This question is sparked by some trouble that I am having with deleting
model instances. Please see this
question:
http://stackoverflow.com/questions/35163325/sqlalchemy-circular-dependency-on-delete
I have set up my models like below. I have several kinds of "tests" defined
in my database. Each "test" shares certain columns like 'status', 'date',
'who preformed it', etc. Each different test type then defines columns
specific to it.
class HasID(object):
@declared_attr
def id(cls):
return Column('id', Integer, Sequence('test_id_seq'), primary_key=True)
...
class TestParent(HasID, Model)
__tablename__ = 'tests'
discriminator = Column(String(50))
__mapper_args__ = {'polymorphic_on': discriminator}
...
class FooTest(TestParent, Model):
__tablename__ = 'footests'
__mapper_args__ = {'polymorphic_identity': 'footests'}
id = Column(Integer, ForeignKey('tests.id'), primary_key=True)
parent_id = Column(Integer, ForeignKey('footests.id'))
children = relationship('FooTest',
foreign_keys='FooTest.id',
lazy='joined',
join_depth=2,
cascade='save-update, merge, delete, delete-orphan')
...
class BarTest(TestParent, Model):
__tablename__ = 'bartests'
__mapper_args__ = {'polymorphic_identity': 'bartests'}
id = Column(Integer, ForeignKey('tests.id'), primary_key=True)
...
Now, I am wondering if this is a correct way to set up the FooTest, as one
instance of FooTest may have several child instances of FooTest as
children.
I am unable to delete any test instance (BarTest or otherwise) and am
getting a circular dependency error referring to the FooTest table.
Am I missing any fundamental concepts related to table inheritance?
Thanks everyone,
Brian Leach
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