SQLite Integration for Beginners

Version: v0.18.0

When to Use

• User has app with in-memory storage (lists/arrays)
• User asks "How do I save data permanently?"
• User wants data to persist after restart

Prerequisites

• Working Flask/Sinatra app
• Understanding routes and templates
• At least one feature using list storage

What is SQLite?

List/Array: Like whiteboard notes - disappears when server stops SQLite: Like notebook - saved to file (notes.db), persists forever

Perfect for beginners:

• No server setup
• Built into Python
• Easy SQL basics
• Upgrades to PostgreSQL later

Key Concepts

Database Structure

Table = Spreadsheet
Columns = Data types (id, name, email)
Rows = Data entries

SQL Commands

Implementation

Flask

import sqlite3

def get_db():
    conn = sqlite3.connect('notes.db')
    conn.row_factory = sqlite3.Row
    return conn

def init_db():
    conn = get_db()
    conn.execute('''
        CREATE TABLE IF NOT EXISTS notes (
            id INTEGER PRIMARY KEY AUTOINCREMENT,
            text TEXT NOT NULL,
            created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
        )
    ''')
    conn.commit()
    conn.close()

@app.route('/')
def home():
    conn = get_db()
    notes = conn.execute('SELECT * FROM notes').fetchall()
    conn.close()
    return render_template('index.html', notes=notes)

Sinatra

require 'sqlite3'
DB = SQLite3::Database.new 'notes.db'
DB.results_as_hash = true

DB.execute <<-SQL
  CREATE TABLE IF NOT EXISTS notes (
    id INTEGER PRIMARY KEY AUTOINCREMENT,
    text TEXT NOT NULL,
    created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
  )
SQL

get '/' do
  @notes = DB.execute('SELECT * FROM notes')
  erb :index
end

SQL Explanation

• CREATE TABLE IF NOT EXISTS: Safe to run multiple times
• PRIMARY KEY AUTOINCREMENT: Unique auto-incrementing ID
• NOT NULL: Value required
• DEFAULT CURRENT_TIMESTAMP: Auto-filled time
• ? placeholder: Prevents SQL injection

Common Questions

• Database location: notes.db in project folder
• View inside: DB Browser for SQLite
• Mistake? Delete notes.db, it recreates
• Ruby install: gem install sqlite3

Troubleshooting

End of Skill