👀 Views: 53 💬 Answers: 1 📅 Created: 2025-06-02

fastapi sqlalchemy database Python

I'm currently building a FastAPI application with SQLAlchemy for ORM, and I have a many-to-many relationship between `User` and `Group` models. When a user is added to a group, I need to ensure that they aren't added multiple times, but I'm struggling with how to handle this without resulting in a unique constraint behavior. When I try to add a user to a group that they are already a member of, I get the following behavior: `sqlalchemy.exc.IntegrityError: (sqlite3.IntegrityError) UNIQUE constraint failed: user_group.user_id`. Here's a simplified version of my models: ```python from sqlalchemy import Column, Integer, ForeignKey, Table from sqlalchemy.orm import relationship from sqlalchemy.ext.declarative import declarative_base Base = declarative_base() user_group = Table('user_group', Base.metadata, Column('user_id', Integer, ForeignKey('users.id'), primary_key=True), Column('group_id', Integer, ForeignKey('groups.id'), primary_key=True) ) class User(Base): __tablename__ = 'users' id = Column(Integer, primary_key=True) groups = relationship('Group', secondary=user_group, back_populates='users') class Group(Base): __tablename__ = 'groups' id = Column(Integer, primary_key=True) users = relationship('User', secondary=user_group, back_populates='groups') ``` When I attempt to execute this code to add a user to a group: ```python async def add_user_to_group(user_id: int, group_id: int): user = await session.get(User, user_id) group = await session.get(Group, group_id) user.groups.append(group) await session.commit() ``` I want to check if the user is already a member of the group before appending them, but I need to figure out the best way to query this without running into performance optimization. I tried adding this check: ```python if group not in user.groups: user.groups.append(group) await session.commit() ``` But it still results in the integrity behavior if there is a race condition where two requests try to add the same user to a group simultaneously. How can I safely handle this situation while ensuring that performance remains optimal? Any suggestions on how to avoid the duplicate entry behavior while maintaining a good user experience? I'm using FastAPI 0.68.0 and SQLAlchemy 1.4.22. Thanks for any insights!