Re: [Sqlalchemy-tickets] [sqlalchemy] #2794: CircularDependencyError with jython because WeakSequence doesn't preserve order

[sqlalchemy <mi...@zz...>]

#2794: CircularDependencyError with jython because WeakSequence doesn't preserve
order
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      Reporter:  sayap            |      Owner:  zzzeek
          Type:  defect           |     Status:  new
      Priority:  medium           |  Milestone:
     Component:  utils            |   Severity:  no triage selected yet
    Resolution:                   |   Keywords:
Progress State:  awaiting triage  |
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Comment (by sayap):

 Here's some sample code that causes `CircularDependencyError` with Jython
 2.7b1+ (current hg tip 7eb5574d023d):
 {{{
 from sqlalchemy.engine import create_engine
 from sqlalchemy.ext.declarative import declarative_base
 from sqlalchemy.orm import scoped_session, sessionmaker
 from sqlalchemy.schema import Column, ForeignKey
 from sqlalchemy.types import Integer, String

 url = 'postgresql+zxjdbc://postgres@localhost/test'
 engine = create_engine(url)

 Session = scoped_session(sessionmaker())
 Session.configure(bind=engine)

 Base = declarative_base()

 class A(Base):
     __tablename__ = 'a'

     id = Column(Integer, primary_key=True)
     discriminator = Column(String(10))

     __mapper_args__ = {
         'polymorphic_on': discriminator,
         'polymorphic_identity': 'a',
     }

 class B(A):
     __tablename__ = 'b'

     __mapper_args__ = {
         'polymorphic_identity': 'b',
     }

     id = Column(Integer, ForeignKey(A.id), primary_key=True)

 class C(B):
     __tablename__ = 'c'

     __mapper_args__ = {
         'polymorphic_identity': 'c',
     }

     id = Column(Integer, ForeignKey(B.id), primary_key=True)

 Base.metadata.create_all(engine)

 c = C()
 Session.add(c)
 Session.flush()
 }}}
 In this case, the random ordering would cause
 `Mapper.self_and_descendants()` to return C first instead of A,
 subsequently causing `table_to_mapper` to have table A -> mapper C, which
 then causes the circular dependency.

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Ticket URL: <http://www.sqlalchemy.org/trac/ticket/2794#comment:2>
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