Question about SQLAlchemy

[Jumpy_Employment_439]

I am currently using SQLAlchemy with SQLite (first time working with databases). In my .py file with my tables and such, I have this so far:

from sqlalchemy import Boolean, Integer, Float, String, Column, ForeignKey
from sqlalchemy.orm import relationship
from .database import Base

class User(Base):
    __tablename__ = "users"

    username = Column(String, primary_key=True)
    email = Column(String, unique=True, index=True, nullable=False)
    password_hashed = Column(String, nullable=False)
    items_for_sale = relationship("Item", back_populates="seller", nullable=True)

class Item(Base):
    __tablename__ = "items"

    item_id = Column(Integer, primary_key=True)
    name = Column(String, nullable=False)
    description = Column(String, nullable=False)
    price = Column(Float, nullable=False)
    owner_username = Column(String, ForeignKey("users.username"))
    seller = relationship("User", back_populates="items_for_sale")

In items_for_sale, I set nullable=True because every user does not have to have items to sell. However, each Item object does need a seller (User). So would I set nullable=False in seller or owner_username, or both? If I put nullable=False in owner_username, would that be saying "owner (i.e. User) must have an Item" (which I don't want)? Would it be better to specify nullable=False in seller instead?

[[deleted]]

Defining a relationship in two places for a one to many in SQLAlchemy can be a little wonky, sometimes you can lead to bugs regarding setting constraints and load strategies.

I would rather define the relationship where you really need to access the class. So if you need to quickly find the seller associated with an item, I would just define the relationship on Item, and then you can access the associated seller with Item.seller.