Flask 第六话之数据库 -- SQLalchemy

一、sqlalchemy原生语句操作

from sqlalchemy import create_engine

HOSTNAME = '127.0.0.1'
PORT = 3306
DATABASE = 'demo'
USERNAME = 'root'
PASSWORD = '123456'

# 链接数据库的字符串，固定格式
DB_URL = "mysql+pymysql://{username}:{password}@{host}:{port}/{db}?charset=utf8".format(
    username = USERNAME,
    password = PASSWORD,
    host = HOSTNAME,
    port = PORT,
    db = DATABASE,
)

engine = create_engine(DB_URL)
# 判断是否链接成功
conn = engine.connect()

result = conn.execute('SELECT * FROM shop_area')

print(result.fetchone())

 二、定义一个简单的ORM模型

第一步：用declarative_base根据engine创建一个ORM基类

from sqlalchemy import create_engine
from sqlalchemy.ext.declarative import declarative_base
HOSTNAME = '127.0.0.1'
PORT = 3306
DATABASE = 'demo'
USERNAME = 'root'
PASSWORD = '123456'
# 链接数据库的字符串，固定格式
DB_URL = "mysql+pymysql://{username}:{password}@{host}:{port}/{db}?charset=utf8".format(
    username = USERNAME,
    password = PASSWORD,
    host = HOSTNAME,
    port = PORT,
    db = DATABASE,
)
engine = create_engine(DB_URL)
Base = declarative_base(engine)

第二步：用Base作为基类来定义自己的ORM类，首先定义__tablename__ = 'person'指定数据库表名。

class Person(Base):
    __tablename__ = 'person' # 表名

第三步：创建数据库映射的字段

from sqlalchemy import create_engine,Column,Integer,String
class Person(Base):
    __tablename__ = 'person' # 表名
    # 第二步：定义字段对象
    id = Column(Integer,primary_key=True,autoincrement=True)
    name = Column(String(50))
    age = Column(Integer)

第四步：将自己定义的ORM类映射到数据库中

Base.metadata.create_all()

 三、常用数据类型

1. Integer：整型，映射到数据库中是int类型。

2. Float：浮点类型，映射到数据库中是float类型。它占据的32位。

3. Double：双精度浮点类型，映射到数据库中是double类型，占据64位。

4. String：可变字符类型，映射到数据库中是varchar类型。

5. Boolean：布尔类型，映射到数据库中的是tinyint类型。

6. DECIMAL：定点类型。是专门为了解决浮点类型精度丢失的问题的。在存储钱相关的字段的时候建议大家都使用这个数据类型。并且这个类型使用的时候需要传递两个参数，第一个参数是用来标记这个字段总能能存储多少个数字，第二个参数表示小数点后有多少位。

7. Enum：枚举类型。指定某个字段只能是枚举中指定的几个值，不能为其他值。在ORM模型中，使用Enum来作为枚举。

8. Date：存储时间，只能存储年月日。映射到数据库中是date类型。在Python代码中，可以使用`datetime.date`来指定。

9. DateTime：存储时间，可以存储年月日时分秒毫秒等。映射到数据库中也是datetime类型。在Python代码中，可以使用`datetime.datetime`来指定。

10. Time：存储时间，可以存储时分秒。映射到数据库中也是time类型。在Python代码中，可以使用`datetime.time`来指定。

11. Text：存储长字符串。一般可以存储6W多个字符。如果超出了这个范围，可以使用LONGTEXT类型。映射到数据库中就是text类型。

12. LONGTEXT：长文本类型，映射到数据库中是longtext类型。

from sqlalchemy import create_engine
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import sessionmaker

HOSTNAME = '127.0.0.1'
PORT = 3306
DATABASE = 'demo'
USERNAME = 'root'
PASSWORD = '123456'

# 链接数据库的字符串，固定格式
DB_URL = "mysql+pymysql://{username}:{password}@{host}:{port}/{db}?charset=utf8".format(
    username = USERNAME,
    password = PASSWORD,
    host = HOSTNAME,
    port = PORT,
    db = DATABASE,
)

engine = create_engine(DB_URL)

Base = declarative_base(engine)

session = sessionmaker(engine)()


