sqlalchemy——基本操作

以下所有代码片段都使用了统一的引用，该引用如下：

from sqlalchemy import create_engine, ForeignKey
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import Column, String, Integer, Table
from sqlalchemy.orm import relationship, sessionmaker

一、表结构设计

engine = create_engine("mysql+pymysql://root:root@localhost/study?charset=utf8", echo=True)  # 连接数据库,显示SQL语句

Base = declarative_base()  # 创建基类


class Student(Base):
    __tablename__ = 'students'  # 指定表名
    __table_args__ = {
        # "mysql_engine":"MyISAM",
        "mysql_charset":"utf8"
    }  
    # show create table students 可以查看建表语句;默认是Innodb,lating-1.如果想显示中文需要修改指定建表的类型,同时,engine也要指定编码格式
    id = Column(Integer, primary_key=True)  #指定主键
    name = Column(String(30))   #多个字段名
    gender = Column(Integer)
    std_id = Column(String(10))
    teacher = Column(String(30))

    def __str__(self):  #显示对象的时候打印名字
        return self.name


Base.metadata.create_all(engine)  # 创建所有继承自 Base 的类对应的表

sqlslchemy在数据库中创建表之前，会先检查该表是否存在，如果不存在，才会去创建新表。

class Student(Base):
    __tablename__ = 'students'  # 指定表名
    id = Column(Integer, primary_key=True)
    name = Column(String(30))
    gender = Column(Integer)
    std_id = Column(String(10))
    teacher = Column(String(30))
    **math = Column(Integer)**   #变量字段

    def __str__(self):
        return self.name

虽然新加了一个math 变量（字段），但是由于数据库中已有students表，所以不会去创建新表，match字段也就不存在。

二、基本增删改查

1.插入数据

Session = sessionmaker(bind=engine)  # 获取 Session类
ses = Session()  # 获取session对象

zhangsan = Student(name="zhangsan", gender=1, std_id='XS331', teacher='hanmeimei', math=90)
lisi = Student(name="lisi", gender=1, std_id='XS332', teacher='hanmeimei', math=10)
wangwu = Student(name="wangwu", gender=0, std_id='XS333', teacher='lilei', math=60)
zhaoliu = Student(name="zhaoliu", gender=0, std_id='XS337', teacher='lilei', math=80)
ses.add(zhangsan)  # 单条添加
ses.add_all([lisi, wangwu, zhaoliu])  # 批量添加
ses.commit()

2.修改数据

zhangsan = ses.query(Student).filter_by(name='zhangsan').first()  #先获取对象
zhangsan.math = 91  #更改对象的属性
ses.commit()   #提交

也可以在还创建数据的时候修改，就是在提交之前进行修改：

liqi = Student(name="liqi", gender=1, std_id='XS335', teacher='xiadonghai', math=100)   #实例化一个对象
ses.add(liqi)  #添加对象，也可以视作添加一条数据
liqi = ses.query(Student).filter_by(name='liqi').first()
liqi.gender = 0
ses.commit()

 在创建一个对象之后，未添加之前直接改变其属性。

liqi = Student(name="liqi", gender=1, std_id='XS335', teacher='xiadonghai', math=100)
liqi.gender = 0
ses.add(liqi)
ses.commit()

 除此之外还可以使用update。

sess.query(Student).filter_by(name='liming').update({'gender':0})
sess.commit()

3.删除

result = sess.query(Student).filter(Student.id == 1 ).delete()
sess.commit()
result = sess.query(Student).filter(Student.id == 2 ).first()
sess.delete(result)
sess.commit()

4.查询

查询操作在数据库操作中总是最复杂的，下面介绍一些常用的操作。

（1）算术操作符

= 操作符
students_99 = sess.query(Student).filter_by(name ='zhangsan').all()
students_100 = sess.query(Student).filter(Student.name == 'zhangsan').all()
for i in students_100:
   print(i.name)

！= 操作符
student_101 = sess.query(Student).filter_by(name != 'liming').all()  # error
student_98 = sess.query(Student).filter(Student.name != 'liming').all()
for i in student_98:
  print(i.name)

