Python ORM vs. Raw SQL：性能权衡与选择时机

            
from sqlalchemy import create_engine, Column, Integer, String
from sqlalchemy.orm import sessionmaker
from sqlalchemy.ext.declarative import declarative_base

engine = create_engine('sqlite:///:memory:')
Base = declarative_base()

class User(Base):
    __tablename__ = 'users'
    id = Column(Integer, primary_key=True)
    name = Column(String)
    age = Column(Integer)

Base.metadata.create_all(engine)

Session = sessionmaker(bind=engine)
session = Session()

# Create some users
user1 = User(name='Alice', age=30)
user2 = User(name='Bob', age=25)
session.add_all([user1, user2])
session.commit()

# Query for a user by name
user = session.query(User).filter_by(name='Alice').first()
print(f"ORM: User found: {user.name}, {user.age}")

            

              
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import sqlite3

conn = sqlite3.connect(':memory:')
cursor = conn.cursor()

cursor.execute('''
    CREATE TABLE users (
        id INTEGER PRIMARY KEY,
        name TEXT,
        age INTEGER
    )
''')

# Insert some users
cursor.execute("INSERT INTO users (name, age) VALUES (?, ?)", ('Alice', 30))
cursor.execute("INSERT INTO users (name, age) VALUES (?, ?)", ('Bob', 25))
conn.commit()

# Query for a user by name
cursor.execute("SELECT name, age FROM users WHERE name = ?", ('Alice',))
user = cursor.fetchone()
print(f"Raw SQL: User found: {user[0]}, {user[1]}")
conn.close()

            

              
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from sqlalchemy import create_engine, Column, Integer, String, ForeignKey
from sqlalchemy.orm import sessionmaker, relationship
from sqlalchemy.ext.declarative import declarative_base

engine = create_engine('sqlite:///:memory:')
Base = declarative_base()

class User(Base):
    __tablename__ = 'users'
    id = Column(Integer, primary_key=True)
    name = Column(String)
    age = Column(Integer)
    orders = relationship("Order", back_populates="user")

class Order(Base):
    __tablename__ = 'orders'
    id = Column(Integer, primary_key=True)
    user_id = Column(Integer, ForeignKey('users.id'))
    product = Column(String)
    user = relationship("User", back_populates="orders")

Base.metadata.create_all(engine)

Session = sessionmaker(bind=engine)
session = Session()

# Create some users and orders
user1 = User(name='Alice', age=30)
user2 = User(name='Bob', age=25)
order1 = Order(user=user1, product='Laptop')
order2 = Order(user=user1, product='Mouse')
order3 = Order(user=user2, product='Keyboard')
session.add_all([user1, user2, order1, order2, order3])
session.commit()

# Query for users and their orders
users = session.query(User).all()
for user in users:
    print(f"ORM: User: {user.name}, Orders: {[order.product for order in user.orders]}")

#Demonstrates the N+1 problem.  Without eager loading, a query is executed for each user's orders.

            

              
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import sqlite3

conn = sqlite3.connect(':memory:')
cursor = conn.cursor()

cursor.execute('''
    CREATE TABLE users (
        id INTEGER PRIMARY KEY,
        name TEXT,
        age INTEGER
    )
''')

cursor.execute('''
    CREATE TABLE orders (
        id INTEGER PRIMARY KEY,
        user_id INTEGER,
        product TEXT,
        FOREIGN KEY (user_id) REFERENCES users(id)
    )
''')

# Insert some users and orders
cursor.execute("INSERT INTO users (name, age) VALUES (?, ?)", ('Alice', 30))
cursor.execute("INSERT INTO users (name, age) VALUES (?, ?)", ('Bob', 25))
user_id_alice = cursor.lastrowid # Get Alice's ID
cursor.execute("INSERT INTO orders (user_id, product) VALUES (?, ?)", (user_id_alice, 'Laptop'))
cursor.execute("INSERT INTO orders (user_id, product) VALUES (?, ?)", (user_id_alice, 'Mouse'))

user_id_bob = cursor.execute("SELECT id FROM users WHERE name = 'Bob'").fetchone()[0]
cursor.execute("INSERT INTO orders (user_id, product) VALUES (?, ?)", (user_id_bob, 'Keyboard'))

conn.commit()

# Query for users and their orders using JOIN
cursor.execute("""
    SELECT users.name, orders.product
    FROM users
    LEFT JOIN orders ON users.id = orders.user_id
"""")

results = cursor.fetchall()

user_orders = {}
for name, product in results:
    if name not in user_orders:
        user_orders[name] = []
    if product: #Product can be null
      user_orders[name].append(product)

for user, orders in user_orders.items():
    print(f"Raw SQL: User: {user}, Orders: {orders}")

conn.close()

            

              
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import timeit

# Setup code (create database, insert data, etc.) - same setup code from previous examples

# Function using ORM
def orm_query():
  #ORM query
  session = Session()
  user = session.query(User).filter_by(name='Alice').first()
  session.close()
  return user

# Function using Raw SQL
def raw_sql_query():
  #Raw SQL query
  conn = sqlite3.connect(':memory:')
  cursor = conn.cursor()
  cursor.execute("SELECT name, age FROM users WHERE name = ?", ('Alice',))
  user = cursor.fetchone()
  conn.close()
  return user


# Measure execution time for ORM
orm_time = timeit.timeit(orm_query, number=1000)

# Measure execution time for Raw SQL
raw_sql_time = timeit.timeit(raw_sql_query, number=1000)

print(f"ORM Execution Time: {orm_time}")
print(f"Raw SQL Execution Time: {raw_sql_time}")

            

              
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