我目前使用單表繼承策略映射類層次結構（我無法使用joind）。該層次結構可能如下所示：class Parent(Base): __tablename__ = 'mytable' __mapper_args__ = { 'polymorphic_on' : type, 'polymorphic_identity' : 'parent' } id = Column(Integer, primary_key = True) type = Column(String(32), nullable = False)class Child1(Parent): __mapper_args__ = { 'polymorphic_identity' : 'child1' } property1 = Column(Integer)class Child2(Parent): __mapper_args__ = { 'polymorphic_identity' : 'child2' } property1 = Column(Integer)class Child3(Parent): __mapper_args__ = { 'polymorphic_identity' : 'child3' } other_property = Column(Integer)那么問題是，我想有一property1兩個Child1和Child2，但不是Child3。上面的當前代碼導致錯誤：sqlalchemy.exc.ArgumentError: Column 'property1' on class <class'__main__.Child2'> conflicts with existing column 'mytable.property1'我當然可以添加其他層的繼承層次這Child1與Child2從派生，并包含property1列，但Child1和Child2幾乎不相互關聯(lián)的，但我想重用這兩個類相同的數(shù)據(jù)庫列。我已經(jīng)嘗試添加property1 = Child1.property1到，Child2但沒有成功（實例值未存儲在的數(shù)據(jù)庫中Child2）誰能指出如何重用另一個子類已定義的列？
2 回答
繁星點點滴滴
TA貢獻1803條經(jīng)驗 獲得超3個贊
直接根據(jù)解決列沖突中的文檔進行改編：
from sqlalchemy import *
from sqlalchemy.orm import *
from sqlalchemy.ext.declarative import declarative_base, declared_attr
Base = declarative_base()
class Parent(Base):
__tablename__ = 'mytable'
id = Column(Integer, primary_key = True)
type = Column(String(32), nullable = False)
__mapper_args__ = {
'polymorphic_on' : type,
'polymorphic_identity' : 'parent'
}
class Child1(Parent):
__mapper_args__ = { 'polymorphic_identity' : 'child1' }
@declared_attr
def property1(cls):
return Parent.__table__.c.get('property1', Column(Integer))
class Child2(Parent):
__mapper_args__ = { 'polymorphic_identity' : 'child2' }
@declared_attr
def property1(cls):
return Parent.__table__.c.get('property1', Column(Integer))
class Child3(Parent):
__mapper_args__ = { 'polymorphic_identity' : 'child3' }
other_property = Column(Integer)
e = create_engine("sqlite://", echo=True)
Base.metadata.create_all(e)
s = Session(e)
s.add_all([Child1(property1=1), Child2(property1=2), Child3(other_property=3)])
s.commit()
for p in s.query(Parent):
if isinstance(p, (Child1, Child2)):
print p.property1
elif isinstance(p, Child3):
print p.other_property
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