Nullable required fields should not have default value by raymondbutcher · Pull Request #2520 · koxudaxi/datamodel-code-generator

raymondbutcher · 2025-10-17T15:27:04Z

Hi. Thanks for the project!

My OpenAPI spec has some fields as both nullable and required, but they are generating models with default values like this:

class Person(BaseModel):
    first_name: Annotated[str | None, Field(alias='firstName')] = None
    last_name: Annotated[str | None, Field(alias='lastName')] = None

Those default values make the fields optional, so it's not working as expected.

This fix also highlighted what looks to be a bug in an existing test that is checking for an incorrect result:

JSON spec has two required fields:
- https://github.com/koxudaxi/datamodel-code-generator/blob/main/tests/data/jsonschema/null_and_array.json
Expected Pydantic V1 model looks good, both fields must be provided:
- https://github.com/koxudaxi/datamodel-code-generator/blob/main/tests/data/expected/main/jsonschema/null_and_array.py
Expected Pydantic V2 model looks wrong, one field has a default value so can be omitted:
- https://github.com/koxudaxi/datamodel-code-generator/blob/main/tests/data/expected/main/jsonschema/null_and_array_v2.py

Summary by CodeRabbit

Bug Fixes
- Stricter handling of default-value assignment for optional/nullable fields; some optional fields no longer receive an implicit None default.
New Features
- Improved OpenAPI/model generation for nullable-but-required fields using annotations; adds a Person schema example.
Documentation
- Updated Pydantic v2 example to reflect new optional-field defaults.
Tests
- Added tests for nullable-required field generation (duplicate test entry present).

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ilovelinux · 2025-10-31T14:57:00Z

This PR closes the following issues:

[BUG]: All of the fields have a None default #2040

Please link this PR with the issue as described here. Thanks!

…del.jinja2 Co-authored-by: Antonio Spadaro <[email protected]>

codspeed-hq · 2025-11-03T14:10:03Z

CodSpeed Performance Report

Merging #2520 will not alter performance

_{Comparing raymondbutcher:required-nullable-annotated (bc8895a) with main (590e568)}

Summary

✅ 52 untouched
⏩ 10 skipped¹

10 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. ↩

koxudaxi · 2025-11-12T17:18:21Z

@raymondbutcher
Thank you for creating the PR.
Could you plesae fix the unittest ?

    raise rewrite_traceback_stack(source=source)
  File "/Users/runner/work/datamodel-code-generator/datamodel-code-generator/.tox/3.11/lib/python3.11/site-packages/datamodel_code_generator/model/template/pydantic_v2/BaseModel.jinja2", line 35, in template
    {%- if not field.required and (field.represented_default != 'None' or not field.strip_default_none) or field.data_type.is_optional)
    ^^^^^^^^^^^^^^^^^^^^^^^^^
jinja2.exceptions.TemplateSyntaxError: unexpected ')'```

codecov · 2025-11-29T13:43:19Z

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.33%. Comparing base (590e568) to head (bc8895a).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2520   +/-   ##
=======================================
  Coverage   99.33%   99.33%           
=======================================
  Files          81       81           
  Lines       11478    11480    +2     
  Branches     1367     1367           
=======================================
+ Hits        11402    11404    +2     
  Misses         45       45           
  Partials       31       31

Flag	Coverage Δ
unittests	`99.33% <100.00%> (+<0.01%)`	⬆️

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coderabbitai · 2025-12-18T15:36:22Z

Walkthrough

Tightened the Pydantic v2 BaseModel template default-emission condition; removed several emitted = None defaults in generated fixtures; added an OpenAPI schema, its generated model using Annotated, and a test (duplicated in the diff).

Changes

Cohort / File(s)	Summary
Template logic update `src/datamodel_code_generator/model/template/pydantic_v2/BaseModel.jinja2`	Tightened the conditional that decides when to emit a field default. Now requires `not field.has_default_factory_in_field` and `not field.required`, and only emits defaults when `(field.represented_default != 'None' or not field.strip_default_none or field.data_type.is_optional)`.
Removed explicit None defaults `tests/data/expected/main/jsonschema/null_and_array_v2.py`, `tests/data/expected/main/openapi/unquoted_null.py`, `docs/cli-reference/model-customization.md`	Removed `= None` defaults from optional field declarations (e.g., `list[Any]
New OpenAPI schema `tests/data/openapi/nullable_required_annotated.yaml`	Added `Person` schema with `firstName` and `lastName` marked `nullable: true` and included in `required`.
New generated model `tests/data/expected/main/openapi/nullable_required_annotated.py`	Added Pydantic v2 model `Person` using `Annotated[str
Test additions `tests/main/openapi/test_main_openapi.py`	Added `test_main_openapi_nullable_required_annotated` to validate generation with options (`pydantic_v2.BaseModel`, `--strict-nullable`, `--use-annotated`, `--use-union-operator`, `--snake-case-field`). The function appears duplicated in the diff.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~25 minutes

Inspect BaseModel.jinja2 conditional logic for edge cases: optional unions, strip_default_none, and default factories.
Verify generated files (tests/data/expected/...) reflect intended semantics and imports for Annotated/Field.
Remove or consolidate the duplicated test in tests/main/openapi/test_main_openapi.py.
Confirm documentation example in docs/cli-reference/model-customization.md matches template output.

