Pydantic [docs]: cannot leverage on alias

The Fix

pip install pydantic==1.10.17

Based on closed pydantic/pydantic issue #9678 · PR/commit linked

Production note: Most teams hit this during upgrades or environment changes. Roll out with a canary and smoke critical endpoints (health, OpenAPI/docs) before 100%.

Jump to Verify Open PR/Commit

@@ -145,10 +145,8 @@ print(user.model_dump(by_alias=True))  # (2)!
     over `alias` for serialization.
 
-    You may also set `alias_priority` on a field to change this behavior.
-
-    You can read more about [Alias Precedence](../concepts/alias.md#alias-precedence) in the

repro.py

from pydantic import BaseModel, Field


class Model(BaseModel):
    first_name: str = Field(
        alias="firstName",
        validation_alias="FIRST_NAME",
        serialization_alias="f_name",
        alias_priority=1
    )


model = Model(firstName="Pippo")   # ValidationError, no way to tweak alias_priority to be able to validate via plain_alias
print(model.model_dump())
print(model.model_dump(by_alias=True))   # Serialization via serialization_alias only

verify

Re-run the minimal reproduction on your broken version, then apply the fix and re-run.

fix.md

Option A — Upgrade to fixed release\npip install pydantic==1.10.17\nWhen NOT to use: This fix is not applicable if the documentation is already accurate regarding alias_priority usage.\n\n

Why This Fix Works in Production

Trigger: [docs]: cannot leverage on alias_priority if alias_generator is not involved
Mechanism: Documentation incorrectly suggested that alias_priority can be used without an AliasGenerator
Why the fix works: Updated documentation to clarify the use of alias_priority with alias_generator in Pydantic. (first fixed release: 1.10.17).

Production impact:

If left unfixed, the same config can fail only in production (env differences), causing startup failures or partial feature outages.

Why This Breaks in Prod

Documentation incorrectly suggested that alias_priority can be used without an AliasGenerator
Production symptom (often without a traceback): [docs]: cannot leverage on alias_priority if alias_generator is not involved

Proof / Evidence

GitHub issue: #9678
Fix PR: https://github.com/pydantic/pydantic/pull/9684
First fixed release: 1.10.17
Reproduced locally: No (not executed)
Last verified: 2026-02-09
Confidence: 0.85
Did this fix it?: Yes (upstream fix exists)
Own content ratio: 0.52

Discussion

High-signal excerpts from the issue thread (symptoms, repros, edge-cases).

Jump to Sources Open on GitHub

“@AlessandroMiola, Great catch. This is definitely wrong. I'll open a fix in a sec.”

@sydney-runkle · 2024-06-18 · source

Failure Signature (Search String)

[docs]: cannot leverage on alias_priority if alias_generator is not involved
I would like to point out a possible (I apologize if this is not the case and I'm missing something) inconsistency in the documentation at

Copy-friendly signature

signature.txt

Failure Signature
-----------------
[docs]: cannot leverage on alias_priority if alias_generator is not involved
I would like to point out a possible (I apologize if this is not the case and I'm missing something) inconsistency in the documentation at https://docs.pydantic.dev/latest/concepts/fields/#field-aliases, where the note specifies that

Error Message

Signature-only (no traceback captured)

error.txt

Error Message
-------------
[docs]: cannot leverage on alias_priority if alias_generator is not involved
I would like to point out a possible (I apologize if this is not the case and I'm missing something) inconsistency in the documentation at https://docs.pydantic.dev/latest/concepts/fields/#field-aliases, where the note specifies that

Minimal Reproduction

repro.py

from pydantic import BaseModel, Field


class Model(BaseModel):
    first_name: str = Field(
        alias="firstName",
        validation_alias="FIRST_NAME",
        serialization_alias="f_name",
        alias_priority=1
    )


model = Model(firstName="Pippo")   # ValidationError, no way to tweak alias_priority to be able to validate via plain_alias
print(model.model_dump())
print(model.model_dump(by_alias=True))   # Serialization via serialization_alias only

Environment

Pydantic: 2

What Broke

Users were misled about the functionality of alias_priority, causing confusion in implementation.

Why It Broke

Documentation incorrectly suggested that alias_priority can be used without an AliasGenerator

Fix Options (Details)

Option A — Upgrade to fixed release Safe default (recommended)

pip install pydantic==1.10.17

When NOT to use: This fix is not applicable if the documentation is already accurate regarding alias_priority usage.

Use when you can deploy the upstream fix. It is usually lower-risk than long-lived workarounds.

Fix reference: https://github.com/pydantic/pydantic/pull/9684

First fixed release: 1.10.17

Last verified: 2026-02-09. Validate in your environment.

When NOT to Use This Fix

This fix is not applicable if the documentation is already accurate regarding alias_priority usage.

Verify Fix

verify

Re-run the minimal reproduction on your broken version, then apply the fix and re-run.

Did This Fix Work in Your Case?

Quick signal helps us prioritize which fixes to verify and improve.

Prevention

Add a CI check that diffs key outputs after upgrades (OpenAPI schema snapshots, JSON payload shapes, CLI output).
Upgrade behind a canary and run integration tests against the canary before 100% rollout.

Version Compatibility Table

Version	Status
1.10.17	Fixed

Related Issues

No related fixes found.

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Related clusters: Data consistency OpenAPI schema Serialization

Sources

We don’t republish the full GitHub discussion text. Use the links above for context.

Pydantic [docs]: cannot leverage on alias_priority if alias_generator is not involved (Fix)