Fix optional discriminator literals by koxudaxi · Pull Request #3608 · koxudaxi/datamodel-code-generator

koxudaxi · 2026-07-16T15:48:33Z

Fixes: #3606

Summary by CodeRabbit

Bug Fixes
- Improved Pydantic v2 discriminated unions when required fields are forced to be optional, including correct discriminator defaulting and null/required behavior.
- Preserved correct generation for both standard models and dataclass outputs, with better handling when discriminator types collapse to a single literal/enum member.
Tests
- Added OpenAPI generation fixtures and assertions covering discriminator optionality, enum-value discriminator usage, and integer enum mappings.
- Added dynamic model validation coverage for forced-optional discriminator literals.

coderabbitai · 2026-07-16T15:48:41Z

No actionable comments were generated in the recent review. 🎉

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📥 Commits

Reviewing files that changed from the base of the PR and between e64bc09 and 0a4370a.

⛔ Files ignored due to path filters (2)

tests/data/expected/dynamic_models/force_optional_discriminator_literals.json is excluded by !tests/data/**/*.json and included by none
tests/data/openapi/discriminator_force_optional.yaml is excluded by !tests/data/**/*.yaml and included by none

📒 Files selected for processing (7)

src/datamodel_code_generator/parser/base.py
tests/data/expected/main/openapi/discriminator/enum_single_value_anyof_use_enum_force_optional.py
tests/data/expected/main/openapi/discriminator/force_optional_pydantic_v2_dataclass.py
tests/data/expected/main/openapi/discriminator/integer_mapping_use_enum_force_optional.py
tests/main/openapi/test_main_openapi.py
tests/main/test_dynamic_models.py
tox.ini

🚧 Files skipped from review as they are similar to previous changes (2)

tests/data/expected/main/openapi/discriminator/force_optional_pydantic_v2_dataclass.py
tests/main/test_dynamic_models.py

📝 Walkthrough

Walkthrough

Changes

The parser now assigns literal or enum-member defaults to forced-optional Pydantic v2 discriminator fields while preserving non-nullable Literal types. Generated fixtures and tests cover base models, dataclasses, enum mappings, dynamic generation, and OpenAPI output.

Optional discriminator handling

Layer / File(s)	Summary
Apply optional discriminator defaults `src/datamodel_code_generator/parser/base.py`	Discriminator defaults are resolved from single literals or enum members; matching Pydantic v2 fields become non-required and non-nullable while msgspec handling remains separate.
Generate discriminator model outputs `tests/data/expected/main/openapi/discriminator/*`	Expected Pydantic v2 base-model, dataclass, enum, integer-mapping, and optional-union outputs reflect literal discriminator defaults.
Validate discriminator generation `tests/main/test_dynamic_models.py`, `tests/main/openapi/test_main_openapi.py`, `tox.ini`	Dynamic-model and OpenAPI tests validate generated models and golden files, with the new tests registered in the Pydantic test environment.

Estimated code review effort: 3 (Moderate) | ~25 minutes

Possibly related PRs

koxudaxi/datamodel-code-generator#3070: Both modify discriminator literal handling in Parser.__apply_discriminator_type().
koxudaxi/datamodel-code-generator#3074: Both modify discriminator mapping and literal-value resolution.
koxudaxi/datamodel-code-generator#3411: Both adjust Pydantic v2 discriminator-field generation in the same code path.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	Concise, specific, and matches the main fix for optional discriminator literals.
Linked Issues check	✅ Passed	The parser fix and added Pydantic v2 tests directly address the discriminator-needs-literal failure under force_optional_for_required_fields.
Out of Scope Changes check	✅ Passed	The changes are centered on the discriminator optionality bug and its tests; no unrelated features appear in the summary.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.

