👀 Views: 90 💬 Answers: 1 📅 Created: 2025-06-06

Flask SQLAlchemy Database Python

I'm working on a Flask application using Flask-SQLAlchemy 2.5.1. I have two models: `Author` and `Book`, where each `Author` can have multiple `Books`. My goal is to retrieve all authors who have written books published after a specific year. However, when I try to filter the authors based on the publication year of their books, the query returns an empty list, even though I know there are matching records in the database. Here are the models I defined: ```python class Author(db.Model): id = db.Column(db.Integer, primary_key=True) name = db.Column(db.String(100), nullable=False) books = db.relationship('Book', backref='author', lazy=True) class Book(db.Model): id = db.Column(db.Integer, primary_key=True) title = db.Column(db.String(200), nullable=False) published_year = db.Column(db.Integer, nullable=False) author_id = db.Column(db.Integer, db.ForeignKey('author.id'), nullable=False) ``` I attempted the following query: ```python result = Author.query.join(Author.books).filter(Book.published_year > 2020).all() ``` However, `result` is an empty list. I printed the SQL generated by SQLAlchemy and it looks correct, but it still doesn't return any data. I also verified that there are authors and books in the database with the appropriate relationships set up. I even tried using `outerjoin` to see if it returns any authors without books published after 2020, but that still produced an empty list. ```python result = Author.query.outerjoin(Author.books).filter(Book.published_year > 2020).all() ``` This query also returns an empty list. I’m not seeing any errors in the logs, and I've confirmed the data is there with a direct SQL query to the database. Is there a specific question with how I'm filtering the query or an scenario with relationships in SQLAlchemy that might cause this? Any insights would be greatly appreciated!