MySQL— pymysql and SQLAlchemy

目錄

1、pymysql

2、SQLAlchemy

1、pymysql

pymsql是Python中操做MySQL的模塊，其使用方法和MySQLdb幾乎相同。

1. 下載安裝

#在終端直接運行
pip3 install pymysql

2. 使用操做

a. 執行SQL

#!/usr/bin/env python
# -*- coding:utf-8 -*-
import pymysql
  
# 建立鏈接
conn = pymysql.connect(host='127.0.0.1', port=3306, user='root', passwd='123', db='t1')
# 建立遊標
cursor = conn.cursor()
  
# 執行SQL，並返回受影響行數
effect_row = cursor.execute("update hosts set host = '1.1.1.2'")
  
# 執行SQL，並返回受影響行數
#effect_row = cursor.execute("update hosts set host = '1.1.1.2' where nid > %s", (1,))
  
# 執行SQL，並返回受影響行數
#effect_row = cursor.executemany("insert into hosts(host,color_id)values(%s,%s)", [("1.1.1.11",1),("1.1.1.11",2)])
  
  
# 提交，否則沒法保存新建或者修改的數據
conn.commit()
  
# 關閉遊標
cursor.close()
# 關閉鏈接
conn.close()

b. 獲取新建立數據自增ID

#!/usr/bin/env python
# -*- coding:utf-8 -*-
import pymysql
  
conn = pymysql.connect(host='127.0.0.1', port=3306, user='root', passwd='123', db='t1')
cursor = conn.cursor()
cursor.executemany("insert into hosts(host,color_id)values(%s,%s)", [("1.1.1.11",1),("1.1.1.11",2)])
conn.commit()

# 獲取最新自增ID
new_id = cursor.lastrowid

cursor.close()
conn.close()

c. 獲取查詢數據

#!/usr/bin/env python
# -*- coding:utf-8 -*-
import pymysql
  
conn = pymysql.connect(host='127.0.0.1', port=3306, user='root', passwd='123', db='t1')
cursor = conn.cursor()
cursor.execute("select * from hosts")
  
# 獲取第一行數據
row_1 = cursor.fetchone()
  
# 獲取前n行數據
# row_2 = cursor.fetchmany(3)
# 獲取全部數據
# row_3 = cursor.fetchall()
  
conn.commit()
cursor.close()
conn.close()

注：在fetch數據時按照順序進行，可使用cursor.scroll(num,mode)來移動遊標位置，如：

• cursor.scroll(1,mode='relative')  　　 # 相對當前位置移動
• cursor.scroll(2,mode='absolute') 　　# 相對絕對位置移動

d. fetch數據類型

關於默認獲取的數據是元組類型，若是想要得到字典類型的數據，即：

#!/usr/bin/env python
# -*- coding:utf-8 -*-
import pymysql
  
conn = pymysql.connect(host='127.0.0.1', port=3306, user='root', passwd='123', db='t1')
  
# 遊標設置爲字典類型
cursor = conn.cursor(cursor=pymysql.cursors.DictCursor)
r = cursor.execute("call p1()")
  
result = cursor.fetchone()
  
conn.commit()
cursor.close()
conn.close()

2、SQLAlchemy

SQLAlchemy是Python編程語言下的一款ORM框架，該框架創建在數據庫API之上，使用關係對象映射進行數據庫操做，簡言之即是：將對象轉換成SQL，而後使用數據API執行SQL並獲取執行結果。

1. 下載安裝

#在終端直接運行
pip3 install SQLAlchemy

2. SQLAlchemy依賴關係

SQLAlchemy自己沒法操做數據庫，其必須依賴pymsql等第三方插件，Dialect用於和數據API進行交流，根據配置文件的不一樣調用不一樣的數據庫API，從而實現對數據庫的操做。

 

 

MySQL-Python
    mysql+mysqldb://<user>:<password>@<host>[:<port>]/<dbname>
   
pymysql
    mysql+pymysql://<username>:<password>@<host>/<dbname>[?<options>]
   
MySQL-Connector
    mysql+mysqlconnector://<user>:<password>@<host>[:<port>]/<dbname>
   
cx_Oracle
    oracle+cx_oracle://user:pass@host:port/dbname[?key=value&key=value...]