# 第一步：创建一个ORM模型
from sqlalchemy import Column,Integer,String,DECIMAL,Boolean,Enum,Date,DateTime,Time,Text
from sqlalchemy.dialects.mysql import LONGTEXT
import enum,datetime
class TagEnum(enum.Enum):
    python = "python"
    java = "java"
    django = "diango"

class Person(Base):
    __tablename__ = 'person' # 表名
    id = Column(Integer,primary_key=True,autoincrement=True)
    name = Column(String(50))
    age = Column(Integer)
    country = Column(String(20))
    # DECIMAL(总位数，小数点后的位数)
    price = Column(DECIMAL(20,9))
    # 布尔类型
    is_delete = Column(Boolean)
    # 枚举类型方式一
    tag1 = Column(Enum("python",'java','php'))
    # 枚举类型方式二
    tag2 = Column(Enum(TagEnum))
    # 时间
    # 2017-10-05
    create_time1 = Column(Date)
    # 2017-10-05 23:26:58
    create_time2 = Column(DateTime)
    # 23:26:58
    create_time3 = Column(Time)
    # 文本类型
    content = Column(Text)
    lcontent = Column(LONGTEXT)

# 删除数据表 === 删除数据库表
Base.metadata.drop_all()
# 创建数据表 === 只会映射一次到数据库中
Base.metadata.create_all()

per = Person(
    name = 'xxx',
    age = 18,
    country = 66,
    price = 6.555555555,
    is_delete = True,
    tag1 = "python",
    tag2 = TagEnum.python,
    create_time1 = datetime.date(2017,10,5),
    create_time2 = datetime.datetime(2017,10,5,23,26,58),
    create_time3 = datetime.time(23,26,58),
    content = "我可以存储6万多个字符串",
    lcontent = "我比6万多个字符串还多"
)
session.add(per)
session.commit()

 四、Column常用参数

1.default：默认值
2.nullable：是否为空
3.primary_key：是否为主键
4.unique：是否唯一
5.autoincrement：是否自动增长
6.onupdate：更新的时候执行的函数
7.name：该属性再数据库中的字段映射

from sqlalchemy import create_engine
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import sessionmaker

HOSTNAME = '127.0.0.1'
PORT = 3306
DATABASE = 'demo'
USERNAME = 'root'
PASSWORD = '123456'

# 链接数据库的字符串，固定格式
DB_URL = "mysql+pymysql://{username}:{password}@{host}:{port}/{db}?charset=utf8".format(
    username = USERNAME,
    password = PASSWORD,
    host = HOSTNAME,
    port = PORT,
    db = DATABASE,
)

engine = create_engine(DB_URL)

Base = declarative_base(engine)

session = sessionmaker(engine)()


# 第一步：创建一个ORM模型
from sqlalchemy import Column,Integer,String,DateTime
from datetime import datetime
class Person(Base):
    __tablename__ = 'person' # 表名
    id = Column(Integer,primary_key=True,autoincrement=True)
    # 数据库字段名就变成了my_title
    title = Column(String(50),name="my_title",nullable=False)
    create_time = Column(DateTime,default=datetime.now())
    update_date = Column(DateTime,onupdate=datetime.now)
    read_count = Column(Integer,default=0,nullable=False)

# 删除数据表 === 删除数据库表
Base.metadata.drop_all()
# 创建数据表 === 只会映射一次到数据库中
Base.metadata.create_all()

# 添加数据
per = Person(title = "aaa")
session.add(per)
session.commit()

# 修改数据 === 测试onupdate，只有更新时update_date字段才有数据修改
# p = session.query(Person).first()
# p.title = "s5s5"
# session.commit()

 五、query可用参数

# 模型对象
# aces = session.query(Article).all()
# print(aces)

# 模型属性
# aces = session.query(Article.title,Article.price).all()
# print(aces)

# 聚合函数
from sqlalchemy import func
aces = session.query(func.count(Article.id)).first()
print('行数量',aces)
aces1 = session.query(func.avg(Article.price)).first()
print('求平均值',aces1)
aces2 = session.query(func.max(Article.price)).first()
print('求最大值',aces2)
aces3 = session.query(func.min(Article.price)).first()
print('求最小值',aces3)
aces4 = session.query(func.sum(Article.price)).first()
print('求和',aces4)

