First install SQLAlchemy and use SQLite to create a database connection; 2. Define the User model and map it to the database table; 3. Initialize the engine and session, and create a data table; 4. Perform the addition, deletion, modification and search operations: add users, query condition data, update fields, and delete records; 5. After each operation, commit() must be called to submit the transaction, and finally close the session to free up resources.
Below is a practical Python SQLAlchemy example covering the complete process from installation, defining models, creating databases to adding, deleting, retrieving, and retrieving (CRUD) operations. Suitable for beginners to get started quickly.
? 1. Install SQLAlchemy
pip install sqlalchemy
? 2. Create database connections and models
We use SQLite as the sample database (no additional services required).
from sqlalchemy import create_engine, Column, Integer, String
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import sessionmaker
# Create base class Base = declarative_base()
# Define User model class User(Base):
__tablename__ = 'users'
id = Column(Integer, primary_key=True)
name = Column(String(50), nullable=False)
age = Column(Integer)
email = Column(String(100), unique=True)
def __repr__(self):
return f"<User(name='{self.name}', age={self.age}, email='{self.email}')>"? 3. Initialize database and session
# Create a database file (sqlite:///users.db) engine = create_engine('sqlite:///users.db', echo=True) # echo=True You can view SQL statements # Create a table (if it does not exist) Base.metadata.create_all(engine) # Create session Session = sessionmaker(bind=engine) session = Session()
echo=Truewill print out the executed SQL, which is convenient for debugging.
? 4. Add, delete, modify and check (CRUD) operation
? Insert data (Create)
# Add a single user new_user = User(name="Alice", age=30, email="alice@example.com")
session.add(new_user)
session.commit()
# Add users in batches = [
User(name="Bob", age=25, email="bob@example.com"),
User(name="Charlie", age=35, email="charlie@example.com")
]
session.add_all(users)
session.commit()? Query data (Read)
# Query all users all_users = session.query(User).all()
for user in all_users:
print(user)
# Conditional query: Find user with name Alice alice = session.query(User).filter_by(name="Alice").first()
print(alice)
# Use filter (support more complex conditions)
adults = session.query(User).filter(User.age > 25).all()
for user in adults:
print(user)? Update data (Update)
# Update Alice's age alice = session.query(User).filter_by(name="Alice").first()
If alice:
alice.age = 31
session.commit()Or more concise:
session.query(User).filter_by(name="Alice").update({"age": 31})
session.commit()? Delete data (Delete)
# Delete user session.query(User).filter_by(name="Charlie").delete() with name Charlie session.commit()
? 5. Close the session
session.close()
? Complete sample code (integrated version)
from sqlalchemy import create_engine, Column, Integer, String
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import sessionmaker
Base = declarative_base()
class User(Base):
__tablename__ = 'users'
id = Column(Integer, primary_key=True)
name = Column(String(50), nullable=False)
age = Column(Integer)
email = Column(String(100), unique=True)
def __repr__(self):
return f"<User(name='{self.name}', age={self.age}, email='{self.email}')>"
# Initialize the database engine = create_engine('sqlite:///users.db', echo=True)
Base.metadata.create_all(engine)
Session = sessionmaker(bind=engine)
session = Session()
# CRUD Example if __name__ == "__main__":
# Add if session.query(User).count() == 0: # Avoid repeated insertion of session.add_all([
User(name="Alice", age=30, email="alice@example.com"),
User(name="Bob", age=25, email="bob@example.com"),
])
session.commit()
# Query for user in session.query(User).all():
print(user)
# Update session.query(User).filter_by(name="Alice").update({"age": 31})
session.commit()
# Delete session.query(User).filter_by(name="Bob").delete()
session.commit()
session.close()? Summary
- SQLAlchemy provides clear ORM mapping to enable Python classes to correspond to database tables.
- Use
sessionto manage transactions,commit()to save changes. - Suitable for rapid development of small projects and supports complex queries for large applications.
Basically all this is not complicated but it is easy to ignore commit and session management.
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