FastAPI ORM Explained

 

ORM in FastAPI/Uvicorn

What is ORM?

ORM stands for Object Relational Mapper. It allows you to work with databases using Python objects instead of writing raw SQL queries.

Instead of writing:

SELECT * FROM users WHERE id = 1;

You can write:

user = session.get(User, 1)

Here, User is a Python class mapped to a database table.

Common ORMs Used with FastAPI

1. SQLAlchemy

SQLAlchemy is the most commonly used ORM with FastAPI.

from sqlalchemy import Column, Integer, String
from database import Base

class User(Base):
    __tablename__ = "users"

    id = Column(Integer, primary_key=True)
    name = Column(String)

2. SQLModel

SQLModel combines Pydantic and SQLAlchemy and is beginner-friendly.

from sqlmodel import SQLModel, Field

class User(SQLModel, table=True):
    id: int | None = Field(default=None, primary_key=True)
    name: str

What is Uvicorn?

Uvicorn is an ASGI server used to run FastAPI applications.

Example:

uvicorn main:app --reload

• main → Python file name (main.py)
• app → FastAPI instance
• --reload → Auto reload during development

How They Work Together

Client Request
      ↓
Uvicorn (server)
      ↓
FastAPI (API framework)
      ↓
ORM (SQLAlchemy / SQLModel)
      ↓
Database (PostgreSQL/MySQL/SQLite)

Minimal FastAPI + ORM Example

from fastapi import FastAPI
from sqlmodel import SQLModel, Field

app = FastAPI()

class User(SQLModel, table=True):
    id: int | None = Field(default=None, primary_key=True)
    name: str

@app.get("/")
def read_root():
    return {"hello": "world"}

Run the application using:

uvicorn main:app --reload

Quick Summary

Term	Description
FastAPI	API framework
Uvicorn	Server that runs FastAPI
ORM	Database abstraction layer
SQLAlchemy	Popular ORM
SQLModel	FastAPI-friendly ORM