六、filter过滤条件

# equal
a1 = session.query(Article).filter(Article.id == 1).first()
# not equal
a2 = session.query(Article).filter(Article.id != 1).all()
# like && ilike（不区分大小写）
a3 = session.query(Article).filter(Article.title.like('title%')).all()
# in
a4 = session.query(Article).filter(Article.title.in_(['title0','title2'])).all()
# not in
a5 = session.query(Article).filter(~Article.title.in_(['title0','title2'])).all()
# is null
a6 = session.query(Article).filter(Article.content == None).all()
# is not null
a7 = session.query(Article).filter(Article.content != None).all()
# and
from sqlalchemy import and_
a81 = session.query(Article).filter(and_(Article.title == 'aaa',Article.content == 'aaa')).all()
a82 = session.query(Article).filter(Article.title == 'aaa',Article.content == 'aaa').all()
# or
from sqlalchemy import or_
a9 = session.query(Article).filter(or_(Article.title == 'aaa',Article.content == 'aaa')).all()

 八、1对N的关系创建

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

HOSTNAME = '127.0.0.1'
PORT = 3306
DATABASE = 'demo'
USERNAME = 'root'
PASSWORD = '123456'

# 链接数据库的字符串，固定格式
DB_URL = "mysql+pymysql://{username}:{password}@{host}:{port}/{db}?charset=utf8".format(
    username = USERNAME,
    password = PASSWORD,
    host = HOSTNAME,
    port = PORT,
    db = DATABASE,
)

engine = create_engine(DB_URL)

Base = declarative_base(engine)

session = sessionmaker(engine)()

# 用户表
class User(Base):
    __tablename__ = 'user'
    id = Column(Integer,primary_key=True,autoincrement=True)
    username = Column(String(50),nullable=False)

# 文章表
class Article(Base):
    __tablename__ = 'article'
    id = Column(Integer,primary_key=True,autoincrement=True)
    title = Column(String(50),nullable=False)
    content = Column(Text,nullable=False)
    uid = Column(Integer,ForeignKey("user.id",ondelete="CASCADE"))

    # 创建（N对1）或（1对n）的关系 Article1，Article2 ===》 User
    author = relationship("User",backref = "articles")
    def __repr__(self):
        return "Article_title=%s"%self.title

# 删除数据表 === 删除数据库表
Base.metadata.drop_all()
# 创建数据表 === 只会映射一次到数据库中
Base.metadata.create_all()


# 1个用户对个文章
"""  将文章添加到用户对象中去
# 创建用户对象
u = User(username = "小海椒")
# 创建两个文章对象
a1 = Article(title = "t1",content='11111111111111111111')
a2 = Article(title = "t2",content='22222222222222222222')
# 将文章分别添加到用户对象中
u.articles.append(a1)
u.articles.append(a2)
# 将用户对象添加到session中
session.add(u)
session.commit()
"""

""" 将用户添加到文章对象中去
u = User(username = "小海椒2")
a = Article(title = "t3",content = "33333333333333")
a.author = u

session.add(a)
session.commit()
"""

九、1对1的创建关系

from sqlalchemy import create_engine
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import sessionmaker,relationship

HOSTNAME = '127.0.0.1'
PORT = 3306
DATABASE = 'demo'
USERNAME = 'root'
PASSWORD = '123456'

# 链接数据库的字符串，固定格式
DB_URL = "mysql+pymysql://{username}:{password}@{host}:{port}/{db}?charset=utf8".format(
    username = USERNAME,
    password = PASSWORD,
    host = HOSTNAME,
    port = PORT,
    db = DATABASE,
)

engine = create_engine(DB_URL)

Base = declarative_base(engine)

session = sessionmaker(engine)()

from sqlalchemy import Column,Integer,String,Text,ForeignKey

from sqlalchemy.orm import backref

# 用户表
class User(Base):
    __tablename__ = 'user'
    id = Column(Integer,primary_key=True,autoincrement=True)
    username = Column(String(50),nullable=False)

# 用户信息表
class UserExtend(Base):
    __tablename__ = 'user_extend'
    id = Column(Integer, primary_key=True, autoincrement=True)
    school = Column(String(50))
    uid = Column(Integer,ForeignKey('user.id'))

    # 创建1对1的关系
    user = relationship("User",backref = backref("extend",uselist=False))


# 删除数据表 === 删除数据库表
Base.metadata.drop_all()
# 创建数据表 === 只会映射一次到数据库中
Base.metadata.create_all()

# 1个用户对1个用户信息
u = User(username = "小黑")
extend1 = UserExtend(school="北京广播电视大学")

u.extend = extend1
session.add(u)
session.commit()

十、多对多的创建关系

from sqlalchemy import create_engine
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import sessionmaker,relationship,backref

HOSTNAME = '127.0.0.1'
PORT = 3306
DATABASE = 'demo'
USERNAME = 'root'
PASSWORD = '123456'

