Reusing Queries with SQLAlchemy

In FastAPI applications, it’s often necessary to execute the same database query multiple times. To avoid code duplication and improve performance, you can reuse SQLAlchemy queries. This can be achieved using various techniques, such as creating query objects, using ORM expressions, and leveraging SQLAlchemy’s caching mechanisms.

Creating Query Objects

A common approach is to create query objects that can be reused throughout your application:

Python

from sqlalchemy.orm import Query

def get_user_by_email(db: Session, email: str) -> Optional[User]:
    query = db.query(User).filter(User.email == email)
    return query.first()

Using ORM Expressions

SQLAlchemy’s ORM expressions provide a flexible way to construct queries dynamically:

Python

from sqlalchemy import and_, or_

def get_users_by_name_or_email(db: Session, name: str, email: str) -> List[User]:
    query = db.query(User).filter(or_(User.name == name, User.email == email))
    return query.all()

Caching Queries

For frequently executed queries, you can consider caching the query results to improve performance. SQLAlchemy’s query.cache method can be used for simple caching:

Python

from sqlalchemy.orm import query

@query.cached(timeout=3600)
def get_popular_posts(db: Session) -> List[Post]:
    query = db.query(Post).order_by(Post.likes.desc()).limit(10)
    return query.all()

Additional Factors

• Query Optimization: Use SQLAlchemy’s query optimization techniques to improve performance, such as using joins and indexes.
• Data Validation: Validate user input to prevent SQL injection attacks and other security vulnerabilities.
• Error Handling: Implement appropriate error handling to catch database-related exceptions.