Falcon Middleware: SQLAlchemy Integration

The falcon-sqla package provides a middleware component for managing SQLAlchemy sessions. The manager component can also serve as a base building block or a recipe for more complex use cases, such as applications leveraging multiple database binds.

Installation

$ pip install falcon-sqla

Usage

The falcon_sqla session Manager can be used in two ways:

• As a Falcon middleware component.
• As a context manager to explicitly provide a database session.

Configuration

• Create a SQLAlchemy engine.
• Pass the engine to the Manager() initializer as its first parameter.
• If using the manager as a middleware component, pass its middleware property to a falcon.App's middleware list:

engine = create_engine('dialect+driver://my/database')
manager = falcon_sqla.Manager(engine)

app = falcon.App(middleware=[manager.middleware])

# The database session will be available as req.context.session

Context Manager

A falcon_sqla.Manager can also explicitly provide a database session using the session_scope() context manager:

# Somewhere inside a responder
with self.manager.session_scope(req, resp) as session:
    # Use the session
    # <...>

session_scope() can also be used as a standalone session context outside of the request-response cycle:

with self.manager.session_scope() as session:
    # Use the session
    # <...>

Custom Vertical Partitioning

Simple random selection of read- and write- database replicas is supported out of the box. Use the add_engine() method to instruct the Manager to include the provided engines in the runtime bind selection logic:

manager = falcon_sqla.Manager(engine)

read_replica = create_engine('dialect+driver://my/database.replica')
manager.add_engine(read_replica, falcon_sqla.EngineRole.READ)

The Manager.get_bind() method can be overridden to implement custom engine selection logic for more complex use cases.

See also this SQLAlchemy recipe: Custom Vertical Partitioning.

About Falcon

Falcon is the minimalist REST API and microservices framework for Python developers, with a focus on reliability, correctness, and performance at scale.

About SQLAlchemy

SQLAlchemy is the Python SQL toolkit and Object Relational Mapper that gives application developers the full power and flexibility of SQL.