# 链接数据库的字符串，固定格式
DB_URL = "mysql+pymysql://{username}:{password}@{host}:{port}/{db}?charset=utf8".format(
    username = USERNAME,
    password = PASSWORD,
    host = HOSTNAME,
    port = PORT,
    db = DATABASE,
)

engine = create_engine(DB_URL)

Base = declarative_base(engine)

session = sessionmaker(engine)()

from sqlalchemy import Column,Integer,String,ForeignKey,Table

article_tag = Table(
    "article_tag",  # 表名
    Base.metadata,
    Column('article_id',Integer,ForeignKey("article.id"),primary_key=True),
    Column('tag_id',Integer,ForeignKey("tag.id"),primary_key=True)
)

# 文章表
class Article(Base):
    __tablename__ = 'article'
    id = Column(Integer,primary_key=True,autoincrement=True)
    title = Column(String(50),nullable=False)

    # tags = relationship("Tag",backref='articles',secondary=article_tag)


# 文章标签
class Tag(Base):
    __tablename__ = 'tag'
    id = Column(Integer,primary_key=True,autoincrement=True)
    name = Column(String(50),nullable=False)

    articles = relationship("Article",backref='tags',secondary=article_tag)

# # # # 删除数据表 === 删除数据库表
# Base.metadata.drop_all()
# # # # 创建数据表 === 只会映射一次到数据库中
# Base.metadata.create_all()


"""
1、定义两个多对多的模型
2、使用Table定义一个中间表(包含两个模型的外键字段并做复合主键)
3、随便再两个需要做多对多模型中选择一个定义relationship属性来绑定三者关系
例：再Article模型中
    tags = relationship("Tag",backref='articles',secondary=article_tag)
"""

# 多对多添加数据
# a1 = Article(title="Scrapy能用于那些地方？")
# a2 = Article(title="Flask和Django哪个更适用于web开发？")
#
# t1 = Tag(name='python')
# t2 = Tag(name='flask')
#
# a1.tags.append(t1)
# a1.tags.append(t2)
#
# a2.tags.append(t1)
# a2.tags.append(t2)
#
# session.add(a1)
# session.add(a2)
#
# session.commit()


# 多对多查询
a = session.query(Article).first()
for i in a.tags:
    print(i.name)

t = session.query(Tag).first()
print(t.articles)

 十一、排序的三种方式

为防止每次都需要连接数据库代码做出文件分离:DB/db.py

from sqlalchemy import create_engine
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import sessionmaker

HOSTNAME = '127.0.0.1'
PORT = 3306
DATABASE = 'db_demo'
USERNAME = 'root'
PASSWORD = '123456'

# 链接数据库的字符串，固定格式
DB_URL = "mysql+pymysql://{username}:{password}@{host}:{port}/{db}?charset=utf8".format(
    username = USERNAME,
    password = PASSWORD,
    host = HOSTNAME,
    port = PORT,
    db = DATABASE,
)

engine = create_engine(DB_URL)

Base = declarative_base(engine)

session = sessionmaker(engine)()

三种方式：

from sqlalchemy import Column,Integer,String,DateTime,ForeignKey
from sqlalchemy.orm import relationship,backref
from DB.db import session,Base
from datetime import datetime

class User(Base):
    __tablename__='user'
    id = Column(Integer,primary_key=True,autoincrement=True)
    name = Column(String(50),nullable=False)

# 文章表
class Article(Base):
    __tablename__ = 'article'
    id = Column(Integer,primary_key=True,autoincrement=True)
    title = Column(String(50),nullable=False)
    create_time = Column(DateTime,default=datetime.now(),nullable=False)
    uid = Column(Integer,ForeignKey("user.id"))
    # 方式三：可以在创建外键关系时通过backref参数指定字段排序方式
    author = relationship(
        "User",
        backref=backref(
            'articles',
            order_by=create_time.desc()
        )
    )
    # 方式二：可以指定查询排序方式
    # __mapper_args__ ={
    #     "order_by":create_time.desc()
    # }

    def __repr__(self):
        return "<article {} {} {}>".format(self.id,self.title,self.create_time)

def db_init():
    # # # # 删除数据表 === 删除数据库表
    Base.metadata.drop_all()
    # # # # 创建数据表 === 只会映射一次到数据库中
    Base.metadata.create_all()

def add_article(title):
    # 添加数据
    article = Article(title=title)
    session.add(article)
    session.commit()

def add_article2():
    article1 = Article(title='ccccccccc')
    article2 = Article(title='ddddddddd')
    user = User(name='小红')

    user.articles = [article1,article2]
    session.add(user)
    session.commit()

if __name__ == '__main__':
    # db_init()