 > ,<, <=, >=, 操作符
student_60 = sess.query(Student).filter(Student.math > 10).all()
student_61= sess.query(Student).filter_by(math>10).all()  # error
student_62 = sess.query(Student).filter(Student.math < 100).all()
student_63 = sess.query(Student).filter(Student.math <= 90).all()
student_64 = sess.query(Student).filter(Student.math >= 90).all()
student_64 = sess.query(Student).filter(Student.math <> 90).all()  # error
for i in student_60:
    print(i.math)
for i in student_62:
    print(i.math)
for i in student_63:
    print(i.math)
for i in student_64:
    print(i.math)

（2）模糊查询

like 操作符  % 代表任意多个字符  _ 代表一个字符
student_17 = sess.query(Student).filter(Student.name.like("%i%")).all()
for i in student_17:
    print(i.name)
student_17_2 = sess.query(Student).filter(Student.name.like("%i_i")).all()
for i in student_17_2:
    print(i.name)

not like
student_70 = sess.query(Student).filter(~Student.name.like("%i_i")).all()
student_71 = sess.query(Student).filter(Student.name.notlike("%i_i")).all()
for i in student_70:
    print(i.name)
print(student_70 == student_71)

（3）区间选取

in 操作符
student_18 = sess.query(Student).filter(Student.name.in_(['zhangsan','lisi','wangwu'])).all()
for i in student_18:
    print(i.name)
not in
student_19 = sess.query(Student).filter(~Student.name.in_(['lisi'])).all()
student_19_2 = sess.query(Student).filter(Student.name.notin_(['lisi'])).all()
for i in student_19:
    print(i.name)
print(student_19 == student_19_2)

（4）分页

student_10 = sess.query(Student).limit(2).offset(1).all()  #从第几条开始选取几条
student_11 = sess.query(Student).offset(1).limit(2).all()
student_12 = sess.query(Student)[1:3]
for i in student_10:
    print(i.id)
for i in student_11:
    print(i.id)
for i in student_12:
    print(i.id)

（5）排序

order_by 排序
student_33 = sess.query(Student).filter(text("math >= 10")).order_by(~text("math")).all()  # 逆序
student_33_2 = sess.query(Student).filter(text("math >= 10")).order_by(text("math")).all()  # 顺序
student_33_2_1 = sess.query(Student).filter(text("math >= 10")).order_by(desc(text("math"))).all()  # 逆序
student_33_3 = sess.query(Student).order_by(desc(Student.math)).all()  # 逆序
student_33_4 = sess.query(Student).order_by(Student.math.desc()).all()  # 逆序
student_33_5 = sess.query(Student).order_by(~Student.math).all()  # 逆序
student_33_6 = sess.query(Student).order_by(Student.math).all()  # 顺序
print(student_31)
print(student_32)
print("___"* 30)
for i in student_33:
    print(i.math)
print("___"* 30)
for i in student_33_2:
    print(i.math)
for i in student_33_3:
    print(i.math)
for i in student_33_4:
    print(i.math)
for i in student_33_5:
    print(i.math)
for i in student_33_6:
    print(i.math)

（6）分组

group_by 分组
student_39 = sess.query(Student).group_by(Student.gender == 1).count()
print(student_39)

（7）having：分组之后条件过滤

having
student_39_1 = sess.query(Student).group_by(Student.gender == 1).having(Student.math>60).all()
for i in student_39_1:
    print(i)

（8）计数

count
student_38 = sess.query(Student).filter_by(gender=1).count()
student_38_2 = sess.query(func.count(Student.name),Student.name).group_by(Student.name).all()
student_38_3 = sess.query(func.count(Student.name),Student.gender).group_by(Student.gender).all()
print(student_38_2)
print(student_38_3)

（9）去重

distinct
student_40 = sess.query(distinct(Student.name)).all()
for i in student_40:
    print(i)

（10）空值

是否为null
student_20 = sess.query(Student).filter(Student.name != None).all()
student_21 = sess.query(Student).filter(~Student.name.is_(None)).all()
student_22 = sess.query(Student).filter(Student.name.isnot(None)).all()
student_21_3 = sess.query(Student).filter(Student.name.is_('zhangsan')).all()  # error
student_21_2 = sess.query(Student).filter(Student.name.is_(1)).all()
for i in student_20:
    print(i.name)
print(student_20 == student_21 == student_22)

student_23 = sess.query(Student).filter(Student.math.is_(90)).all()
student_24 = sess.query(Student).filter(Student.math == None).all()

（11）逻辑操作

and
student_25 = sess.query(Student).filter(Student.gender == 1, Student.math > 70).all()
student_26 = sess.query(Student).filter(and_(Student.gender == 1, Student.math > 70)).all()  # 别忘了引入该方法
student_27 = sess.query(Student).filter(Student.gender == 1).filter(Student.math > 70).all()
for i in student_25:
    print(i.name)
print(student_25 == student_26 == student_27)

or
student_28 = sess.query(Student).filter(or_(Student.gender == 1, Student.math > 80)).all()
for i in student_28:
    print(i.name)

（12）text：原生sql语句

text  原生sql条件语句
student_31 = sess.query(Student).filter(text("name='lisi'")).first()  # 注意值为字符串时的写法
student_32 = sess.query(Student).filter(text("id=1")).first()  # 注意值为 数字 的写法
student_31 = sess.query(Student).filter(text("id>1 and math>10")).all()
for i in student_31:
    print(i.name)

text 插入变量
student_34 =sess.query(Student).filter(text("gender=:sex and math>:score")).params(sex=1, score=1).all()
for i in student_34:
    print(i.name)

from_statement 原生sql语句
student_35 = sess.query(Student).from_statement(text("select * from students where id=:id")).params(id=1).one()
student_36 = sess.query(Student).from_statement("select * from students where math>:score").params(score=10).all()
student_36_1 = sess.query(Student).from_statement("select * from students where math>10").all()
print(student_35)
for i in student_36:
    print(i.name)
print(student_36 == student_36_1)

（13）使用别名

student_7 = sess.query(Student.name.label('std_name')).all()
print(student_7)
for i in student_7:
    print(i.std_name)
    print(i[0])  # 第二种取值方式
student_8 = sess.query(Student.name).all()
print(student_8)
for i in student_8:
    print(i.name)
    print(i[0])

（14）取值

根据主键获取对象
students_1 = sess.query(Student).get(1)
print(students_1

value指定要获取的字段 返回的是生成器
students_3  = sess.query(Student).value(Student.name)
print(students_3)

values 指定多个字段 返回的是生成器
students_3_2  = sess.query(Student).values(Student.id,Student.name)
print(students_3_2)
for i in students_3_2:
    print(i)


一次获取多个字段值
students_4 = sess.query(Student.name,Student.gender).all()
print(students_4)
for i in students_4:
    print(i)

后续添加的方式选择要得到的字段结果
students_5 = sess.query(Student.name).add_columns(Student.gender).all()
print(students_5)
student_6 = sess.query(Student).filter_by(name="王大麻子").one()
print(student_6)

错误用法
error_1 = sess.query(Student).filter_by(and_(Student.id == 1, Student.name == 'lisi')).first()
error_2 = sess.query(Student).filter_by(and_(id=1, name='lisi')).first()
error_3 = sess.query(Student).filter(and_(id=1, name='lisi')).first()

one 有且只有一个，否则报错
student_30 = sess.query(Student).filter(Student.id == 1).one()
print(student_30)
可以只有一个或者没有，不能为多个结果，否则报错
student_31 = sess.query(Student).filter(Student.id == 10).one_or_none()
print(student_31)

student_13 = sess.query(Student).filter_by(id=1).one_or_none()
student_14 = sess.query(Student).filter(Student.id == 1).one_or_none()
print(student_13)
print(student_14)

（15）chain链式调用

student_15 = sess.query(Student).filter_by(gender=1).filter(Student.math>80).all()
# student_15_2 = sess.query(Student).filter_by(gender=1).filter_by(math>80).all()  # error
student_16 = sess.query(Student).filter(Student.gender == 1).filter(Student.math>80).all()
for i in student_15:
    print(i.name)
for i in student_16:
    print(i.name)