[BUG] Fix Patch operations reset fields to default if not specified #23650

[swapneswarsundarray]

Fixes #23650

Problem

In the Python generator, PATCH models were sending default values even when fields were not explicitly set by the client. This caused unintended updates where fields were reset to defaults.

Root Cause

The generated to_dict() method uses exclude_none=True, which only skips None values but still includes fields with default values.

Solution

Use exclude_unset=True for PATCH models so that only explicitly set fields are included in the payload. Non-PATCH models continue using exclude_none=True to avoid breaking existing behavior.

Changes

• Updated model_generic.mustache to conditionally use exclude_unset=True for PATCH models
• Added logic in PythonClientCodegen to detect PATCH models (based on naming convention) and set a flag

Impact

PATCH requests now send only modified fields, preventing unintended resets. Behavior for non-PATCH models remains unchanged.

PR checklist

• Read the contribution guidelines.
• Pull Request title clearly describes the work in the pull request and Pull Request description provides details about how to validate the work. Missing information here may result in delayed response from the community.
• Run the following to build the project and update samples:

  ./mvnw clean package || exit
  ./bin/generate-samples.sh ./bin/configs/*.yaml || exit
  ./bin/utils/export_docs_generators.sh || exit
  

  (For Windows users, please run the script in WSL)
  Commit all changed files.
  This is important, as CI jobs will verify all generator outputs of your HEAD commit as it would merge with master.
  These must match the expectations made by your contribution.
  You may regenerate an individual generator by passing the relevant config(s) as an argument to the script, for example ./bin/generate-samples.sh bin/configs/java*.
  IMPORTANT: Do NOT purge/delete any folders/files (e.g. tests) when regenerating the samples as manually written tests may be removed.
• File the PR against the correct branch: master (upcoming 7.x.0 minor release - breaking changes with fallbacks), 8.0.x (breaking changes without fallbacks)
• If your PR solves a reported issue, reference it using GitHub's linking syntax (e.g., having "fixes #123" present in the PR description)
• If your PR is targeting a particular programming language, @mention the technical committee members, so they are more likely to review the pull request.

---

Summary by cubic

Fixes #23650. Python PATCH models now send only explicitly set fields for classes prefixed with Patched, preventing defaults from overwriting existing data; non-PATCH behavior is unchanged. Also fixes template formatting to avoid broken Python output.

• Bug Fixes
  • In model_generic.mustache, use inline conditional args in model_dump(...): exclude_unset=True for vendorExtensions.isPatchedModel, otherwise exclude_none=True.
  • In PythonClientCodegen#postProcessModels, mark Patched* models with isPatchedModel for template handling.

^{Written for commit 2d3bd2e. Summary will update on new commits.}

[cubic-dev-ai]

No issues found across 2 files