1.SQLALchemy使用
pip install sqlalchemy；
- SQLAlchemy是Python編程語言下的一款開源軟件，是PythonSQL工具包和對象關系映射器，它為應用程序開發(fā)人員提供了SQL的全部功能和靈活性
2.什么是ORM
- ORM（Object Relational Mapper）就是把數(shù)據(jù)庫表的行與相應的對象建立關聯(lián)，互相轉換；
- 目前，最知名的Python ORM是SQLAlchemy和SQLobject；
3.數(shù)據(jù)庫操作
- 創(chuàng)建表使用create_all()方法，刪除表使用drop_all()方法，我們一起來看一下如何創(chuàng)建和刪除表
# 導入引擎模塊
from sqlalchemy import create_engine
# 導入基類模塊
from sqlalchemy.ext.declarative import declarative_base
# 導入字段類
from sqlalchemy import Column, Integer, String
# 導入會話模塊
from sqlalchemy.orm import sessionmaker# 實體類的基類
Base = declarative_base()# 實體類
class Teacher(Base):'''實體類的創(chuàng)建有兩個方面的用處：1：如果數(shù)據(jù)庫中沒有表，那么可以使用實體類創(chuàng)建2：如果數(shù)據(jù)庫中有表，實體類可以映射表的結構，對表的CRUD操作'''# 表名必須指定__tablename__ = 'teacher'id = Column(Integer, primary_key=True, autoincrement=True)name = Column(String(255))age = Column(Integer)# 打印實例的使用可以發(fā)現(xiàn)，數(shù)據(jù)也是保存在實體類實例的__dict__中def __repr__(self):# print(self.__dict__)return "id='%s', name='%s', age='%s" % (self.id, self.name, self.age)__str__ = __repr__# 創(chuàng)建連接引擎
host = 'localhost'
port = 3306
username = 'zengzeng'
password = '123456'
db = 'XKD_Python_Course'
connect_str = 'mysql+mysqldb://{}:{}@{}:{}/{}'.format(username, password, host, port,db)
engine = create_engine(connect_str, echo=True)# 創(chuàng)建表
Base.metadata.create_all(engine)# 刪除表
# Base.metadata.drop_all(engine)
我們現(xiàn)在命令工具中查看一下數(shù)據(jù)庫中有沒有我們想要的teacher表，上一篇文章中講過，先登錄mysql：mysql -uzengzeng -p123456，然后進入我們要使用的數(shù)據(jù)庫：use XKD_Python_Course，我們先通過：show tables;查看一下數(shù)據(jù)庫中的表，發(fā)現(xiàn)沒有teacher表
那現(xiàn)在就可以執(zhí)行代碼，創(chuàng)建數(shù)據(jù)庫了，創(chuàng)建好后我們可以在命令行查看一下：show tables;，發(fā)現(xiàn)teacher表已經存在了，創(chuàng)建表成功yes!
查看表
想要刪除剛剛創(chuàng)建的表，可以使用drop_all()方法，執(zhí)行代碼，再查看數(shù)據(jù)庫表，就可以看teacher表已經被刪除了
Base.metadata.drop_all(engine)
- 插入數(shù)據(jù)使用session.add_all()方法；
from sqlalchemy import create_engine
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import Column, Integer, String
from sqlalchemy.orm import sessionmakerBase = declarative_base()
class Teacher(Base):__tablename__ = 'teacher'id = Column(Integer, primary_key=True, autoincrement=True)name = Column(String(255))age = Column(Integer)def __repr__(self):# print(self.__dict__)return "id='%s', name='%s', age='%s" % (self.id, self.name, self.age)__str__ = __repr__host = 'localhost'
port = 3306
username = 'zengzeng'
password = '123456'
db = 'XKD_Python_Course'
connect_str = 'mysql+mysqldb://{}:{}@{}:{}/{}'.format(username, password, host, port,db)
engine = create_engine(connect_str, echo=True)# 創(chuàng)建會話，用于提交數(shù)據(jù)
Session = sessionmaker(bind=engine)
session = Session()# 創(chuàng)建多行行實例，給表添加數(shù)據(jù)
try:lst = []for i in range(10):teacher = Teacher()teacher.name = 'zengzeng' + str(i)teacher.age = 20 + ilst.append(teacher)print(teacher)# session.add(student) 可以添加一行記錄，也可以添加多行記錄# 注意：這里將行記錄實例添加到session，不會提交，需要手動提交session.add_all(lst)except Exception as e:print('~~~~~~~~~~~'*200)session.rollback()print(e)
finally:session.commit()
我們執(zhí)行代碼，然后去命令工具查看一下表是否插入數(shù)據(jù)：select * from teacher;
插入數(shù)據(jù)
- 查詢操作使用session.query()方法，迭代查詢；
from sqlalchemy import create_engine
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import Column, Integer, String
from sqlalchemy.orm import sessionmakerBase = declarative_base()
class Teacher(Base):__tablename__ = 'teacher'id = Column(Integer, primary_key=True, autoincrement=True)name = Column(String(255))age = Column(Integer)def __repr__(self):# print(self.__dict__)return "id='%s', name='%s', age='%s" % (self.id, self.name, self.age)__str__ = __repr__host = 'localhost'
port = 3306
username = 'zengzeng'
password = '123456'
db = 'XKD_Python_Course'
conn_str = 'mysql+mysqldb://{}:{}@{}:{}/{}'.format(username, password, host, port,db)
engine = create_engine(conn_str, echo=False)Session = sessionmaker(bind=engine)
session = Session()teacher_obj = session.query(Teacher)
for teacher in teacher_obj:print(teacher) # 返回結果：{'_sa_instance_state': <sqlalchemy.orm.state.InstanceState object at 0x1063125f8>, 'age': 20, 'name': 'nihao0', 'id': 1}
print('*'*300)# 直接返回實例對象
teacher = session.query(Teacher).get(4)
print(teacher) # 返回結果：{'_sa_instance_state': <sqlalchemy.orm.state.InstanceState object at 0x1075fd400>, 'age': 23, 'name': 'nihao3', 'id': 4}
print(teacher.id) # 返回 aobama
print(teacher.name)
print(teacher.age)
