Nullable required fields should not have default value

[raymondbutcher]

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

[ilovelinux]

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!

[codspeed-hq]

CodSpeed Performance Report

Merging #2520 will not alter performance

_{Comparing raymondbutcher:required-nullable-annotated (c23fa2f) with main (000b177)}

Summary

✅ 30 untouched
⏩ 3 skipped¹

Footnotes

1. 3 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]

@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 ')'```

[ilovelinux]

My fault, I forgot a parenthesis.
Should fix #2520 (comment)

Please check the logic compared to your original proposal

Suggested change

	{%- if not field.required and (field.represented_default != 'None' or not field.strip_default_none) or field.data_type.is_optional)
	{%- if not field.required and (field.represented_default != 'None' or not field.strip_default_none or field.data_type.is_optional)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.59%. Comparing base (000b177) to head (c23fa2f).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2520   +/-   ##
=======================================
  Coverage   99.59%   99.59%           
=======================================
  Files          73       73           
  Lines        7742     7744    +2     
  Branches      905      905           
=======================================
+ Hits         7711     7713    +2     
  Misses         14       14           
  Partials       17       17           

Flag	Coverage Δ
unittests	99.59% <100.00%> (+<0.01%)	⬆️

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