Intro to SQLModel (or SQLAlchemy)¶

🎯 What You’ll Learn¶

What SQLModel is and why it’s a great fit for FastAPI
How SQLModel compares to SQLAlchemy and Pydantic
How to define your first database model
How to prepare for database integration in your FastAPI app

🧠 What Is SQLModel?¶

SQLModel is a modern ORM (Object-Relational Mapper) built by the creator of FastAPI. It combines the best of:

SQLAlchemy: for powerful database access and schema generation
Pydantic: for data validation and serialization

This makes SQLModel ideal for FastAPI because:

You define your data models once and use them for both database and API validation
It supports both ORM mode (for database interaction) and Pydantic mode (for request/response validation)
It’s fully type-safe and integrates seamlessly with FastAPI

🔍 SQLModel vs SQLAlchemy vs Pydantic¶

Feature	SQLAlchemy	Pydantic	SQLModel (✅)
Database ORM	✅ Yes	❌ No	✅ Yes (via SQLAlchemy)
Data validation	❌ No	✅ Yes	✅ Yes (via Pydantic)
Type hints	⚠️ Partial	✅ Yes	✅ Yes
FastAPI integration	⚠️ Manual	✅ Yes	✅ Seamless
One model for all layers	❌ No	❌ No	✅ Yes

📦 Installing SQLModel and SQLite¶

We’ll use SQLite for simplicity — it’s file-based and requires no setup.

pip install sqlmodel

🧱 Step-by-Step: Define a SQLModel Task¶

Let’s define a Task model that maps to a database table.

📄 models/task.py

from sqlmodel import SQLModel, Field
from typing import Optional

class Task(SQLModel, table=True):
    id: Optional[int] = Field(default=None, primary_key=True)
    title: str
    description: Optional[str] = None
    completed: bool = False

🔍 Key Concepts¶

SQLModel is the base class (inherits from both Pydantic and SQLAlchemy)
table=True tells SQLModel to create a table for this model
Field(..., primary_key=True) marks id as the primary key
Optional[int] with default=None allows auto-incrementing IDs

🧰 What’s Next?¶

In the next lesson, you’ll:

Set up a SQLite database
Create the tables from your models
Use SQLModel’s session system to perform CRUD operations

🧠 Practice Challenge¶

Before moving on, try this:

Add a created_at: datetime field to the Task model
Set it to default to the current time using Field(default_factory=datetime.utcnow)

Let me know when you’re ready to move on to Creating models and tables with SQLModel, or if you want to explore SQLModel’s hybrid nature in more depth first.