Question

给定SQLAlchemy类的关系属性，我想确定它是指父表（外键在另一个表中），还是子表（外键在当前表中））。

例如，考虑两个类A和B，其关系为A.bs和B.a：

class B(Base):
    __tablename__ = 'b'
    id = Column(Integer, primary_key=True)
    a_id = Column(Integer, ForeignKey('a.id'))

class A(Base):
    __tablename__ = 'a'
    id = Column(Integer, primary_key=True)
    bs = relationship(B, backref='a')

在A.bs关系中，A是＆＃34;父母＆＃34;因为外键是在另一个类中。在B.a关系中，B是＆＃34;孩子＆＃34;因为外键在同一个类中。如果我有一个函数is_parent，它就会这样做：

is_parent(A.bs) == True
is_parent(B.a) == False

如何使用SQLAlchemy实现is_parent函数？

之类的东西

Answer 1

(Honestly, I can't quite imagine why you would want this, but it is more or less easy to solve looking at the structure of the class).

In [37]:

from sqlalchemy.orm.properties import ColumnProperty
from sqlalchemy.orm.relationships import RelationshipProperty 

def is_parent(obj):
    if type(obj.property) == ColumnProperty:
        return False
    if type(obj.property) == RelationshipProperty: 
        return True
    return None

print is_parent(B.a_id)
print is_parent(A.bs)

False
True

Hope it helps.

确定类是SQLAlchemy关系中的父级还是子级

1 个答案: