- the change for #918 was of course not nearly that simple.

The "wrapping" employed by the mssql and oracle dialects using the
"iswrapper" argument was not being used intelligently by the compiler,
and the result map was being written incorrectly, using
*more* columns in the result map than were actually returned by
the statement, due to "row number" columns that are inside the
subquery.   The compiler now writes out result map on the
"top level" select in all cases
fully, and for the mssql/oracle wrapping case extracts out
the "proxied" columns in a second step, which only includes
those columns that are proxied outwards to the top level.

This change might have implications for 3rd party dialects that
might be imitating oracle's approach.   They can safely continue
to use the "iswrapper" kw which is now ignored, but they may
need to also add the _select_wraps argument as well.

4 files changed, 51 insertions, 38 deletions

diff --git a/lib/sqlalchemy/dialects/mssql/base.py b/lib/sqlalchemy/dialects/mssql/base.py
index 92d7e4ab3..a35ab80d3 100644
--- a/lib/sqlalchemy/dialects/mssql/base.py
+++ b/lib/sqlalchemy/dialects/mssql/base.py
@@ -1031,6 +1031,7 @@ class MSSQLCompiler(compiler.SQLCompiler):
             _order_by_clauses = select._order_by_clause.clauses
             limit_clause = select._limit_clause
             offset_clause = select._offset_clause
+            kwargs['_select_wraps'] = select
             select = select._generate()
             select._mssql_visit = True
             select = select.column(
@@ -1048,7 +1049,7 @@ class MSSQLCompiler(compiler.SQLCompiler):
             else:
                 limitselect.append_whereclause(
                     mssql_rn <= (limit_clause))
-            return self.process(limitselect, iswrapper=True, **kwargs)
+            return self.process(limitselect, **kwargs)
         else:
             return compiler.SQLCompiler.visit_select(self, select, **kwargs)
 
diff --git a/lib/sqlalchemy/dialects/oracle/base.py b/lib/sqlalchemy/dialects/oracle/base.py
index a5e071148..9ec84d268 100644
--- a/lib/sqlalchemy/dialects/oracle/base.py
+++ b/lib/sqlalchemy/dialects/oracle/base.py
@@ -665,8 +665,8 @@ class OracleCompiler(compiler.SQLCompiler):
         else:
             return sql.and_(*clauses)
 
-    def visit_outer_join_column(self, vc):
-        return self.process(vc.column) + "(+)"
+    def visit_outer_join_column(self, vc, **kw):
+        return self.process(vc.column, **kw) + "(+)"
 
     def visit_sequence(self, seq):
         return (self.dialect.identifier_preparer.format_sequence(seq) +
@@ -738,6 +738,7 @@ class OracleCompiler(compiler.SQLCompiler):
                 # limit=0
 
                 # TODO: use annotations instead of clone + attr set ?
+                kwargs['_select_wraps'] = select
                 select = select._generate()
                 select._oracle_visit = True
 
@@ -794,7 +795,6 @@ class OracleCompiler(compiler.SQLCompiler):
                     offsetselect._for_update_arg = select._for_update_arg
                     select = offsetselect
 
-        kwargs['iswrapper'] = getattr(select, '_is_wrapper', False)
         return compiler.SQLCompiler.visit_select(self, select, **kwargs)
 
     def limit_clause(self, select, **kw):
diff --git a/lib/sqlalchemy/engine/default.py b/lib/sqlalchemy/engine/default.py
index 9d2bbfb15..62469d720 100644
--- a/lib/sqlalchemy/engine/default.py
+++ b/lib/sqlalchemy/engine/default.py
@@ -663,7 +663,7 @@ class DefaultExecutionContext(interfaces.ExecutionContext):
         self.cursor = self.create_cursor()
         return self
 
-    @property
+    @util.memoized_property
     def result_map(self):
         if self._result_columns:
             return self.compiled.result_map
diff --git a/lib/sqlalchemy/sql/compiler.py b/lib/sqlalchemy/sql/compiler.py
index 61b6d22d0..e37fa646c 100644
--- a/lib/sqlalchemy/sql/compiler.py
+++ b/lib/sqlalchemy/sql/compiler.py
@@ -683,20 +683,18 @@ class SQLCompiler(Compiled):
                 self.post_process_text(textclause.text))
         )
 
-    def visit_text_as_from(self, taf, iswrapper=False,
-                           compound_index=0, force_result_map=False,
+    def visit_text_as_from(self, taf,
+                           compound_index=None, force_result_map=False,
                            asfrom=False,
                            parens=True, **kw):
 
         toplevel = not self.stack
         entry = self._default_stack_entry if toplevel else self.stack[-1]
 
