Python 炼金术中的外衣_Python_Mysql_Sqlalchemy_Outer Join

Python 炼金术中的外衣

python mysql sqlalchemy

Python 炼金术中的外衣,python,mysql,sqlalchemy,outer-join,Python,Mysql,Sqlalchemy,Outer Join,我是数据库新手，正在练习基本操作。我已经在我的机器上设置了mysql、python和sqlalchemy（巨大的胜利）我已经用部门和员工编写了这个基本模式（我知道，很无聊）。我已经知道了如何进行内部连接（下面包含代码，请随意复制），但我似乎无法获得外部连接 from sqlalchemy import create_engine from sqlalchemy import Column, Integer, String, Table, Text, Date from sqlalchemy.e

我是数据库新手，正在练习基本操作。我已经在我的机器上设置了mysql、python和sqlalchemy（巨大的胜利）

我已经用部门和员工编写了这个基本模式（我知道，很无聊）。我已经知道了如何进行内部连接（下面包含代码，请随意复制），但我似乎无法获得外部连接

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

engine = create_engine('sqlite:///:memory:', echo=False)
Session = sessionmaker(bind=engine)
session = Session()

Base = declarative_base()

class Department(Base):
    __tablename__ = 'department'
    id = Column(Integer, primary_key=True)
    name = Column(String(100))

    def __init__(self, id, name):
        self.id = id
        self.name = name

class Emp(Base):
    __tablename__ = 'employee'
    id = Column(Integer, primary_key=True)
    mgr_id = Column(Integer, ForeignKey('employee.id'))
    dept_id = Column(Integer, ForeignKey('department.id'))
    name = Column(String(100))
    sal = Column(Integer)
    doj = Column(Date)

    def __init__(self,id,mgr_id,dept_id,name,sal,doj):
        self.id = id
        self.mgr_id = mgr_id
        self.dept_id = dept_id
        self.name = name
        self.sal = sal
        self.doj = doj

Base.metadata.create_all(engine)

session.add_all([Department(1,'HR'), \
                Department(2,'Engineering'), \
                Department(3,'Marketing'), \
                Department(4,'Sales'), \
                Department(5,'Logistics')])


session.add_all([Emp(1, None, 2,'Hash', 100, datetime(2012,01,01)), \
                Emp(3, 2, 1, 'Privy', 50, datetime(2012,05,01)), \
                Emp(4, 1, 1, 'Inno', 50, datetime(2012,05,01)), \
                Emp(5, 2, 2, 'Anno', 80, datetime(2012,02,01)), \
                Emp(6, 1, 2, 'Darl', 80, datetime(2012,02,11)), \
                Emp(7, 1, 3, 'Pete', 70, datetime(2012,04,16)), \
                Emp(8, 7, 3, 'Meme', 60, datetime(2012,07,26)), \
                Emp(9, 2, 4, 'Tomiti', 70, datetime(2012,07,07)), \
                Emp(10, 9, 4, 'Bhuti', 60, datetime(2012,8,24)), \
                Emp(2, 1, 2, 'Robo', 100, datetime(2012,01,01))])

print '\nDepartment names'
for instance in session.query(Department).order_by(Department.id): 
    print instance.id,instance.name

print '\nEmployee names'
for instance in session.query(Emp).order_by(Emp.id):
    print instance.id,instance.name,instance.doj

print '\nInner Join'
for d, e in session.query(Department, Emp).\
                     filter(Department.id==Emp.dept_id).\
                     all(): 
    print d.name, e.name

print '\nOuter Join' # fails in next line
for d, e in session.query(Department, Emp).\
                     outerjoin(Department.id).\
                     all(): 
    print d.name, e.name

以下是带有错误的打印输出：

nb-meagain:sqlalchemy me$ python joinsEtc.py 

Department names
1 HR
2 Engineering
3 Marketing
4 Sales
5 Logistics

Employee names
1 Hash 2012-01-01
2 Robo 2012-01-01
3 Privy 2012-05-01
4 Inno 2012-05-01
5 Anno 2012-02-01
6 Darl 2012-02-11
7 Pete 2012-04-16
8 Meme 2012-07-26
9 Tomiti 2012-07-07
10 Bhuti 2012-08-24

Inner Join
Engineering Hash
Engineering Robo
HR Privy
HR Inno
Engineering Anno
Engineering Darl
Marketing Pete
Marketing Meme
Sales Tomiti
Sales Bhuti

