python中使用SQLAlchemy（二）
由于目前工作比较忙，就借鉴其他大神的学习笔记，即使没有听课，但是也是看得懂下面的内容
关于SQLAlchemy使用建表、插入和查询内容，点击python中使用SQLAlchemy查看。
继续以前面建立的student表作为示例进行后面的操作。
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mysql> desc student; +---------+--------------+------+-----+---------+----------------+ | Field | Type | Null | Key | Default | Extra | +---------+--------------+------+-----+---------+----------------+ | id | int(11) | NO | PRI | NULL | auto_increment | | name | varchar(100) | YES | | NULL | | | age | int(11) | YES | | NULL | | | address | varchar(100) | YES | | NULL | | +---------+--------------+------+-----+---------+----------------+ 4 rows in set (0.15 sec) mysql> select * from student; +------+-------+------+---------+ | id | name | age | address | +------+-------+------+---------+ | 1001 | Alice | 25 | anhui | | 1002 | Bob | 69 | beijing | | 1003 | Cerry | 14 | jiangsu | +------+-------+------+---------+ 3 rows in set (0.07 sec) |
更新
更新时，首先查询需要更新的数据，然后直接更新对应字段即可。
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from sqlalchemy import create_engine, Column, Integer, String from sqlalchemy.ext.declarative import declarative_base from sqlalchemy.orm import sessionmaker engine = create_engine("mysql+pymysql://root:123456@localhost/test") DBsession = sessionmaker(bind=engine) session = DBsession() Base = declarative_base() class Student(Base): __tablename__ = 'student' id = Column(Integer, primary_key=True) name = Column(String(100)) age = Column(Integer) address = Column(String(100)) student1 = session.query(Student).filter(Student.name == 'Alice').one() print("更新前age：{0}".format(student1.age)) student1.age = '38' session.commit() print("更新后age：{0}".format(student1.age)) session.close() |
输出结果
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更新前age：25 更新后age：38 |
删除
删除时，首先查询出需要删除的数据，然后直接调用delete()方法直接删除即可。
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student2 = session.query(Student).filter(Student.name == 'Alice').delete() session.commit() session.close() |
数据库结果确认
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mysql> select * from student; +------+-------+------+---------+ | id | name | age | address | +------+-------+------+---------+ | 1002 | Bob | 69 | beijing | | 1003 | Cerry | 14 | jiangsu | +------+-------+------+---------+ 2 rows in set (0.00 sec) |
在进行分组及排序操作前，先插入几条数据
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student1 = Student(id=1001, name='Alice', age=22, address='beijing') student2 = Student(id=1004, name='Dany', age=14, address='beijing') student3 = Student(id=1005, name='Ever', age=97, address='beijing') student4 = Student(id=1006, name='For', age=50, address='beijing') session.add_all([student1, student2, student3, student4]) session.commit() session.close() |
数据库结果确认
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mysql> select * from student; +------+-------+------+---------+ | id | name | age | address | +------+-------+------+---------+ | 1001 | Alice | 22 | beijing | | 1002 | Bob | 69 | beijing | | 1003 | Cerry | 14 | jiangsu | | 1004 | Dany | 14 | beijing | | 1005 | Ever | 97 | beijing | | 1006 | For | 50 | beijing | +------+-------+------+---------+ 6 rows in set (0.00 sec) |
统计
统计方法为count()
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count_student = session.query(Student).filter(Student.name.like('%e%')).count() print("姓名中带字母e的人{0}个".format(count_student)) |
输出结果
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姓名中带字母e的人3个
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分组
分组方法为group_by()
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group_student = session.query(Student).group_by(Student.address).all() for i in group_student: print(i.id, i.name, i.age, i.address) |
输出结果
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1001 Alice 22 beijing 1003 Cerry 14 jiangsu |
排序
排序方法为order_by()，默认为升序，反序在order_by里面使用desc()方法。
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order_student = session.query(Student).filter(Student.age > 30).order_by(Student.age).all() print("默认排序输出") for x in order_student: print(x.id, x.name, x.age, x.address) orderdesc_student = session.query(Student).filter(Student.age > 30).order_by(Student.age.desc()).all() print("反序输出") for y in orderdesc_student: print(y.id, y.name, y.age, y.address) |
输出结果
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默认排序输出 1006 For 50 beijing 1002 Bob 69 beijing 1005 Ever 97 beijing 反序输出 1005 Ever 97 beijing 1002 Bob 69 beijing 1006 For 50 beijing |
总结
基本步骤
创建引擎engine
1engine = create_engine("mysql+pymysql://root:123456@localhost/test")创建session
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DBsession = sessionmaker(bind=engine) session = DBsession()
定义模型
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Base = declarative_base() class Student(Base): #Student类继承自Base类， __tablename__ = 'student' #对应数据库表名 id = Column(Integer, primary_key=True) #对应数据库各字段 name = Column(String(100)) age = Column(Integer) address = Column(String(100))
接下来基于前面创建的session和Student类及属性进行增删改查的操作。
常见查询总结
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#简单查询 print(session.query(Student).all()) print(session.query(Student.id, Student.name).all()) print(session.query(Student, Student.name).all()) #带条件查询 print(session.query(Student).filter_by(name='Bob').all()) print(session.query(Student).filter(Student.name == 'Bob').all()) print(session.query(Student).filter(Student.name.like('%e%')).all()) #多条件查询 from sqlalchemy import and_, or_ print(session.query(Student).filter(and_(Student.age > 20, Student.name.like('%e%'))).all()) print(session.query(Student).filter(or_(Student.age > 20, Student.name.like('%e%'))).all()) #sql过滤 print(session.query(Student).filter("id=:id").params(id=1001).all()) #关联查询 print(session.query(User, Address).filter(User.id == Address.user_id).all()) print(session.query(User).join(User.addresses).all()) print(session.query(User).outerjoin(User.addresses).all()) #聚合查询 print(session.query(User.name, func.count('*').label("user_count")).group_by(User.name).all()) print(session.query(User.name, func.sum(User.id).label("user_id_sum")).group_by(User.name).all()) #子查询 stmt = session.query(Address.user_id, func.count('*').label("address_count")).group_by(Address.user_id).subquery() print(session.query(User, stmt.c.address_count).outerjoin((stmt, User.id == stmt.c.user_id)).order_by(User.id).all()) #exists print(session.query(User).filter(exists().where(Address.user_id == User.id))) print(session.query(User).filter(User.addresses.any())) |
限制返回字段查询
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person = session.query(Person.name, Person.created_at, Person.updated_at).filter_by(name="zhongwei").order_by( Person.created_at).first() |
记录总数查询
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from sqlalchemy import func session.query(func.count(User.id)) session.query(func.count(User.id)).\ group_by(User.name) from sqlalchemy import distinct session.query(func.count(distinct(User.name))) |