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:  medium            |  Milestone:  0.9.xx
     Component:  orm               |   Severity:  very major - up to 2 days
    Resolution:                    |   Keywords:
Progress State:  not decided upon  |
-----------------------------------+---------------------------------------
Changes (by zzzeek):

 * severity:  no triage selected yet => very major - up to 2 days


Comment:

 this is a pretty lame proof of concept but im not very comfortable with
 it, as it only would address your immediate concern which seems to be not
 a broad enough case:

 {{{
 #!diff
 diff --git a/lib/sqlalchemy/orm/loading.py b/lib/sqlalchemy/orm/loading.py
 index 512a07d..5dc1184 100644
 --- a/lib/sqlalchemy/orm/loading.py
 +++ b/lib/sqlalchemy/orm/loading.py
 @@ -42,8 +42,8 @@ def instances(query, cursor, context):
              def filter_fn(row):
                  return tuple(fn(x) for x, fn in zip(row, filter_fns))

 -    custom_rows = single_entity and \
 -                    query._entities[0].mapper.dispatch.append_result
 +    custom_rows = False #single_entity and \
 +                    #query._entities[0].mapper.dispatch.append_result

      (process, labels) = \
                  list(zip(*[
 diff --git a/lib/sqlalchemy/orm/query.py b/lib/sqlalchemy/orm/query.py
 index d64575a..01a7238 100644
 --- a/lib/sqlalchemy/orm/query.py
 +++ b/lib/sqlalchemy/orm/query.py
 @@ -2890,6 +2890,8 @@ class _QueryEntity(object):
              if not isinstance(entity, util.string_types) and \
                          _is_mapped_class(entity):
                  cls = _MapperEntity
 +            elif isinstance(entity, UserDefinedEntity):
 +                cls = _UserDefinedEntity
              else:
                  cls = _ColumnEntity
          return object.__new__(cls)
 @@ -2900,6 +2902,35 @@ class _QueryEntity(object):
          return q


 +class UserDefinedEntity(object):
 +    def setup_columns(self, column_collection, context):
 +        pass
 +
 +    def process_rows(self, context):
 +        pass
 +
 +
 +class _UserDefinedEntity(_QueryEntity):
 +    """User defined entity!"""
 +
 +    filter_fn = id
 +
 +    entities = ()
 +
 +    def __init__(self, query, entity):
 +        query._entities.append(self)
 +        self.entity = entity
 +
 +    def setup_entity(self, ext_info, aliased_adapter):
 +        raise NotImplementedError()
 +
 +    def setup_context(self, query, context):
 +        self.entity.setup_columns(context.primary_columns, context)
 +
 +    def row_processor(self, query, context, custom_rows):
 +        return self.entity.process_rows(context)
 +
 +
  class _MapperEntity(_QueryEntity):
      """mapper/class/AliasedClass entity"""

 }}}

--
Ticket URL: <http://www.sqlalchemy.org/trac/ticket/2824#comment:6>
sqlalchemy <http://www.sqlalchemy.org/>
The Database Toolkit for Python