I've just started learning FastAPI and want to build practical applications rather than only follow short tutorials. What mistakes did you make early on that are worth avoiding? I'm especially interested in async code, database access, authentication, dependency injection, project structure, and deploying APIs. What learning path or resources helped you become comfortable using FastAPI in production-style projects?
4 Answers
A common mistake is mixing synchronous and asynchronous code without understanding the tradeoffs. Learn when to use async route handlers, especially for database operations and external API calls, instead of assuming every function should be async. Dependency injection is another feature worth learning early; it works well for authentication, shared settings, and database sessions, and can keep route handlers very small. The official documentation is a strong resource. After learning the basics, build something with a real database and a few asynchronous external calls rather than stopping at a simple tutorial app.
A useful project structure is to group the web routes, service logic, and data-access code separately, often with matching module names for each feature. For example, a feature can have an API module for endpoints, a service module for workflows, and a data module for persistence. Start with a small structure and add layers when the project needs them rather than creating a huge architecture up front. Dependency injection becomes especially valuable once those pieces need to share database sessions or configuration.
FastAPI is a good fit for serving model-backed APIs and AI integrations, so you don’t need to switch frameworks just because the application involves machine learning. The important part is to keep long-running inference, business rules, and integrations out of the route functions. Use background jobs or a separate worker when a model call is too slow for a normal request, and choose deployment components such as a reverse proxy and process manager based on the environment rather than treating them as part of the framework itself.
Try to keep FastAPI focused on API concerns: request validation, response serialization, OpenAPI documentation, routing, and dependencies. Put business rules and workflows in separate service or domain modules, with data-access code in its own layer. That way your route functions may only validate the request, call a service, and return the result. It also makes the application easier to test and less tightly coupled to the web framework.
That separation makes sense for the AI projects I want to build. I’ll keep the model and business logic in service modules while using FastAPI mainly for the API layer.
That’s really helpful, especially the advice to build something with a database and external calls instead of repeating tiny tutorial projects.