expected_json in dumped_json