Day 27 - Databases

Author: Zemerik

Day 27 - Databases/README.md

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+# Day 27: Databases
+
+## What You'll Learn:
+- SQLite database connections
+- Executing SQL queries from Python
+- Using SQLAlchemy ORM
+- CRUD (Create, Read, Update, Delete) operations
+- Database transactions and error handling
+
+## Files:
+1. `sqlite_basics.py` - Raw SQL operations
+2. `crud_operations.py` - Basic CRUD functionality
+3. `orm_example.py` - SQLAlchemy ORM usage
+4. `database_schema.sql` - Table creation schema
+
+## Exercises:
+1. Create a contact manager that:
+   - Stores name/email/phone in SQLite
+   - Allows search by name/phone
+   - Exports contacts to CSV
+
+2. Build an inventory system with:
+   - Product table (name, price, quantity)
+   - Daily sales tracking table
+   - Low stock alerts

Day 27 - Databases/crud_operations.py

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+import sqlite3
+
+class UserManager:
+    def __init__(self, db_name='users.db'):
+        self.conn = sqlite3.connect(db_name)
+        self.cursor = self.conn.cursor()
+        self._create_table()
+
+    def _create_table(self):
+        self.cursor.execute('''CREATE TABLE IF NOT EXISTS users
+                            (id INTEGER PRIMARY KEY,
+                            name TEXT NOT NULL,
+                            age INTEGER)''')
+        self.conn.commit()
+
+    def add_user(self, name, age):
+        self.cursor.execute("INSERT INTO users (name, age) VALUES (?, ?)",
+                          (name, age))
+        self.conn.commit()
+
+    def get_users(self):
+        return self.cursor.execute("SELECT * FROM users").fetchall()
+
+    def __del__(self):
+        self.conn.close()
+
+# Usage
+manager = UserManager()
+manager.add_user("Bob", 30)
+print("All users:", manager.get_users())

Day 27 - Databases/database_schema.sql

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+-- Schema for blog application
+CREATE TABLE IF NOT EXISTS posts (
+    id INTEGER PRIMARY KEY,
+    title TEXT NOT NULL,
+    content TEXT,
+    created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
+);
+
+CREATE TABLE IF NOT EXISTS comments (
+    id INTEGER PRIMARY KEY,
+    post_id INTEGER,
+    author TEXT,
+    comment TEXT,
+    FOREIGN KEY(post_id) REFERENCES posts(id)
+);

Day 27 - Databases/orm_example.py

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+from sqlalchemy import create_engine, Column, Integer, String
+from sqlalchemy.ext.declarative import declarative_base
+from sqlalchemy.orm import sessionmaker
+
+Base = declarative_base()
+engine = create_engine('sqlite:///orm.db')
+
+class Product(Base):
+    __tablename__ = 'products'
+    id = Column(Integer, primary_key=True)
+    name = Column(String(50))
+    price = Column(Integer)
+    quantity = Column(Integer)
+
+Base.metadata.create_all(engine)
+
+Session = sessionmaker(bind=engine)
+session = Session()
+
+# Add product
+new_product = Product(name="Laptop", price=999, quantity=5)
+session.add(new_product)
+session.commit()
+
+# Query products
+print("All products:", session.query(Product).all())

Day 27 - Databases/requirements.txt

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+SQLAlchemy==2.0.20

Day 27 - Databases/sqlite_basics.py

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+import sqlite3
+
+# Create database connection
+conn = sqlite3.connect('mydatabase.db')
+cursor = conn.cursor()
+
+# Create table
+cursor.execute('''CREATE TABLE IF NOT EXISTS users
+               (id INTEGER PRIMARY KEY, 
+               name TEXT, 
+               email TEXT)''')
+
+# Insert data
+cursor.execute("INSERT INTO users (name, email) VALUES (?, ?)",
+              ('Alice', 'alice@example.com'))
+
+# Commit and close
+conn.commit()
+conn.close()