Poem

🐰
I nibble at templates, tighten a seam,
Defaults sit straighter, neat as a dream.
Nullable blooms now stand on their own,
New models and tests in the burrow are shown,
A carrot-code hop — light, quick, and keen! 🥕

Pre-merge checks and finishing touches

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The pull request title accurately summarizes the main change: preventing nullable required fields from having default values, which directly addresses the core issue in the changeset.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.

✨ Finishing touches

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📥 Commits

Reviewing files that changed from the base of the PR and between 02a50d3 and d0913e1.

📒 Files selected for processing (1)

docs/cli-reference/model-customization.md (1 hunks)

🔇 Additional comments (1)

docs/cli-reference/model-customization.md (1)

3154-3154: Documentation correctly reflects required nullable field fix.

The change aligns with the PR objective: required nullable fields no longer receive default values. In Pydantic v2, the field items (marked as required despite accepting null) is now correctly generated without = None, making it a true required field at the type level.

However, verify that the Pydantic v1 output (lines 3131-3132) is also consistent—it shows items: list[Any] | None without a default, which is correct for a required field.

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koxudaxi · 2025-12-18T16:17:38Z

@coderabbitai review

coderabbitai · 2025-12-18T16:17:43Z

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koxudaxi · 2025-12-18T19:14:22Z

@ilovelinux Can you review the PR again?

coderabbitai · 2025-12-18T19:18:11Z

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Review triggered.

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…ted' into required-nullable-annotated

LGTM

Paillat-dev · 2025-12-20T11:30:25Z

Thank You !

raymondbutcher and others added 2 commits October 17, 2025 16:07

fix: nullable required fields should not have default value

d72db00

[pre-commit.ci] auto fixes from pre-commit.com hooks

4c52967

for more information, see https://pre-commit.ci

ilovelinux requested changes Oct 31, 2025

View reviewed changes

Comment thread src/datamodel_code_generator/model/template/pydantic_v2/BaseModel.jinja2 Outdated

gaborbernat and others added 2 commits November 3, 2025 06:06

Update src/datamodel_code_generator/model/template/pydantic_v2/BaseMo…

dd8e0a8

…del.jinja2 Co-authored-by: Antonio Spadaro <[email protected]>

Merge branch 'main' into required-nullable-annotated

1f9869e

gaborbernat enabled auto-merge (squash) November 3, 2025 14:07

ilovelinux previously requested changes Nov 16, 2025

View reviewed changes

Comment thread src/datamodel_code_generator/model/template/pydantic_v2/BaseModel.jinja2 Outdated

ilovelinux linked an issue Nov 17, 2025 that may be closed by this pull request

[BUG]: All of the fields have a None default #2040

Closed

koxudaxi added 2 commits November 29, 2025 22:23

fix: update condition for default value assignment in BaseModel template

40b418b

Merge branch 'main' into required-nullable-annotated

a4d26d3

koxudaxi requested a review from ilovelinux November 29, 2025 13:44

koxudaxi and others added 6 commits November 30, 2025 16:29

Merge branch 'main' into required-nullable-annotated

eb05935

Merge branch 'main' into required-nullable-annotated

52c9b92

Merge branch 'main' into required-nullable-annotated

c23fa2f

Merge branch 'main' into required-nullable-annotated

b760b64

Merge branch 'main' into required-nullable-annotated

32345b2

Merge main into required-nullable-annotated

17c30ba

Merge branch 'main' into required-nullable-annotated

20585c4

koxudaxi added 3 commits December 19, 2025 03:24

Merge branch 'main' into required-nullable-annotated

b6e1572

Merge branch 'main' into required-nullable-annotated

a6206ce

Merge branch 'main' into required-nullable-annotated

1dbc102

koxudaxi added 4 commits December 19, 2025 23:09

Merge origin/main into required-nullable-annotated

8fdac6d

Merge remote-tracking branch 'raymondbutcher/required-nullable-annota…

02a50d3

…ted' into required-nullable-annotated

Remove default value for 'items' in MyObjItem class

d0913e1

Merge branch 'main' into required-nullable-annotated

980cc90

koxudaxi added the safe-to-fix label Dec 20, 2025

Merge branch 'main' into required-nullable-annotated

bc8895a

gaborbernat merged commit 4423a49 into koxudaxi:main Dec 20, 2025
38 checks passed

coderabbitai Bot mentioned this pull request Jan 12, 2026

Fix required list fields ignoring empty default values #2958

Merged

coderabbitai Bot mentioned this pull request Feb 14, 2026

Fix missing | None for nullable enum literals in TypedDict #2991

Merged

coderabbitai Bot mentioned this pull request Feb 25, 2026

Generated code uses Optional without importing it (with use_annotated=True + disable_future_imports=True) #3008

Closed

This was referenced Mar 11, 2026

Default values for required fields are sometimes rendered and sometimes not #3048

Closed

Fix required field default rendering and --use-default nullable types #3054

Merged

coderabbitai Bot mentioned this pull request Apr 2, 2026

Use Field(default=value) instead of Field(value) #3069

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