    # add_article('xxx6')

    # add_article2()

    # 第一种方式:代码中指定排序方式
    # 正序排序
    # articles1 = session.query(Article).order_by(Article.create_time).all()

    # 倒序排序
    # articles3 = session.query(Article).order_by(Article.create_time.desc()).all()

    # 第二中方式:模型中指定排序方式
    """
    __mapper_args__ ={
        "order_by":create_time.desc()
    }
    """
    # articles4 = session.query(Article).all()


    # 第三种方式：
    """
    author = relationship(
        "User",
        backref=backref(
            'articles',
            order_by=create_time.desc()
        )
    )
    """
    u = session.query(User).first()
    print(u.articles)

 十二、limit、offset，slice、切片

from sqlalchemy import Column,Integer,String,DateTime,ForeignKey
from sqlalchemy.orm import relationship,backref
from DB.db import session,Base
from datetime import datetime

# 文章表
class Article(Base):
    __tablename__ = 'article'
    id = Column(Integer,primary_key=True,autoincrement=True)
    title = Column(String(50),nullable=False)
    create_time = Column(DateTime,default=datetime.now(),nullable=False)

    def __repr__(self):
        return "<Article {}>".format(self.title)

def db_init():
    # # # # 删除数据表 === 删除数据库表
    Base.metadata.drop_all()
    # # # # 创建数据表 === 只会映射一次到数据库中
    Base.metadata.create_all()

def add_article():
    # 添加数据
    for item in range(99):
        article = Article(title="文章标题{}".format(item))
        session.add(article)

    session.commit()

if __name__ == '__main__':
    # db_init()

    # add_article()

    # limit：可以查找的时候限制只查找几条 1-10
    articles1 = session.query(Article).limit(10).all()
    # offset：可以限制查找数据的时候过滤前面多少条 倒叙10-20
    articles2 = session.query(Article).order_by(Article.id.desc()).offset(10).limit(10).all()
    # 切片：可以对query对象使用切片来确定想要拿到的数据 倒叙最后10条数据
    articles3 = session.query(Article).order_by(Article.id.desc()).slice(0, 10).all()
    articles4 = session.query(Article).order_by(Article.id.desc())[0:10]

十三、查询懒加载

from sqlalchemy import Column,Integer,String,DateTime,ForeignKey
from sqlalchemy.orm import relationship,backref
from DB.db import session,Base
from datetime import datetime

class User(Base):
    __tablename__ = "user"
    id = Column(Integer,primary_key=True,autoincrement=True)
    name = Column(String(50),nullable=False)

# 文章表
class Article(Base):
    __tablename__ = 'article'
    id = Column(Integer,primary_key=True,autoincrement=True)
    title = Column(String(50),nullable=False)
    create_time = Column(DateTime,default=datetime.now(),nullable=False)
    uid = Column(Integer,ForeignKey("user.id"))

    articles = relationship("User",backref= backref("articles",lazy="dynamic"))

    def __repr__(self):
        return "<Article {}>".format(self.title)

def db_init():
    # # # # 删除数据表 === 删除数据库表
    Base.metadata.drop_all()
    # # # # 创建数据表 === 只会映射一次到数据库中
    Base.metadata.create_all()

def add_data():
    # 添加数据
    u = User(name="小黑")

    article_li = []
    for item in range(100):
        article_li.append(Article(title="文章标题{}".format(item)))
    u.articles = article_li
    session.add(u)
    session.commit()

if __name__ == '__main__':
    # db_init()
    # add_data()

    u = session.query(User).first()
    # AppenderQuery对象继承Query可以使用Query的所有方法对sql进行过滤
    res = u.articles.filter(Article.id<10).all()
    # 并且处理查询，也可以使用这个Query对象继续添加数据
    u.articles.append(Article(title="文章标题{}".format(1000)))
    session.add(u)
    session.commit()