更多詳見：http://docs.sqlalchemy.org/en/latest/dialects/ index.html

3. ORM功能使用

使用 ORM/Schema Type/SQL Expression Language/Engine/ConnectionPooling/Dialect 全部組件對數據進行操做。根據類建立對象，對象轉換成SQL，執行SQL。

a. 建立表

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

#代表依賴關係並建立鏈接，最大鏈接數爲5 
engine = create_engine("mysql+pymysql://root:123@127.0.0.1:3306/t1", max_overflow=5)
 
Base = declarative_base()
 
# 建立單表
class Users(Base):
    __tablename__ = 'users'    # 表名
    id = Column(Integer, primary_key=True,autoincrement=True)    # id列，主鍵自增
    name = Column(String(32))    # name列
    extra = Column(String(16))    # extra列
 
    __table_args__ = (
    UniqueConstraint('id', 'name', name='uix_id_name'),    # 建立聯合惟一索引
        Index('ix_id_name', 'name', 'extra'),    # 建立普通索引
    )
 
 
# 一對多
class Favor(Base):
    __tablename__ = 'favor'
    nid = Column(Integer, primary_key=True)
    caption = Column(String(50), default='red', unique=True)
 
 
class Person(Base):
    __tablename__ = 'person'
    nid = Column(Integer, primary_key=True)
    name = Column(String(32), index=True, nullable=True)
    favor_id = Column(Integer, ForeignKey("favor.nid"))    # 建立外鍵
 
 
# 多對多
class Group(Base):
    __tablename__ = 'group'
    id = Column(Integer, primary_key=True)
    name = Column(String(64), unique=True, nullable=False)
    port = Column(Integer, default=22)
 
 
class Server(Base):
    __tablename__ = 'server'
    id = Column(Integer, primary_key=True, autoincrement=True)
    hostname = Column(String(64), unique=True, nullable=False)
 
 
class ServerToGroup(Base):
    __tablename__ = 'servertogroup'
    nid = Column(Integer, primary_key=True, autoincrement=True)
    server_id = Column(Integer, ForeignKey('server.id'))    # 建立外鍵
    group_id = Column(Integer, ForeignKey('group.id'))    # 建立外鍵
 
 
def init_db():
    Base.metadata.create_all(engine)
 
 
def drop_db():
    Base.metadata.drop_all(engine)

注：設置外鍵的另外一種方式 ForeignKeyConstraint(['other_id'], ['othertable.other_id'])

b. 操做表

 

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

engine = create_engine("mysql+pymysql://root:123@127.0.0.1:3306/t1", max_overflow=5)

Base = declarative_base()

# 建立單表
class Users(Base):
    __tablename__ = 'users'
    id = Column(Integer, primary_key=True)
    name = Column(String(32))
    extra = Column(String(16))

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

    def __repr__(self):
        return "%s-%s" %(self.id, self.name)

# 一對多
class Favor(Base):
    __tablename__ = 'favor'
    nid = Column(Integer, primary_key=True)
    caption = Column(String(50), default='red', unique=True)

    def __repr__(self):
        return "%s-%s" %(self.nid, self.caption)

class Person(Base):
    __tablename__ = 'person'
    nid = Column(Integer, primary_key=True)
    name = Column(String(32), index=True, nullable=True)
    favor_id = Column(Integer, ForeignKey("favor.nid"))
    # 與生成表結構無關，僅用於查詢方便
    favor = relationship("Favor", backref='pers')

# 多對多
class ServerToGroup(Base):
    __tablename__ = 'servertogroup'
    nid = Column(Integer, primary_key=True, autoincrement=True)
    server_id = Column(Integer, ForeignKey('server.id'))
    group_id = Column(Integer, ForeignKey('group.id'))
    group = relationship("Group", backref='s2g')
    server = relationship("Server", backref='s2g')

class Group(Base):
    __tablename__ = 'group'
    id = Column(Integer, primary_key=True)
    name = Column(String(64), unique=True, nullable=False)
    port = Column(Integer, default=22)
    # group = relationship('Group',secondary=ServerToGroup,backref='host_list')

class Server(Base):
    __tablename__ = 'server'

    id = Column(Integer, primary_key=True, autoincrement=True)
    hostname = Column(String(64), unique=True, nullable=False)

def init_db():
    Base.metadata.create_all(engine)

def drop_db():
    Base.metadata.drop_all(engine)

