Fix dataset serialization when inputs have discriminators with defaults (#3079)

Author: DouweM

docs/evals.md

@@ -653,10 +653,12 @@ async def main():
     print(output_file.read_text())
     """
     # yaml-language-server: $schema=questions_cases_schema.json
+    name: null
     cases:
     - name: Easy Capital Question
       inputs:
         question: What is the capital of France?
+        context: null
       metadata:
         difficulty: easy
         category: Geography
@@ -668,6 +670,7 @@ async def main():
     - name: Challenging Landmark Question
       inputs:
         question: Which world-famous landmark is located on the banks of the Seine River?
+        context: null
       metadata:
         difficulty: hard
         category: Landmarks
@@ -676,6 +679,7 @@ async def main():
         confidence: 0.9
       evaluators:
       - EqualsExpected
+    evaluators: []
     """
 ```
 
@@ -713,11 +717,13 @@ async def main():
     """
     {
       "$schema": "questions_cases_schema.json",
+      "name": null,
       "cases": [
         {
           "name": "Easy Capital Question",
           "inputs": {
-            "question": "What is the capital of France?"
+            "question": "What is the capital of France?",
+            "context": null
           },
           "metadata": {
             "difficulty": "easy",
@@ -734,7 +740,8 @@ async def main():
         {
           "name": "Challenging Landmark Question",
           "inputs": {
-            "question": "Which world-famous landmark is located on the banks of the Seine River?"
+            "question": "Which world-famous landmark is located on the banks of the Seine River?",
+            "context": null
           },
           "metadata": {
             "difficulty": "hard",
@@ -748,7 +755,8 @@ async def main():
             "EqualsExpected"
           ]
         }
-      ]
+      ],
+      "evaluators": []
     }
     """
 ```

pydantic_evals/pydantic_evals/dataset.py

@@ -646,15 +646,15 @@ def to_file(
 
         context: dict[str, Any] = {'use_short_form': True}
         if fmt == 'yaml':
-            dumped_data = self.model_dump(mode='json', by_alias=True, exclude_defaults=True, context=context)
+            dumped_data = self.model_dump(mode='json', by_alias=True, context=context)
             content = yaml.dump(dumped_data, sort_keys=False)
             if schema_ref:  # pragma: no branch
                 yaml_language_server_line = f'{_YAML_SCHEMA_LINE_PREFIX}{schema_ref}'
                 content = f'{yaml_language_server_line}\n{content}'
             path.write_text(content)
         else:
             context['$schema'] = schema_ref
-            json_data = self.model_dump_json(indent=2, by_alias=True, exclude_defaults=True, context=context)
+            json_data = self.model_dump_json(indent=2, by_alias=True, context=context)
             path.write_text(json_data + '\n')
 
     @classmethod
@@ -724,6 +724,7 @@ class Case(BaseModel, extra='forbid'):  # pyright: ignore[reportUnusedClass]  #
                 evaluators: list[Union[tuple(evaluator_schema_types)]] = []  # pyright: ignore  # noqa UP007
 
         class Dataset(BaseModel, extra='forbid'):
+            name: str | None = None
             cases: list[Case]
             if evaluator_schema_types:  # pragma: no branch
                 evaluators: list[Union[tuple(evaluator_schema_types)]] = []  # pyright: ignore  # noqa UP007

tests/evals/test_dataset.py

@@ -4,7 +4,7 @@
 import sys
 from dataclasses import dataclass, field
 from pathlib import Path
-from typing import Any
+from typing import Any, Literal
 
 import pytest
 import yaml
@@ -863,6 +863,38 @@ async def test_serialization_to_json(example_dataset: Dataset[TaskInput, TaskOut
     assert (tmp_path / schema).exists()
 
 
+def test_serializing_parts_with_discriminators(tmp_path: Path):
+    class Foo(BaseModel):
+        foo: str
+        kind: Literal['foo'] = 'foo'
+
+    class Bar(BaseModel):
+        bar: str
+        kind: Literal['bar'] = 'bar'
+
+    items = [Foo(foo='foo'), Bar(bar='bar')]
+
+    dataset = Dataset[list[Foo | Bar]](cases=[Case(inputs=items)])
+    yaml_path = tmp_path / 'test_cases.yaml'
+    dataset.to_file(yaml_path)
+
+    loaded_dataset = Dataset[list[Foo | Bar]].from_file(yaml_path)
+    assert loaded_dataset == snapshot(
+        Dataset(
+            name='test_cases',
+            cases=[
+                Case(
+                    name=None,
+                    inputs=[
+                        Foo(foo='foo'),
+                        Bar(bar='bar'),
+                    ],
+                )
+            ],
+        )
+    )
+
+
 def test_serialization_errors(tmp_path: Path):
     with pytest.raises(ValueError) as exc_info:
         Dataset[TaskInput, TaskOutput, TaskMetadata].from_file(tmp_path / 'test_cases.abc')