Allow snapshot-id in assert-ref-snapshot-id requirement to serialize to null in json, fix #2342

Author: ox

pyiceberg/table/update/__init__.py

@@ -736,7 +736,7 @@ class AssertRefSnapshotId(ValidatableTableRequirement):
 
     type: Literal["assert-ref-snapshot-id"] = Field(default="assert-ref-snapshot-id")
     ref: str = Field(...)
-    snapshot_id: Optional[int] = Field(default=None, alias="snapshot-id")
+    snapshot_id: Optional[int] = Field(default=None, alias="snapshot-id", exclude=False)
 
     def validate(self, base_metadata: Optional[TableMetadata]) -> None:
         if base_metadata is None:
@@ -756,6 +756,13 @@ 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:
+        return super().model_dump_json(
+            exclude_none=exclude_none, exclude=self._exclude_private_properties(exclude), by_alias=by_alias, **kwargs
+        )
 
 class AssertLastAssignedFieldId(ValidatableTableRequirement):
     """The table's last assigned column id must match the requirement's `last-assigned-field-id`."""

tests/table/test_init.py

@@ -1039,6 +1039,11 @@ def test_assert_ref_snapshot_id(table_v2: Table) -> None:
     ):
         AssertRefSnapshotId(ref="test", snapshot_id=3055729675574597004).validate(base_metadata)
 
+    expected_json = """{"type":"assert-ref-snapshot-id","ref":"main","snapshot-id":null}"""
+    assert_json = AssertRefSnapshotId(ref="main").model_dump_json()
+    print(assert_json)
+    assert assert_json == expected_json
+
 
 def test_assert_last_assigned_field_id(table_v2: Table) -> None:
     base_metadata = table_v2.metadata