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

表結構 + 數據庫鏈接

b.1 增

#單條增長
obj = Users(name="alex0", extra='sb')
session.add(obj)

#多條增長
session.add_all([
    Users(name="alex1", extra='sb'),
    Users(name="alex2", extra='sb'),
])

#提交
session.commit()

 

b.2 刪

#先查詢到要刪除的記錄，再delete
session.query(Users).filter(Users.id > 2).delete()
session.commit()

 

b.3 改

#先查詢，再更新
session.query(Users).filter(Users.id > 2).update({"name" : "099"})    # 直接更改
session.query(Users).filter(Users.id > 2).update({Users.name: Users.name + "099"}, synchronize_session=False)    # 字符串拼接
session.query(Users).filter(Users.id > 2).update({"num": Users.num + 1}, synchronize_session="evaluate")    # 數字相加
session.commit()

 

b.4 查

 

ret = session.query(Users).all()
ret = session.query(Users.name, Users.extra).all()
ret = session.query(Users).filter_by(name='alex').all()
ret = session.query(Users).filter_by(name='alex').first()

ret = session.query(Users).filter(text("id<:value and name=:name")).params(value=224, name='fred').order_by(User.id).all()

ret = session.query(Users).from_statement(text("SELECT * FROM users where name=:name")).params(name='ed').all()

 

b.5 其它

 

#　條件
ret = session.query(Users).filter_by(name='alex').all()    # 條件內爲關鍵字表達式
ret = session.query(Users).filter(Users.id > 1, Users.name == 'eric').all()    # 條件內爲SQL表達式
ret = session.query(Users).filter(Users.id.between(1, 3), Users.name == 'eric').all()    # between
ret = session.query(Users).filter(Users.id.in_([1,3,4])).all()    # in
ret = session.query(Users).filter(~Users.id.in_([1,3,4])).all()    # not in
ret = session.query(Users).filter(Users.id.in_(session.query(Users.id).filter_by(name='eric'))).all()    # 子查詢條件

from sqlalchemy import and_, or_
ret = session.query(Users).filter(and_(Users.id > 3, Users.name == 'eric')).all()    # and
ret = session.query(Users).filter(or_(Users.id < 2, Users.name == 'eric')).all()    # or
ret = session.query(Users).filter(
    or_(
        Users.id < 2,
        and_(Users.name == 'eric', Users.id > 3),
        Users.extra != ""
    )).all()


# 通配符
ret = session.query(Users).filter(Users.name.like('e%')).all()    # e開頭
ret = session.query(Users).filter(~Users.name.like('e%')).all()    # 非e開頭

# 限制
ret = session.query(Users)[1:2]    # 至關於limit

# 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()

# 分組
from sqlalchemy.sql import func

ret = session.query(Users).group_by(Users.extra).all()
ret = session.query(
    func.max(Users.id),
    func.sum(Users.id),
    func.min(Users.id)).group_by(Users.name).all()

ret = session.query(
    func.max(Users.id),
    func.sum(Users.id),
    func.min(Users.id)).group_by(Users.name).having(func.min(Users.id) >2).all()

# 連表

ret = session.query(Users, Favor).filter(Users.id == Favor.nid).all()    # 笛卡兒積連表
ret = session.query(Person).join(Favor).all()    # 默認內連 inner join
ret = session.query(Person).join(Favor, isouter=True).all()    # 左連


# 組合
q1 = session.query(Users.name).filter(Users.id > 2)
q2 = session.query(Favor.caption).filter(Favor.nid < 2)
ret = q1.union(q2).all()

q1 = session.query(Users.name).filter(Users.id > 2)
q2 = session.query(Favor.caption).filter(Favor.nid < 2)
ret = q1.union_all(q2).all()

 

 

 

參考資料：

1. Python開發【第十九篇】：Python操做MySQL