SQLAlchemy基本使用

介紹

SQLAlchemy是一個基於Python實現的ORM框架。該框架創建在 DB API之上,使用關係對象映射進行數據庫操做,簡言之即是:將類和對象轉換成SQL,而後使用數據API執行SQL並獲取執行結果。python

做用

幫助咱們使用類和對象快速實現數據庫操做。mysql

安裝

pip3 install sqlalchemy

組成部分:

  • Engine,框架的引擎sql

  • Connection Pooling ,數據庫鏈接池數據庫

  • Dialect,選擇鏈接數據庫的DB API種類session

  • Schema/Types,架構和類型架構

  • SQL Exprression Language,SQL表達式語言框架

 示例

- 用戶登陸示例
- 用戶註冊示例
- 數據庫獲取數據實時更新(重寫構造方法)ui

使用

建立數據庫單表

#!/usr/bin/env python
# -*- coding:utf-8 -*-
import datetime
from sqlalchemy import create_engine
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import Column, Integer, String, Text, ForeignKey, DateTime, UniqueConstraint, Index

Base = declarative_base()


class Users(Base):
    __tablename__ = 'users'

    id = Column(Integer, primary_key=True)
    name = Column(String(32), index=True, nullable=False)
    # email = Column(String(32), unique=True)
    # ctime = Column(DateTime, default=datetime.datetime.now)
    # extra = Column(Text, nullable=True)

    __table_args__ = (
        # UniqueConstraint('id', 'name', name='uix_id_name'),
        # Index('ix_id_name', 'name', 'email'),
    )


def init_db():
    """
    根據類建立數據庫表
    :return: 
    """
    engine = create_engine(
        "mysql+pymysql://root:123@127.0.0.1:3306/s6?charset=utf8",    #用戶名:密碼@本機ip:數據庫端口3306/數據庫名?字符集
        max_overflow=0,  # 超過鏈接池大小外最多建立的鏈接
        pool_size=5,  # 鏈接池大小
        pool_timeout=30,  # 池中沒有線程最多等待的時間,不然報錯
        pool_recycle=-1  # 多久以後對線程池中的線程進行一次鏈接的回收(重置)
    )

    Base.metadata.create_all(engine)


def drop_db():
    """
    根據類刪除數據庫表
    :return: 
    """
    engine = create_engine(
        "mysql+pymysql://root:123@127.0.0.1:3306/s6?charset=utf8",
        max_overflow=0,  # 超過鏈接池大小外最多建立的鏈接
        pool_size=5,  # 鏈接池大小
        pool_timeout=30,  # 池中沒有線程最多等待的時間,不然報錯
        pool_recycle=-1  # 多久以後對線程池中的線程進行一次鏈接的回收(重置)
    )

    Base.metadata.drop_all(engine)


if __name__ == '__main__':
    drop_db()
    init_db() 

操做數據庫表

#!/usr/bin/env python
# -*- coding:utf-8 -*-
from sqlalchemy.orm import sessionmaker
from sqlalchemy import create_engine
from models import Users
  
engine = create_engine("mysql+pymysql://root:123456@127.0.0.1:3306/s6", max_overflow=0, pool_size=5)
Session = sessionmaker(bind=engine)
  
# 每次執行數據庫操做時,都須要建立一個session
session = Session()
  
# ############# 執行ORM操做 #############
obj1 = Users(name="alex1")
session.add(obj1)
  
# 提交事務
session.commit()
# 關閉session
session.close()   

基本增刪改查

#!/usr/bin/env python
# -*- coding:utf-8 -*-
import time
import threading

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

from db import Users, Hosts

engine = create_engine("mysql+pymysql://root:123456@127.0.0.1:3306/s6", max_overflow=0, pool_size=5)
Session = sessionmaker(bind=engine)

session = Session()

# ################ 添加 ################
"""
obj1 = Users(name="yaya")
session.add(obj1)

session.add_all([
    Users(name="yaya"),
    Users(name="xiaoqiang"),
    Hosts(name="c1.com"),
])
session.commit()
"""

