Re: [Sqlalchemy-tickets] [sqlalchemy] #2824: Add ability to query column sets as one entity

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

#2824: Add ability to query column sets as one entity
------------------------------+-------------------------------
      Reporter:  vmagamedov   |      Owner:  zzzeek
          Type:  enhancement  |     Status:  new
      Priority:  high         |  Milestone:  0.9.0
     Component:  orm          |   Severity:  major - 1-3 hours
    Resolution:               |   Keywords:
Progress State:  in progress  |
------------------------------+-------------------------------

Comment (by vmagamedov):

 I'm published my library on !GitHub:
 https://github.com/vmagamedov/sqlconstruct - it is not
 finished/polished/documented yet, but I'm already wrote some tests and
 they can help.

 Here is my Bundle subclass:
 {{{#!python
 class Construct(Bundle):

     def __init__(self, spec):
         self._spec = OrderedDict(spec)
         self._columns = tuple(set(chain(*map(_yield_columns,
 spec.values()))))
         super(Construct, self).__init__(None, *self._columns)

     def from_row(self, row):
         values_map = dict(zip(self._columns, row))
         get_value = partial(_get_value_from_map, values_map)
         return Object(zip(
             self._spec.keys(),
             map(get_value, self._spec.values()),
         ))

     def create_row_processor(self, query, procs, labels):
         def proc(row, result):
             return self.from_row([proc(row, None) for proc in procs])
         return proc
 }}}

 Some errors which are speaks for themselves:
 {{{
 ======================================================================
 ERROR: test_query_count (test_sqlconstruct.TestConstruct)
 ----------------------------------------------------------------------
 Traceback (most recent call last):
   File "/Users/vm/ws/sqlconstruct/test_sqlconstruct.py", line 336, in
 test_query_count
     self.assertEqual(query.count(), 2)
   File
 "/Users/vm/ws/sqlconstruct/.tox/py27sqla0X/src/sqlalchemy/lib/sqlalchemy/orm/query.py",
 line 2539, in count
     return self.from_self(col).scalar()
   File
 "/Users/vm/ws/sqlconstruct/.tox/py27sqla0X/src/sqlalchemy/lib/sqlalchemy/orm/query.py",
 line 952, in from_self
     q = self._from_selectable(fromclause)
   File "<string>", line 1, in <lambda>
   File
 "/Users/vm/ws/sqlconstruct/.tox/py27sqla0X/src/sqlalchemy/lib/sqlalchemy/orm/query.py",
 line 53, in generate
     fn(self, *args[1:], **kw)
   File
 "/Users/vm/ws/sqlconstruct/.tox/py27sqla0X/src/sqlalchemy/lib/sqlalchemy/orm/query.py",
 line 981, in _from_selectable
     e.adapt_to_selectable(self, self._from_obj[0])
 AttributeError: '_BundleEntity' object has no attribute
 'adapt_to_selectable'

 ======================================================================
 ERROR: test_query_with_explicit_join (test_sqlconstruct.TestConstruct)
 ----------------------------------------------------------------------
 Traceback (most recent call last):
   File "/Users/vm/ws/sqlconstruct/test_sqlconstruct.py", line 444, in
 test_query_with_explicit_join
     .join(self.b_cls.a)
   File
 "/Users/vm/ws/sqlconstruct/.tox/py27sqla0X/src/sqlalchemy/lib/sqlalchemy/orm/query.py",
 line 1673, in join
     from_joinpoint=from_joinpoint)
   File "<string>", line 1, in <lambda>
   File
 "/Users/vm/ws/sqlconstruct/.tox/py27sqla0X/src/sqlalchemy/lib/sqlalchemy/orm/query.py",
 line 53, in generate
     fn(self, *args[1:], **kw)
   File
 "/Users/vm/ws/sqlconstruct/.tox/py27sqla0X/src/sqlalchemy/lib/sqlalchemy/orm/query.py",
 line 1806, in _join
     outerjoin, create_aliases, prop)
   File
 "/Users/vm/ws/sqlconstruct/.tox/py27sqla0X/src/sqlalchemy/lib/sqlalchemy/orm/query.py",
 line 1854, in _join_left_to_right
     self._join_to_left(l_info, left, right, onclause, outerjoin)
   File
 "/Users/vm/ws/sqlconstruct/.tox/py27sqla0X/src/sqlalchemy/lib/sqlalchemy/orm/query.py",
 line 1967, in _join_to_left
     if ent.corresponds_to(left):
 AttributeError: '_BundleEntity' object has no attribute 'corresponds_to'

 ======================================================================
 ERROR: test_query_with_implicit_join_ge_08
 (test_sqlconstruct.TestConstruct)
 ----------------------------------------------------------------------
 Traceback (most recent call last):
   File "/Users/vm/ws/sqlconstruct/test_sqlconstruct.py", line 503, in
 test_query_with_implicit_join_ge_08
     .join(self.a_cls)
   File
 "/Users/vm/ws/sqlconstruct/.tox/py27sqla0X/src/sqlalchemy/lib/sqlalchemy/orm/query.py",
 line 1673, in join
     from_joinpoint=from_joinpoint)
   File "<string>", line 1, in <lambda>
   File
 "/Users/vm/ws/sqlconstruct/.tox/py27sqla0X/src/sqlalchemy/lib/sqlalchemy/orm/query.py",
 line 53, in generate
     fn(self, *args[1:], **kw)
   File
 "/Users/vm/ws/sqlconstruct/.tox/py27sqla0X/src/sqlalchemy/lib/sqlalchemy/orm/query.py",
 line 1806, in _join
     outerjoin, create_aliases, prop)
   File
 "/Users/vm/ws/sqlconstruct/.tox/py27sqla0X/src/sqlalchemy/lib/sqlalchemy/orm/query.py",
 line 1819, in _join_left_to_right
     left = self._entities[0].entity_zero_or_selectable
 AttributeError: '_BundleEntity' object has no attribute
 'entity_zero_or_selectable'
 }}}

 Other tests failed because bundles can't be selected as "single entity". I
 think that bundles can work like models: when you querying only one
 bundle, query should yield bundles and not keyed tuples with one bundle.

 Here is my custom entity wrapper with some hacks to fix tests (very
 specific, supports only Construct entities for simplicity):
 {{{#!python
 class _ConstructEntity(_QueryEntity):
     """Queryable construct entities

     Adapted from: http://www.sqlalchemy.org/trac/ticket/2824
     """
     filter_fn = id

     entities = ()
     entity_zero_or_selectable = None

     # hack for sqlalchemy.orm.query:Query class
     class mapper:
         class dispatch:
             append_result = False

     def __init__(self, query, struct):
         query._entities.append(self)
         self.struct = struct

     def corresponds_to(self, entity):
         return False

     def adapt_to_selectable(self, query, sel):
         query._entities.append(self)

     #def setup_entity(self, *args, **kwargs):
     #    raise NotImplementedError

     def setup_context(self, query, context):
         context.primary_columns.extend(self.struct.columns)

     def row_processor(self, query, context, custom_rows):
         def processor(row, result):
             struct_row = [row[c] for c in self.struct.columns]
             return self.struct.from_row(struct_row)
         return processor, None
 }}}

--
Ticket URL: <http://www.sqlalchemy.org/trac/ticket/2824#comment:10>
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