Re: [Sqlalchemy-tickets] [sqlalchemy] #2872: AliasedClass.__getattr__() creates malformed QueryableAttribute

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

#2872: AliasedClass.__getattr__() creates malformed QueryableAttribute
---------------------------+-------------------------------
      Reporter:  elic      |      Owner:  zzzeek
          Type:  defect    |     Status:  new
      Priority:  high      |  Milestone:  0.9.0
     Component:  orm       |   Severity:  major - 1-3 hours
    Resolution:            |   Keywords:
Progress State:  in queue  |
---------------------------+-------------------------------
Changes (by zzzeek):

 * priority:  medium => high
 * milestone:  0.9.xx => 0.9.0
 * severity:  no triage selected yet => major - 1-3 hours
 * status_field:  awaiting triage => in queue


Comment:

 unusually, the verbal description of the case here gives us a test case
 simply, whereas the test case posted here is, mmm, very scary!   A
 descriptor might return a `QueryableAttribute` and we need to adapt that,
 so that suggests a simple @hybrid_proprerty needs this fix, and i think
 you are right.  Here's a patch on master:

 {{{
 #!diff
 index 9737072..74ea592 100644
 --- a/lib/sqlalchemy/orm/util.py
 +++ b/lib/sqlalchemy/orm/util.py
 @@ -341,9 +341,12 @@ class AliasedClass(object):
                  return None
          elif hasattr(attr, '__get__'):
              ret = attr.__get__(None, self)
 -            if isinstance(ret, PropComparator):
 +            if isinstance(ret, attributes.QueryableAttribute):
 +                return _aliased_insp._adapt_prop(ret, key)
 +            elif isinstance(ret, PropComparator):
                  return ret.adapt_to_entity(_aliased_insp)
 -            return ret
 +            else:
 +                return ret
          else:
              return attr
 }}}

 simple test seems to show it:

 {{{
 #!python
 from sqlalchemy import *
 from sqlalchemy.orm import *
 from sqlalchemy.ext.declarative import declarative_base
 from sqlalchemy.ext.hybrid import hybrid_property

 Base = declarative_base()

 class A(Base):
     __tablename__ = 'a'

     id = Column(Integer, primary_key=True)
     data = Column(String(50))

     @hybrid_property
     def foo_data(self):
         return self.data

 print A.foo_data

 a1 = aliased(A)

 print a1.data
 print a1.foo_data


 }}}


 otherwise the `QueryableAttribute._adapt_to_entity()` method that gets
 called otherwise here is inadequate.   At the moment it seems like that
 system should be clarified - why *cant*
 `QueryableAttribute._adapt_to_entity()` do the right thing?   I might try
 to figure out why that is.  But yes, the patch you have already is the
 immediate fix.    Not really sure about that metaclass test though, just a
 simple descriptor is all we need to illustrate?

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Ticket URL: <http://www.sqlalchemy.org/trac/ticket/2872#comment:1>
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