Question

让我说有2个表的用户和设备。他们一对多。在Sql中，我可以通过以下查询解决上述问题。

SELECT
    users.*, devices.*
FROM
    users

    LEFT JOIN ( SELECT d1.*
        FROM devices as d1
        LEFT JOIN devices AS d2
             ON d1.user_id = d2.user_id AND d1.date < d2.date
        WHERE d2.user_id IS NULL ) as device_temp

    ON (users.id = device_temp.user_id)

这是我的python代码

#user_model.py

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

Base = declarative_base()

class User(Base):
    __tablename__ = 'users'

    id = Column(Integer, primary_key=True)
    first_name = Column(String(500), nullable=False)
    last_name = Column(String(250), nullable=False)

device_model.py

#device_model.py

from sqlalchemy import Column, ForeignKey, Integer, String, DateTime
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import relationship, relation
from sqlalchemy import create_engine


from user_model import User 
Base = declarative_base()

class DeviceModel(Base):
    __tablename__ = 'device'

    id = Column(Integer, primary_key=True)
    created_at = Column(DateTime(), nullable=False)
    device_id = Column(String(250), nullable=False)
    user_uid = Column(String, ForeignKey((User.id)))
    owner = relation(User, backref='user_device')

run.py

#run.py
from sqlalchemy import create_engine
from sqlalchemy.orm import sessionmaker


from user_model import User, Base
from sleep_session import SleepSession, Base
from device_model import DeviceModel, Base

engine = create_engine(connection_string)
Base.metadata.bind = engine

DBSession = sessionmaker(bind=engine)

session = DBSession()
query = session.query(User,DeviceModel).join(DeviceModel)
results = query.all()

for row in results:
        print(row.User.first_name +" "+ row.DeviceModel.device_id + " "+ str(row.DeviceModel.created_at))

我知道这种类型的问题会被多次问到，但是我无法通过SqlAlchemy ORM找到一个问题。我想要相同的结果as described here

谢谢。

Answer 1

由于是新手，所以我使用了这个问题来进行sqlalchemy。我能得到的最接近的答案是：

如果您想查看1个文件的完整可用代码，请进行编辑-我将删除样板代码

v0.4s[0]

我的答案：

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

connection_string = 'postgres://postgres:password@localhost/test'

Base = declarative_base()

class User(Base):
    __tablename__ = 'users'

    id = Column(Integer, primary_key=True)
    first_name = Column(String(500), nullable=False)
    last_name = Column(String(250), nullable=False)

class DeviceModel(Base):
    __tablename__ = 'device'

    id = Column(Integer, primary_key=True)
    created_at = Column(DateTime(), nullable=False)
    device_id = Column(String(250), nullable=False)
    user_uid = Column(Integer, ForeignKey((User.id))) # error Key columns "user_uid" and "id" are of incompatible types: character varying and integer.
    owner = relation(User, backref='user_device')


engine = create_engine(connection_string)
Base.metadata.bind = engine

#User.__table__.create(engine)
#DeviceModel.__table__.create(engine)

DBSession = sessionmaker(bind=engine)
session = DBSession()

Answer 2

from db_config import connection_string 

from sqlalchemy import create_engine ,  and_ , inspect
from sqlalchemy.orm import sessionmaker, aliased

from user_model import User, Base
from device_model import DeviceModel, Base

engine = create_engine(connection_string)
Base.metadata.bind = engine
DBSession = sessionmaker(bind=engine)    

session = DBSession()
DeviceModel_aliased = aliased(DeviceModel)

#make sub-query
query_for_latest_device = session.query(DeviceModel).\
        outerjoin(DeviceModel_aliased,
                and_(DeviceModel_aliased.user_uid == DeviceModel.user_uid,
                        DeviceModel_aliased.created_at > DeviceModel.created_at)).\
        filter(DeviceModel_aliased.id == None).\
        subquery()

use_subquery_and_join = session.query(User.first_name,latest_device).\
        join(query_for_latest_device,
            query_for_latest_device.c.user_uid == User.user_id).\
        all()

for row in join_user_and_device:
    print(row._asdict())

如何使用SqlAlchemy ORM以一对多关系联接2个表并从其他表获取最新记录

2 个答案: