def __repr__(self):
    return "<User(name='%s',  password='%s')>" % ( self.name, self.password)

from sqlalchemy import create_engine
from sqlalchemy import Table, MetaData, Column, Integer, String
from sqlalchemy.orm import mapper, sessionmaker
# 创建实例，并连接test库
engine = create_engine("mysql+pymysql://root:123456@localhost/test",
                                    encoding='utf-8', echo=True)
metadata = MetaData()
user = Table('user', metadata,
            Column('id', Integer, primary_key=True,autoincrement=True),
            Column('name', String(50)),
            Column('password', String(12))
        )
class User(object):
    def __init__(self, name, id, password):
        self.id = id
        self.name = name
        self.password = password
    def __repr__(self):
        return "<User(name='%s',  password='%s')>" % (self.name, self.password)
mapper(User, user)
# 创建与数据库的会话session class ,注意,这里返回给session的是个class,不是实例
Session_class = sessionmaker(bind=engine)
Session = Session_class()  # 生成session实例
my_user = Session.query(User).filter_by(name="fgf").first()  # 查询第一个
# my_user = Session.query(User).filter_by().all()  # 查询所有
print(my_user)
# print(my_user.id,my_user.name,my_user.password)
# Session.commit()  #查询不需要commit

my_user1 = Session.query(User).filter(User.id>2).all()
my_user2 = Session.query(User).filter_by(id=27).all()  # filter_by相等用‘=’
my_user3 = Session.query(User).filter(User.id==27).all()  # filter相等用‘==’
objs = Session.query(User).filter(User.id>0).filter(User.id<7).all()
print(my_user1,'\n',my_user2,'\n',my_user3,'\n',objs)

几种常见sqlalchemy查询：
#简单查询    
print(session.query(User).all())
print(session.query(User.name, User.fullname).all())    
print(session.query(User, User.name).all())        
#带条件查询    
print(session.query(User).filter_by(name='user1').all())    
print(session.query(User).filter(User.name == "user").all())    
print(session.query(User).filter(User.name.like("user%")).all())      
#多条件查询  
from sqlalchemy import and_,or_  
print(session.query(User).filter(and_(User.name.like("user%"), User.fullname.like("first%"))).all())    
print(session.query(User).filter(or_(User.name.like("user%"), User.password != None)).all())        
#sql过滤    
print(session.query(User).filter("id>:id").params(id=1).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
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 func
# count User records, without
# using a subquery.
session.query(func.count(User.id))
# return count of user "id" grouped
# by "name"
session.query(func.count(User.id)).\
        group_by(User.name)
from sqlalchemy import distinct
# count distinct "name" values
session.query(func.count(distinct(User.name)))

from sqlalchemy import create_engine
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import Column, Enum,DATE,Integer, String,ForeignKey
from sqlalchemy.orm import sessionmaker,relationship
engine = create_engine("mysql+pymysql://root:123456@localhost/test",
                                    encoding='utf-8')
Base = declarative_base()  # 生成orm基类
class Stu2(Base):
    __tablename__ = "stu2"
    id = Column(Integer, primary_key=True,autoincrement=True)
    name = Column(String(32),nullable=False)
    register_date = Column(DATE,nullable=False)
    def __repr__(self):
        return "<%s name:%s>" % (self.id, self.name)
class StudyRecord(Base):
    __tablename__ = "study_record"
    id = Column(Integer, primary_key=True,autoincrement=True)
    day = Column(Integer,nullable=False)
    status = Column(String(32),nullable=False)
    stu_id = Column(Integer,ForeignKey("stu2.id"))  #------外键关联------
    #这个nb，允许你在user表里通过backref字段反向查出所有它在stu2表里的关联项数据
    stu2 = relationship("Stu2", backref="my_study_record")  # 添加关系，反查（在内存里）
    def __repr__(self):
        return "<%s day:%s status:%s>" % (self.stu2.name, self.day,self.status)
Base.metadata.create_all(engine)  # 创建表结构
Session_class = sessionmaker(bind=engine)  # 创建与数据库的会话session class ,注意,这里返回给session的是个class,不是实例
session = Session_class()  # 生成session实例 #cursor
s1 = Stu2(name="A",register_date="2014-05-21")
s2 = Stu2(name="J",register_date="2014-03-21")
s3 = Stu2(name="R",register_date="2014-02-21")
s4 = Stu2(name="E",register_date="2013-01-21")
study_obj1 = StudyRecord(day=1,status="YES", stu_id=1)
study_obj2 = StudyRecord(day=2,status="NO", stu_id=1)
study_obj3 = StudyRecord(day=3,status="YES", stu_id=1)
study_obj4 = StudyRecord(day=1,status="YES", stu_id=2)
session.add_all([s1,s2,s3,s4,study_obj1,study_obj2,study_obj3,study_obj4])  # 创建
session.commit()
stu_obj = session.query(Stu2).filter(Stu2.name=="a").first()  # 查询
# 在stu2表，查到StudyRecord表的记录
print(stu_obj.my_study_record)  # 查询A一共上了几节课

post_keywords = Table('student_class',Base.metadata,
        Column('student_id',Integer,ForeignKey('students.id')),
        Column('class_id',Integer,ForeignKey('classes.id'))
)
class Student(Base):
    __tablename__ = 'students'
    id = Column(Integer,primary_key=True)
    name = Column(String(20))
    age = Column(Integer)
    keywords = relationship('Class',secondary=student_class,backref='students')
    # keywords = relationship('Class',secondary=student_class,backref=backref('students,lazy="dynamic"),lazy="dynamic")
class Class(Base):
    __tablename__ = 'classes'
    id = Column(Integer,primary_key = True)
    classname = Column(String(50),nullable=False,unique=True)

from sqlalchemy import Integer, ForeignKey, String, Column
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import relationship
from sqlalchemy import create_engine
Base = declarative_base()
class Customer(Base):
    __tablename__ = 'customer'
    id = Column(Integer, primary_key=True,autoincrement=True)
    name = Column(String(64))
    # 账单地址和邮寄地址, 都关联同一个地址表
    billing_address_id = Column(Integer, ForeignKey("address.id"))
    shipping_address_id = Column(Integer, ForeignKey("address.id"))
    billing_address = relationship("Address", foreign_keys=[billing_address_id])
    shipping_address = relationship("Address", foreign_keys=[shipping_address_id])
class Address(Base):
    __tablename__ = 'address'
    id = Column(Integer, primary_key=True,autoincrement=True)
    street = Column(String(64))
    city = Column(String(64))
    state = Column(String(64))
    def __repr__(self):
        return self.street
engine = create_engine("mysql+pymysql://root:123456@localhost/test",
                                    encoding='utf-8')
Base.metadata.create_all(engine)  # 创建表结构

print(admin_role.id)   #->None
print(john.id)   #->None

db.session.add(admin_role)
db.session.add(mod_role)
db.session.add(user_role)
db.session.add(john)
db.session.add(susan)
db.session.add(david)
#或者一次性添加
db.session.add_all([admin_role,mod_role,user_role,john,susan,davia])
#此时这些数据对象的状态变成挂起的了，依然没有写入到数据库中，我们打印对象的id，依然是None
print(admin_role.id) #->None
#直到我们commit()之后，这些数据对象才持久化到数据库中
db.commit()
print(admin_role.id) #->1

registrations=db.Table("registrations",
    db.Column("student_id",db.Integer,db.ForeignKey("students.id")),
    db.Column("class_id",db.Integer,db.ForeignKey("classes.id"))
)
class Student(db.Model):
    id=db.Column(db.Integer,primary_key=True)
    name=db.Column(db.String(20))
    classes=db.relationship("Class",
                            secondary=registrations,
                            backref=db.backref("students",lazy="dynamic"),
                            lazy="dynamic")
class Class(db.Model):
    id=db.Column(db.Integer,primary_key=True)
    name=db.Column(db.String(20))
c=Class(name="语文")
#学生s注册了课程c
s.classes.append(c)
db.session.add(s)
s.classes.remove(c)
db.session.add(s)
#学生s注册的所有课程
s.classes.all()
#注册c的所有的学生
c.students.all()

class Follow(db.Model):
    __tablename__="follows"
    follower_id=db.Column(db.Integer,db.ForeignKey("users.id"),primary_key=True)
    followed_id=db.Column(db.Integer,db.ForeignKey("user.id"),primary_key=True)
    timestamp=db.Column(db.DateTime,default=datetime.utcnow)
class User(db.Model):
    __tablename__="users"
    username=db.Column(db.String(20),index=True)
    followed=db.relationship("Follow",
                            foreign_key=[Follow.follower_id],
                            backref=db.backref("follower",lazy="joined"),
                            lazy="dynamic",
                            cascade="all,delete-orphan")
     followers=db.relationship("Follow",
                            foreign_key=[Follow.followed_id],
                            backref=db.backref("followed",lazy="joined"),
                            lazy="dynamic",
                            cascade="all,delete-orphan")