How do I define relationships in SQLAlchemy?

How do I define relationships in SQLAlchemy?

In SQLAlchemy, you can define relationships using the relationship() function. You typically use it in conjunction with the ForeignKey constraint.

Can you give me an example of a one-to-many relationship?

Sure! For a one-to-many relationship, you might have a User model and a Post model. A user can have many posts, so in the User class, you would define posts = relationship('Post', back_populates='user') and in the Post class, you would have user_id = Column(Integer, ForeignKey('user.id')).

What about many-to-many relationships?

For many-to-many relationships, you need an association table. For example, if you have Student and Course, you would create an enrollment table that links them, and then use relationship() to connect them.

How do I query these relationships?

You can query relationships using the session object. For example, session.query(User).filter(User.id == some_id).first().posts will give you all posts for a specific user.