SQLModel gets corrupted when used with Celery

[superboum]

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Example Code

from sqlmodel import SQLModel, Field
import time, signal, os

# === Setup ===

# https://docs.celeryq.dev/en/main/reference/celery.exceptions.html
class SoftTimeLimitExceeded(Exception):
    pass

# https://docs.python.org/3/library/signal.html#examples
def handler(signum, frame):
    raise SoftTimeLimitExceeded()

class Hero(SQLModel, table=True):
    id: int | None = Field(default=None, primary_key=True)
    name: str

    def __init__(self, **data):
        super().__init__(**data)
        time.sleep(2) # simulate a slow constructor

signal.signal(signal.SIGUSR1, handler)

# === Act ===
print(f"Reference Hero JSON: `Hero(name='foobar')` -> {Hero(name='foobar').model_dump_json()}")
print(f"Run in another terminal 'kill -SIGUSR1 {os.getpid()}' to corrupt SQLModel")
try:
    while True:
        Hero.model_validate({"name": "foobar"})
except SoftTimeLimitExceeded:
    print("Received SIGUSR1, interrupted. Hero is now corrupted.")


# === Observe ===
while True:
    print(f"Corrupted Hero JSON: `Hero(name='foobar')` -> {Hero(name='foobar').model_dump_json()}")

Description

Bug detection

This section is only for SEO, ie. help people in the same situation find this issue

We detected this issue in our codebase as we were starting to see that kind of PostgreSQL errors:

(psycopg.errors.NotNullViolation) null value in column "xxx" of relation "xxx" violates not-null constraint

Explanation

• model_validate is interrupted by an exception raised by a signal handler
  • It's how by default Celery handles soft task timeout
• exception is caught by the application, process continues its execution
• building an instance of SQLModel through its constructor now leads to an empty dict

Workaround

Note that one way to fix this error is to monkey patch partial_init:

import sqlmodel._compat as _sqlmodel_compat

@contextmanager
def _safe_partial_init() -> Generator[None, None, None]:
    token = _sqlmodel_compat.finish_init.set(False)
    try:
        yield
    finally:
        _sqlmodel_compat.finish_init.reset(token)


_sqlmodel_compat.partial_init = _safe_partial_init

However, it seems partial_init being interrupted by an exception is not the only codepath in SQLModel that can lead to corrupted models.

Operating System

Linux

Operating System Details

Reproduced in many environments (GKE cluster, local NixOS machine, macOS laptop, etc.), with different Python versions, on different SQLModel versions.

SQLModel Version

0.0.38

Python Version

3.13

Additional Context

Trace of a local execution of the reproducer:

Reference Hero JSON: `Hero(name='foobar')` -> {"name":"foobar","id":null}
Run in another terminal 'kill -SIGUSR1 27330' to corrupt SQLModel
Received SIGUSR1, interrupted. Hero is now corrupted.
Corrupted Hero JSON: `Hero(name='foobar')` -> {}
Corrupted Hero JSON: `Hero(name='foobar')` -> {}
Corrupted Hero JSON: `Hero(name='foobar')` -> {}