与特定列的SqlAlchemy关系

Question

假设我有一个类似这样的SqlAlchemy模型：

from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import Column, String, Integer, ForeignKey
from sqlalchemy.orm import sessionmaker, relationship
Base = declarative_base()
Session = sessionmaker()

class EmployeeType(Base):
    __tablename__ = 'employee_type'
    id = Column(Integer(), primary_key=True)
    name = Column(String(20))

class Employee(Base):
    __tablename__ = 'employee'
    id = Column(Integer(), primary_key=True)
    type_id = Column(Integer(), ForeignKey(EmployeeType.id))
    type = relationship(EmployeeType, uselist=False)

session = Session()
session.add(EmployeeType(name='drone'))
session.add(EmployeeType(name='PHB'))

我想从员工直接到EmployeeType.name为了方便起见，如果我有一个类型名，我可以跳过查找id或EmployeeType对象的步骤：

^{pr2}$

这样的事情有可能吗？在

编辑：我发现association_proxy可以帮我实现这一目标：

class Employee(Base):
    ...
    type_name = association_proxy("type", "name")

唯一的问题是如果我分配给它：

emp = session.query(Employee).filter_by(EmployeeType.name=='PHB').first()
emp.type_name = 'drone'

它修改了员工_类型.名称列，而不是employee.type\u id列。在

Answer 1

我会通过创建一个方法来实现这一点。在

class EmployeeType(Base):
    __tablename__ = 'employee_type'
    id = Column(Integer(), primary_key=True)
    name = Column(String(20))

class Employee(Base):
    __tablename__ = 'employee'
    id = Column(Integer(), primary_key=True)
    type_id = Column(Integer(), ForeignKey(EmployeeType.id))
    type = relationship(EmployeeType, uselist=False)

    def __init__(self, type):
        self.type = type

    def add(self, type_name=None):
        if type_name is not None:
            emp_type = DBSession.query(EmployeeType).filter(EmployeeType.name == type_name).first()
            if emp_type:
                type = emp_type
            else:
                type = EmployeeType(name=type_name)
        else:
            type = None
        DBSession.add(Employee(type=type))

然后你要：

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Answer 2

我同意Jonathan的一般方法，但是我觉得在会话中添加employee对象和设置employee类型应该是独立操作。下面是一个实现，它将type_name作为属性，并要求在设置会话之前将其添加到会话中：

from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import Column, String, Integer, ForeignKey
from sqlalchemy.orm import sessionmaker, relationship
Base = declarative_base()
Session = sessionmaker()

class EmployeeType(Base):
    __tablename__ = 'employee_type'
    id = Column(Integer(), primary_key=True)
    name = Column(String(20))

class Employee(Base):
    __tablename__ = 'employee'
    id = Column(Integer(), primary_key=True)
    type_id = Column(Integer(), ForeignKey(EmployeeType.id))
    type = relationship(EmployeeType)

    @property
    def type_name(self):
        if self.type is not None:
            return self.type.name
        return None

    @type_name.setter
    def type_name(self, value):
        if value is None:
            self.type = None
        else:
            session = Session.object_session(self)
            if session is None:
                raise Exception("Can't set Employee type by name until added to session")
            self.type = session.query(EmployeeType).filter_by(name=value).one()