十八、python中使用SQLAlchemy(三)
发布日期:2021-10-31 07:31:27
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分类:技术文章
本文共 5966 字,大约阅读时间需要 19 分钟。
测试
继续以前面建立的student表作为示例进行后面的操作。
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。
from sqlalchemy import create_engine, Column, Integer, Stringfrom sqlalchemy.ext.declarative import declarative_basefrom sqlalchemy.orm import sessionmakerengine = 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。
student2 = session.query(Student).filter(Student.name == 'Alice').delete()session.commit()session.close()
数据库结果确认
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
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
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()
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1姓名中带字母e的人3个分组分组方法为group_by()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1001 Alice 22 beijing1003 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。
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)输出结果默认排序输出1006 For 50 beijing1002 Bob 69 beijing1005 Ever 97 beijing反序输出1005 Ever 97 beijing1002 Bob 69 beijing1006 For 50 beijing
总结
基本步骤
- 创建引擎engine
engine = create_engine("mysql+pymysql://root:123456@localhost/test")
- 创建session
DBsession = sessionmaker(bind=engine)session = DBsession()
- 定义模型
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
#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())#existsprint(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
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
from sqlalchemy import funcsession.query(func.count(User.id))session.query(func.count(User.id)).\ group_by(User.name)from sqlalchemy import distinctsession.query(func.count(distinct(User.name)))
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第一次来,支持一个
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