Fix missing Field import with multiple aliases on required fields

[koxudaxi]

Fixes: #2989

Summary by CodeRabbit

Release Notes

• New Features
  • Added support for multiple validation aliases on required fields in Pydantic v2 models. Fields can now accept data using any of several alternative names through the AliasChoices mechanism.

[coderabbitai]

📝 Walkthrough

Walkthrough

Removed a fast-path optimization in BaseModel.imports that skipped adding the Field import for simple, non-aliased, non-nullable, non-constrained fields. Field import is now always included when field representation is present, ensuring it's available when aliases create AliasChoices requirements.

Changes

Cohort / File(s)	Summary
Base Model Import Logic src/datamodel_code_generator/model/pydantic/base_model.py	Removed conditional fast-path that bypassed Field import for simple fields; now deterministically adds Field import whenever self.field is present.
Test Data — Dynamic Models tests/data/expected/dynamic_models/multiple_aliases_required_code.py	New expected output file showing Customer class with full_name field using AliasChoices for multiple validation aliases on a required field.
Test Data — JSON Schema tests/data/expected/main/jsonschema/jsonschema_multiple_aliases_required_pydantic_v2.py	New expected output file showing Root model with two fields using AliasChoices for multiple validation aliases in Pydantic v2.
Test Cases tests/main/jsonschema/test_main_jsonschema.py, tests/main/test_dynamic_models.py	Added three new test cases validating multiple aliases on required fields: one for JSON schema main generation and two for dynamic model generation (snapshot and code output variants).

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Suggested labels

breaking-change-analyzed

Poem

🐰 A field was missing, lost without a trace,
When aliases made AliasChoices take their place,
No more the shortcut steals the import's light—
Now Field appears when needed, always right! ✨

🚥 Pre-merge checks | ✅ 6

✅ Passed checks (6 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly summarizes the main fix: addressing a missing Field import when multiple aliases are used with required fields, which directly aligns with the changeset.
Linked Issues check	✅ Passed	The PR successfully fixes issue #2989 by removing the early fast-path in BaseModel.imports that was skipping Field import for certain field types, ensuring Field is always included when needed for AliasChoices.
Out of Scope Changes check	✅ Passed	All changes are directly scoped to fixing the missing Field import issue: core logic fix, expected test output files, and comprehensive test coverage with no unrelated modifications.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.
Merge Conflict Detection	✅ Passed	✅ No merge conflicts detected when merging into main

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✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch fix/multiple-aliases-required-field-import

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[github-actions]

📚 Docs Preview: https://pr-2992.datamodel-code-generator.pages.dev

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (b58970a) to head (e863084).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main     #2992   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           94        94           
  Lines        18051     18061   +10     
  Branches      2091      2090    -1     
=========================================
+ Hits         18051     18061   +10     

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

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[github-actions]

Breaking Change Analysis

Result: No breaking changes detected

Reasoning: This PR is a bug fix that adds the missing Field import when validation_aliases (AliasChoices) is used on required fields in Pydantic v2. Previously, the code would generate Field(..., validation_alias=AliasChoices(...)) but fail to include Field in the imports, causing runtime NameError. The generated code structure and behavior remain unchanged - this simply ensures the import statement matches what the code generator produces. No API, CLI, templates, or default behaviors are modified.

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This analysis was performed by Claude Code Action

[github-actions]

🎉 Released in 0.54.0

This PR is now available in the latest release. See the release notes for details.