print('*'*300)# 返回的是可迭代對象
teacher_results = session.query(Teacher).filter(Teacher.id == 5)
for teacher in teacher_results: # 拿到student實例對象print(teacher)
from sqlalchemy import create_engine
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import Column, Integer, String
from sqlalchemy.orm import sessionmakerBase = declarative_base()class Teacher(Base):__tablename__ = 'teacher'id = Column(Integer, primary_key=True, autoincrement=True)name = Column(String(255))age = Column(Integer)def __repr__(self):# print(self.__dict__)return "id='%s', name='%s', age='%s" % (self.id, self.name, self.age)__str__ = __repr__# 創(chuàng)建連接引擎
host = 'localhost'
port = 3306
username = 'zengzeng'
password = '123456'
db = 'XKD_Python_Course'
conn_str = 'mysql+mysqldb://{}:{}@{}:{}/{}'.format(username, password, host, port,db)
engine = create_engine(conn_str, echo=False)# 創(chuàng)建會話，用于提交數(shù)據(jù)
Session = sessionmaker(bind=engine)
session = Session()teacher = session.query(Teacher).get(4)
teacher.name = 'Robby'
teacher.age = '99'
session.commit()
where條件查詢
from sqlalchemy import create_engine
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import Column, Integer, String, DATE, Enum, ForeignKey
import enum
from sqlalchemy.orm import sessionmaker
Base = declarative_base()
class My_Enum(enum.Enum):M = 'M'F = 'F'# 實體類
class Emploee(Base):'''+------------+---------------+------+-----+---------+-------+| Field | Type | Null | Key | Default | Extra |+------------+---------------+------+-----+---------+-------+| emp_no | int(11) | NO | PRI | NULL | || birth_date | date | NO | | NULL | || first_name | varchar(14) | NO | | NULL | || last_name | varchar(16) | NO | | NULL | || gender | enum('M','F') | NO | | NULL | || hire_date | date | NO | | NULL | |+------------+---------------+------+-----+---------+-------+'''__tablename__ = 'employees'emp_no = Column(Integer, primary_key=True, nullable=False)birth_date = Column(DATE, nullable=False)first_name = Column(String(14), nullable=False)last_name = Column(String(16),nullable=False)gender = Column(Enum(My_Enum), nullable=False)hire_date = Column(DATE, nullable=False)def __repr__(self):return "emp_no='%s', birth_date='%s', first_name='%s', last_name='%s', gender='%s', hire_date='%s'" % (self.emp_no, self.birth_date, self.first_name, self.last_name, self.gender, self.hire_date)__str__ = __repr__# 創(chuàng)建連接引擎
host = 'localhost'
port = 3306
username = 'zengzeng'
password = '123456'
db = 'XKD_Python_Course'
conn_str = 'mysql+mysqldb://{}:{}@{}:{}/{}'.format(username, password, host, port,db)
engine = create_engine(conn_str, echo=False)# 創(chuàng)建表
Base.metadata.create_all(engine)# 創(chuàng)建會話，用于提交數(shù)據(jù)
Session = sessionmaker(bind=engine)
session = Session()# # 簡單的where條件查詢過濾， 返回可迭代對象, AND 取與
emploees = session.query(Emploee).filter(Emploee.emp_no < 10010).filter(Emploee.gender == 'M')
emploees = session.query(Emploee).filter((Emploee.emp_no > 10010) & (Emploee.gender == 'F'))# OR 取并
emploees = session.query(Emploee).filter((Emploee.emp_no > 10010) | (Emploee.gender == 'F'))# NOT 取反
emploees = session.query(Emploee).filter(~(Emploee.emp_no > 10010))# in
emploees = session.query(Emploee).filter(Emploee.emp_no.in_([10010, 10011, 10012]))# not in
emploees = session.query(Emploee).filter(~Emploee.emp_no.in_([10010, 10011, 10012]))# like ，like可以忽略大小寫進行模式匹配
emploees = session.query(Emploee).filter(Emploee.last_name.like('B%'))for emploee in emploees:print(emploee)
order排序
例如：
emploees = session.query(Emploee).filter(Emploee.last_name.like('B%')).order_by(Emploee.emp_no.asc())
例如：
emploees=session.query(Emploee).filter(Emploee.last_name.like('B%')).order_by(Emploee.emp_no.desc())
聚合與分組
- list()：轉化為列表；
- count()：聚合count(*)查詢；
- all()： 轉化為列表；
- limit().one()：查詢首行；
emploees = session.query(Emploee)
print(list(emploees)) # 轉化為列表
print(emploees.count()) # 聚合count(*)查詢
print(emploees.all()) # 轉化為列表
print(emploees.limit(1).one()) # 查詢首行
- max()：返回最大值；
- min()：返回最小值；
- avg()：返回平均值；
emploees = session.query(func.max(Emploee.emp_no))
emploees = session.query(func.min(Emploee.emp_no))
emploees = session.query(func.avg(Emploee.emp_no))
emploees = session.query(func.count(Emploee.emp_no)).group_by(Emploee.gender)
print(emploees)
for emploee in emploees:print(emploee)
參考：https://www.9xkd.com/user/plan-view.html?id=2415909403
總結
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