Default values for fields not working as expected with SQLModel in PostgreSQL

[Yoosuph]

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Issue Content

I'm encountering an issue where default values for fields in my SQLModel class are not being applied when using PostgreSQL. Despite specifying default or default_factory for various fields, the database does not seem to handle these defaults, and errors occur during table creation or insertion.

from datetime import datetime
from sqlmodel import Field, SQLModel
from typing import Optional

class Posts(SQLModel, table=True):
id: Optional[int] = Field(default_factory=int, primary_key=True)
title: str
content: str
published: Optional[bool] = Field(default_factory=lambda: True)
created_at: Optional[datetime] = Field(default_factory=datetime.now)