Outer Join
Traceback (most recent call last):
  File "joinsEtc.py", line 85, in <module>
    outerjoin(Department.id).\
  File "/Users/me/Library/Python/2.7/lib/python/site-packages/sqlalchemy/orm/query.py", line 1688, in outerjoin
    from_joinpoint=from_joinpoint)
  File "<string>", line 1, in <lambda>
  File "/Users/me/Library/Python/2.7/lib/python/site-packages/sqlalchemy/orm/query.py", line 51, in generate
    fn(self, *args[1:], **kw)
  File "/Users/me/Library/Python/2.7/lib/python/site-packages/sqlalchemy/orm/query.py", line 1768, in _join
    right_entity = onclause.property.mapper
AttributeError: 'ColumnProperty' object has no attribute 'mapper'

nb meagain:sqlalchemy me$python joinsEtc.py 部门名称 1小时 2工程 3营销 4销售 5物流员工姓名 1-2012-01-01 2机器人2012-01-01 3秘密2012-05-01 4 Inno 2012-05-01 5 Anno 2012-02-01 6 Darl 2012-02-11 7皮特2012-04-16 8模因2012-07-26 9 Tomiti 2012-07-07 10 Bhuti 2012-08-24 内连接工程散列工程机器人人力资源部人力资源创新工程安诺工程标准营销皮特营销模因托米蒂销售部布蒂销售部外接回溯（最近一次呼叫最后一次）：文件“joinsEtc.py”，第85行，在外套（部门id）\ 文件“/Users/me/Library/Python/2.7/lib/Python/site packages/sqlalchemy/orm/query.py”，第1688行，在outerjoin中 from_joinpoint=from_joinpoint）文件“”，第1行，在文件“/Users/me/Library/Python/2.7/lib/Python/site packages/sqlalchemy/orm/query.py”，第51行，在generate中 fn（自，*参数[1:]，**千瓦）文件“/Users/me/Library/Python/2.7/lib/Python/site-packages/sqlalchemy/orm/query.py”，第1768行，在右\u entity=onclause.property.mapper AttributeError:“ColumnProperty”对象没有属性“mapper” 首先，您的内部连接很可能不是一个

内部连接，而是一个WHERE
子句，导致相同的最终结果。您可以检查生成的SQL
进行验证
现在，内部/外部联接将如下所示：
print '\nInner Join2'
for d, e in session.query(Department, Emp).join(Emp):
    print d.name, e.name

print '\nOuter Join' # from Dep -> Emp
for d, e in session.query(Department, Emp).outerjoin(Emp):
    print d.name, e and e.name # NOTE: e Might be None because of the OUTER JOIN

print '\nOuter Join2' # from Emp -> Dep
for e, d in session.query(Emp, Department).outerjoin(Department):
    print e.name, d and d.name # NOTE: d Might be None because of the OUTER JOIN

可选：
此外，为了获得完整的模型，您还应该让SA模型了解这种关系：
class Department(Base):
    ...
    employees = relationship("Emp", backref="department")
    ...

class Emp(Base):
    ...
    manager = relationship("Emp", backref="team", remote_side=[id])
    ...

在这种情况下，您可以执行以下操作：
the_boss = session.query(Emp).get(1)
print the_boss.name
print the_boss.team
assert the_boss.team[0].manager == the_boss
print the_boss.department

首先，您的内部连接很可能不是内部连接
，而是导致相同最终结果的WHERE
子句。您可以检查生成的SQL
进行验证
现在，内部/外部联接将如下所示：
print '\nInner Join2'
for d, e in session.query(Department, Emp).join(Emp):
    print d.name, e.name

print '\nOuter Join' # from Dep -> Emp
for d, e in session.query(Department, Emp).outerjoin(Emp):
    print d.name, e and e.name # NOTE: e Might be None because of the OUTER JOIN

print '\nOuter Join2' # from Emp -> Dep
for e, d in session.query(Emp, Department).outerjoin(Department):
    print e.name, d and d.name # NOTE: d Might be None because of the OUTER JOIN

可选：
此外，为了获得完整的模型，您还应该让SA模型了解这种关系：
class Department(Base):
    ...
    employees = relationship("Emp", backref="department")
    ...

class Emp(Base):
    ...
    manager = relationship("Emp", backref="team", remote_side=[id])
    ...

在这种情况下，您可以执行以下操作：
the_boss = session.query(Emp).get(1)
print the_boss.name
print the_boss.team
assert the_boss.team[0].manager == the_boss
print the_boss.department

你能编辑你的问题以完整地包含实际的错误信息吗？这是包含错误信息的编辑。你能编辑你的问题以完整地包含实际的错误信息吗？这是包含错误信息的编辑。嗨，范，回答不错，但你的回答中实际上有一些例外。它们很容易修复，所以其实没什么大不了的。但是为了不发布错误的答案，你介意编辑答案的最后一部分吗？也就是说，在那里你可以打印出与你老板有关的信息。例如，老板。员工需要成为老板团队。谢谢可以，不过你可能也可以：）真的！但是我不能接受这个答案。感谢您的关注！嗨，范，回答得很好，但实际上你的回答中有一些例外。它们很容易修复，所以其实没什么大不了的。但是为了不发布错误的答案，你介意编辑答案的最后一部分吗？也就是说，在那里你可以打印出与你老板有关的信息。例如，老板。员工需要成为老板团队。谢谢可以，不过你可能也可以：）真的！但是我不能接受这个答案。感谢您的关注！