[Sqlalchemy-tickets] [sqlalchemy] #2836: supply distinct within subq eager load when we see that the inner query isn't loading a distinct field

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

#2836: supply distinct within subq eager load when we see that the inner query
isn't loading a distinct field
--------------------+---------------------------------------
 Reporter:  zzzeek  |           Owner:  zzzeek
     Type:  defect  |          Status:  new
 Priority:  high    |       Milestone:  0.9.0
Component:  orm     |        Severity:  minor - half an hour
 Keywords:          |  Progress State:  in progress
--------------------+---------------------------------------
 see https://github.com/zzzeek/sqlalchemy/pull/33 for current work on this.

 proposed patch:

 {{{
 #!diff
 diff --git a/lib/sqlalchemy/orm/strategies.py
 b/lib/sqlalchemy/orm/strategies.py
 index 6ca737c..23e8cb6 100644
 --- a/lib/sqlalchemy/orm/strategies.py
 +++ b/lib/sqlalchemy/orm/strategies.py
 @@ -767,8 +767,17 @@ class SubqueryLoader(AbstractRelationshipLoader):
          if not q._from_obj and entity_mapper.isa(leftmost_mapper):
              q._set_select_from([entity_mapper], False)

 +        target_cols = q._adapt_col_list(leftmost_attr)
 +
          # select from the identity columns of the outer
 -        q._set_entities(q._adapt_col_list(leftmost_attr))
 +        q._set_entities(target_cols)
 +
 +        # if target_cols refer to a non-primary key or only
 +        # part of a composite primary key, set the q as distinct
 +        for c in target_cols:
 +            if not set(target_cols).issuperset(c.table.primary_key):
 +                q._distinct = True
 +                break

          if q._order_by is False:
              q._order_by = leftmost_mapper.order_by
 }}}

 we'll try to backport an "experimental" version of this to 0.8/0.7.

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Ticket URL: <http://www.sqlalchemy.org/trac/ticket/2836>
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