 十四、group_by and having

from sqlalchemy import Column,Integer,String,DateTime,ForeignKey,Enum,func
from sqlalchemy.orm import relationship,backref
from DB.db import session,Base
from datetime import datetime

class User(Base):
    __tablename__ = "user"
    id = Column(Integer,primary_key=True,autoincrement=True)
    name = Column(String(50),nullable=False)
    age = Column(Integer,default=0)
    gender = Column(Enum("male","female","secert"))

def db_init():
    # # # # 删除数据表 === 删除数据库表
    Base.metadata.drop_all()
    # # # # 创建数据表 === 只会映射一次到数据库中
    Base.metadata.create_all()

def add_data():
    # 添加数据
    u1 = User(name="小河", age=18, gender="male")
    u2 = User(name="小马", age=18, gender="female")
    u3 = User(name="张三", age=19, gender="female")
    u4 = User(name="黑核", age=25, gender="secert")
    u5 = User(name="流弊", age=36, gender="male")

    session.add_all([u1, u2, u3, u4, u5])
    session.commit()

if __name__ == '__main__':
    # db_init()
    # add_data()

    # group_by === [(18, 2), (19, 1), (25, 1), (36, 1)]
    a = session.query(User.age,func.count(User.id)).group_by(User.age).all()

    # having === [(18, 2), (19, 1)]
    b = session.query(User.age,func.count(User.id)).group_by(User.age).having(User.age<25).all()

十五、联表查询 -- join

from sqlalchemy import Column,Integer,String,DateTime,ForeignKey,Enum,func
from sqlalchemy.orm import relationship,backref
from DB.db import session,Base
from datetime import datetime

class User(Base):
    __tablename__ = "user"
    id = Column(Integer,primary_key=True,autoincrement=True)
    name = Column(String(50),nullable=False)


class Article(Base):
    __tablename__ = "article"
    id = Column(Integer,primary_key=True,autoincrement=True)
    title = Column(String(50),nullable=False)
    create_time = Column(DateTime,nullable=False,default=datetime.now)
    uid = Column(Integer,ForeignKey('user.id'))

    articles = relationship("User",backref = backref('articles'))

def db_init():
    # # # # 删除数据表 === 删除数据库表
    Base.metadata.drop_all()
    # # # # 创建数据表 === 只会映射一次到数据库中
    Base.metadata.create_all()

def add_data():
    # 添加数据
    u1 = User(name="小河")
    u2 = User(name="小马")

    for i in range(10):
        a = Article(title='xxx{}'.format(i))
        a.articles = u1
        session.add(a)
    session.commit()

    for i in range(7):
        a = Article(title='xxx{}'.format(i))
        a.articles = u2
        session.add(a)
    session.commit()


    session.add_all([u1, u2])
    session.commit()

if __name__ == '__main__':
    # db_init()
    # add_data()

    # 找到所有用户，按照发表的文章数量进行排序
    res = session.query(
        User.name,
        func.count(Article.id)
    ).join(
        Article,
        Article.uid == User.id
    ).group_by(
        User.id
    ).order_by(
        func.count(Article.id).desc()
    ).all()

    print(res)

十六、子查询使用 -- subquery

from sqlalchemy import Column,Integer,String,DateTime,ForeignKey,Enum,func
from sqlalchemy.orm import relationship,backref
from DB.db import session,Base
from datetime import datetime

class User(Base):
    __tablename__ = "user"
    id = Column(Integer,primary_key=True,autoincrement=True)
    name = Column(String(50),nullable=False)
    city = Column(String(50),nullable=False)
    age = Column(Integer,default=0)

    def __repr__(self):
        return "< User {}>".format(self.name)


def db_init():
    # # # # 删除数据表 === 删除数据库表
    Base.metadata.drop_all()
    # # # # 创建数据表 === 只会映射一次到数据库中
    Base.metadata.create_all()

def add_data():
    # 添加数据
    u1 = User(name="小河",city="重庆",age=18)
    u2 = User(name="小白",city="北京",age=19)
    u3 = User(name="小红",city="河北",age=17)
    u4 = User(name="小慧",city="重庆",age=18)
    u5 = User(name="小黑",city="江苏",age=20)

    session.add_all([u1, u2,u3,u4,u5])
    session.commit()

if __name__ == '__main__':
    # db_init()
    # add_data()

# 寻找小河同城同年龄的人
    u = session.query(User).filter(User.name=='小河').first()
    us = session.query(User).filter(User.age == u.age,User.city == u.city).all()

# subquery实现子查询
    # 设置子查询语句
    subs = session.query(
        User.name.label('name'),
        User.city.label('city'),
        User.age.label('age')
    ).filter(
        User.name == "小河"
    ).subquery()

    # c是column的简写固定属性
    result = session.query(
        User
    ).filter(
        User.city == subs.c.city,
        User.age == subs.c.age
    ).all()

    print(result)
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原文地址：https://www.cnblogs.com/lee-xingxing/p/12372923.html