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Commit unit tests in branch agent/fix-optional-discriminator-literals

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github-actions · 2026-07-16T15:50:22Z

📚 Docs Preview: https://pr-3608.datamodel-code-generator.pages.dev

codspeed-hq · 2026-07-16T15:52:54Z

Merging this PR will not alter performance

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✅ 13 untouched benchmarks
⏩ 98 skipped benchmarks¹

_{Comparing agent/fix-optional-discriminator-literals (0a4370a) with main (eb65a56)}

98 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

coderabbitai

Actionable comments posted: 1

🧹 Nitpick comments (1)

src/datamodel_code_generator/parser/base.py (1)
2045-2052: 📐 Maintainability & Code Quality | 🔵 Trivial | 💤 Low value

Update the type hint to accept Enum members.

To cleanly support using Enum values as the discriminator default when use_enum_values_in_discriminator=True, literal should also accept Member.
♻️ Proposed refactor
     def __set_force_optional_discriminator_literal_default(
         self,
         model: DataModel,
         discriminator_field: DataModelFieldBase,
-        literal: DiscriminatorValue,
+        literal: DiscriminatorValue | Member,
         *,
         can_retain_cache: bool,
     ) -> None:
🤖 Prompt for AI Agents
Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@src/datamodel_code_generator/parser/base.py` around lines 2045 - 2052, Update
the literal parameter type hint in
__set_force_optional_discriminator_literal_default to accept Enum Member values
in addition to DiscriminatorValue, preserving the existing behavior and other
parameter types.

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@src/datamodel_code_generator/parser/base.py`:
- Around line 2152-2171: Update the discriminator resolution flow around
_is_msgspec_struct and replace_field_type: only take the early-break path for
msgspec structs, preserving replace_field_type and discriminator_field.required
updates for Pydantic v2 models. Move
__set_force_optional_discriminator_literal_default to after the
replace_field_type block so it runs for every resolved Pydantic discriminator
field, including fields whose literals were inferred from a non-literal schema.

---

Nitpick comments:
In `@src/datamodel_code_generator/parser/base.py`:
- Around line 2045-2052: Update the literal parameter type hint in
__set_force_optional_discriminator_literal_default to accept Enum Member values
in addition to DiscriminatorValue, preserving the existing behavior and other
parameter types.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

Push a commit to this branch (recommended)
Create a new PR with the fixes

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Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

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Run ID: f0b500ac-7e2c-4ef9-b39e-6a8cd7a7cf63

📥 Commits

Reviewing files that changed from the base of the PR and between 5381743 and e64bc09.

⛔ Files ignored due to path filters (2)

tests/data/expected/dynamic_models/force_optional_discriminator_literals.json is excluded by !tests/data/**/*.json and included by none
tests/data/openapi/discriminator_force_optional.yaml is excluded by !tests/data/**/*.yaml and included by none

📒 Files selected for processing (7)

src/datamodel_code_generator/parser/base.py
tests/data/expected/main/openapi/discriminator/force_optional_pydantic_v2.py
tests/data/expected/main/openapi/discriminator/force_optional_pydantic_v2_dataclass.py
tests/data/expected/main/openapi/discriminator/required_pydantic_v2.py
tests/main/openapi/test_main_openapi.py
tests/main/test_dynamic_models.py
tox.ini

codecov · 2026-07-16T16:03:23Z

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (5381743) to head (0a4370a).
⚠️ Report is 4 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main     #3608   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          164       164           
  Lines        35647     35725   +78     
  Branches      4106      4121   +15     
=========================================
+ Hits         35647     35725   +78

Flag	Coverage Δ
unittests	`100.00% <100.00%> (ø)`

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Fix optional discriminator literals

e64bc09

koxudaxi marked this pull request as ready for review July 16, 2026 15:49

Stabilize discriminator snapshots

1d8d2cc

coderabbitai Bot reviewed Jul 16, 2026

View reviewed changes

Comment thread src/datamodel_code_generator/parser/base.py

Handle inferred discriminator literals

0a4370a

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Fix optional discriminator literals#3608

Fix optional discriminator literals#3608
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