# ################ 刪除 ################
"""
session.query(Users).filter(Users.id > 2).delete()
session.commit()
"""
# ################ 修改 ################
"""
session.query(Users).filter(Users.id > 0).update({"name" : "099"})
session.query(Users).filter(Users.id > 0).update({Users.name: Users.name + "099"}, synchronize_session=False)
session.query(Users).filter(Users.id > 0).update({"age": Users.age + 1}, synchronize_session="evaluate")
session.commit()
"""
# ################ 查詢 ################
"""
r1 = session.query(Users).all()
r2 = session.query(Users.name.label('xx'), Users.age).all()
r3 = session.query(Users).filter(Users.name == "yaya").all()
r4 = session.query(Users).filter_by(name='alex').all()
r5 = session.query(Users).filter_by(name='alex').first()
r6 = session.query(Users).filter(text("id<:value and name=:name")).params(value=224, name='fred').order_by(Users.id).all()
r7 = session.query(Users).from_statement(text("SELECT * FROM users where name=:name")).params(name='ed').all()
"""

session.close()

其餘經常使用操做  

# ############################## 其餘經常使用 ###############################
# 1. 指定列
 select id,name as cname from users;
 result = session.query(Users.id,Users.name.label('cname')).all()
 for item in result:
         print(item[0],item.id,item.cname)
# 2. 默認條件and
 session.query(Users).filter(Users.id > 1, Users.name == 'eric').all()
# 3. between
 session.query(Users).filter(Users.id.between(1, 3), Users.name == 'eric').all()
# 4. in
 session.query(Users).filter(Users.id.in_([1,3,4])).all()
 session.query(Users).filter(~Users.id.in_([1,3,4])).all()
# 5. 子查詢
 session.query(Users).filter(Users.id.in_(session.query(Users.id).filter(Users.name=='eric'))).all()
# 6. and 和 or
 from sqlalchemy import and_, or_
 session.query(Users).filter(Users.id > 3, Users.name == 'eric').all()
 session.query(Users).filter(and_(Users.id > 3, Users.name == 'eric')).all()
 session.query(Users).filter(or_(Users.id < 2, Users.name == 'eric')).all()
 session.query(Users).filter(
     or_(
         Users.id < 2,
         and_(Users.name == 'eric', Users.id > 3),
         Users.extra != ""
     )).all()

# 7. filter_by
 session.query(Users).filter_by(name='alex').all()

# 8. 通配符
 ret = session.query(Users).filter(Users.name.like('e%')).all()    #e% 以e開頭的全部,e_ 以e開頭的一個
 ret = session.query(Users).filter(~Users.name.like('e%')).all()   #~ 指 not in

# 9. 切片(限制)
 result = session.query(Users)[1:2]

# 10.排序
 ret = session.query(Users).order_by(Users.name.desc()).all()
 ret = session.query(Users).order_by(Users.name.desc(), Users.id.asc()).all()

# 11. group by    #根據聚合索引進行二次查詢要用having
from sqlalchemy.sql import func

 ret = session.query(
         Users.depart_id,
         func.count(Users.id),
 ).group_by(Users.depart_id).all()
 for item in ret:
         print(item)

 from sqlalchemy.sql import func

 ret = session.query(
         Users.depart_id,
         func.count(Users.id),
 ).group_by(Users.depart_id).having(func.count(Users.id) >= 2).all()
 for item in ret:
         print(item)

# 12.union 和 union all
"""
select id,name from users
UNION          
select id,name from users;
"""
 q1 = session.query(Users.name).filter(Users.id > 2)
 q2 = session.query(Favor.caption).filter(Favor.nid < 2)
 ret = q1.union(q2).all()   #union上下拼接去重

 q1 = session.query(Users.name).filter(Users.id > 2)
 q2 = session.query(Favor.caption).filter(Favor.nid < 2)
 ret = q1.union_all(q2).all()   #union_all 上下拼接不去重  ,join左右拼接
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