How to define an Optional[Decimal] Field that yields to a constrained JSON schema

[joachimhuet]

First Check

• I added a very descriptive title here.
• I used the GitHub search to find a similar question and didn't find it.
• I searched the SQLModel documentation, with the integrated search.
• I already searched in Google "How to X in SQLModel" and didn't find any information.
• I already read and followed all the tutorial in the docs and didn't find an answer.
• I already checked if it is not related to SQLModel but to Pydantic.
• I already checked if it is not related to SQLModel but to SQLAlchemy.

Commit to Help

• I commit to help with one of those options 👆

Example Code

from typing import Optional
from decimal import Decimal
from sqlmodel import SQLModel, Field
from sqlalchemy import Column, DECIMAL

class ItemBase(SQLModel):
  ...
  price: Optional[Decimal] = Field(
    default=None, ge=0, le=100, sa_column=Column(DECIMAL(7,4)),
    regex=r"^\d+(\.\d+)?$"  # added for the string part to only accept numbers
  )

ItemBase.model_json_schema()
"""
{'properties': {'price': {'anyOf': [{'type': 'number'},
    {'type': 'string'},
    {'type': 'null'}],
   'default': None,
   'title': 'Price'}},
 'title': 'ItemBase',
 'type': 'object'}
"""

Description

The Optional makes minimum and maximum constraints disappear from number in model_json_schema.

This problem also occurs on Pydantic, but there we can use Annotated as a solution by making the type:
price: Optional[Annotated[Decimal, Field(max_digits=7, decimal_places=4, ge=0, le=100)]] = None

In sqlmodel however this yields to the error TypeError: issubclass() arg 1 must be a class

It is also frustrating to see the {type: string} in the json model for a decimal because it should be constrained with a regex or something to avoid passing pure text. But that is yet another problem and should be discussed in a pydantic thread instead.

Operating System

Linux, Windows

Operating System Details

No response

SQLModel Version

0.0.16

Python Version

3.9.13

Additional Context

I also created a stackoverflow question still waiting for an answer.

[joachimhuet]

Look at the answer in stackoverflow.