-        populate_result_map = force_result_map or (
-            compound_index == 0 and (
-                toplevel or
-                entry['iswrapper']
-            )
-        )
+        populate_result_map = force_result_map or \
+            toplevel or \
+            (compound_index == 0 and entry.get(
+                'need_result_map_for_compound', False))
 
         if populate_result_map:
             self._ordered_columns = False
@@ -812,13 +810,16 @@ class SQLCompiler(Compiled):
                               parens=True, compound_index=0, **kwargs):
         toplevel = not self.stack
         entry = self._default_stack_entry if toplevel else self.stack[-1]
+        need_result_map = toplevel or \
+            (compound_index == 0
+                and entry.get('need_result_map_for_compound', False))
 
         self.stack.append(
             {
                 'correlate_froms': entry['correlate_froms'],
-                'iswrapper': toplevel,
                 'asfrom_froms': entry['asfrom_froms'],
-                'selectable': cs
+                'selectable': cs,
+                'need_result_map_for_compound': need_result_map
             })
 
         keyword = self.compound_keywords.get(cs.keyword)
@@ -840,8 +841,7 @@ class SQLCompiler(Compiled):
                  or cs._offset_clause is not None) and \
             self.limit_clause(cs, **kwargs) or ""
 
-        if self.ctes and \
-                compound_index == 0 and toplevel:
+        if self.ctes and toplevel:
             text = self._render_cte_clause() + text
 
         self.stack.pop(-1)
@@ -1460,7 +1460,6 @@ class SQLCompiler(Compiled):
         ]
 
     _default_stack_entry = util.immutabledict([
-        ('iswrapper', False),
         ('correlate_froms', frozenset()),
         ('asfrom_froms', frozenset())
     ])
@@ -1488,10 +1487,11 @@ class SQLCompiler(Compiled):
         return froms
 
     def visit_select(self, select, asfrom=False, parens=True,
-                     iswrapper=False, fromhints=None,
+                     fromhints=None,
                      compound_index=0,
                      force_result_map=False,
                      nested_join_translation=False,
+                     _select_wraps=None,
                      **kwargs):
 
         needs_nested_translation = \
@@ -1505,7 +1505,7 @@ class SQLCompiler(Compiled):
                 select)
             text = self.visit_select(
                 transformed_select, asfrom=asfrom, parens=parens,
-                iswrapper=iswrapper, fromhints=fromhints,
+                fromhints=fromhints,
                 compound_index=compound_index,
                 force_result_map=force_result_map,
                 nested_join_translation=True, **kwargs
@@ -1514,12 +1514,11 @@ class SQLCompiler(Compiled):
         toplevel = not self.stack
         entry = self._default_stack_entry if toplevel else self.stack[-1]
 
-        populate_result_map = force_result_map or (
-            compound_index == 0 and (
-                toplevel or
-                entry['iswrapper']
+        populate_result_map = force_result_map or \
+            toplevel or (
+                compound_index == 0 and entry.get(
+                    'need_result_map_for_compound', False)
             )
-        )
 
         if needs_nested_translation:
             if populate_result_map:
@@ -1527,7 +1526,7 @@ class SQLCompiler(Compiled):
                     select, transformed_select)
             return text
 
-        froms = self._setup_select_stack(select, entry, asfrom, iswrapper)
+        froms = self._setup_select_stack(select, entry, asfrom)
 
         column_clause_args = kwargs.copy()
         column_clause_args.update({
@@ -1553,16 +1552,34 @@ class SQLCompiler(Compiled):
         # the actual list of columns to print in the SELECT column list.
         inner_columns = [
             c for c in [
-                self._label_select_column(select,
-                                          column,
-                                          populate_result_map, asfrom,
-                                          column_clause_args,
-                                          name=name)
+                self._label_select_column(
+                    select,
+                    column,
+                    populate_result_map, asfrom,
+                    column_clause_args,
+                    name=name)
                 for name, column in select._columns_plus_names
             ]
             if c is not None
         ]
 
+        if populate_result_map and _select_wraps is not None:
+            # if this select is a compiler-generated wrapper,
+            # rewrite the targeted columns in the result map
+            wrapped_inner_columns = set(_select_wraps.inner_columns)
+            translate = dict(
+                (outer, inner.pop()) for outer, inner in [
+                    (
+                        outer,
+                        outer.proxy_set.intersection(wrapped_inner_columns))
+                    for outer in select.inner_columns
+                ] if inner
+            )
+            self._result_columns = [
+                (key, name, tuple(translate.get(o, o) for o in obj), type_)
+                for key, name, obj, type_ in self._result_columns
+            ]
+
         text = self._compose_select_body(
             text, select, inner_columns, froms, byfrom, kwargs)
 
@@ -1575,8 +1592,7 @@ class SQLCompiler(Compiled):
             if per_dialect:
                 text += " " + self.get_statement_hint_text(per_dialect)
 
-        if self.ctes and \
-                compound_index == 0 and toplevel:
+        if self.ctes and toplevel:
             text = self._render_cte_clause() + text
 
         if select._suffixes:
@@ -1603,7 +1619,7 @@ class SQLCompiler(Compiled):
         hint_text = self.get_select_hint_text(byfrom)
         return hint_text, byfrom
 
-    def _setup_select_stack(self, select, entry, asfrom, iswrapper):
+    def _setup_select_stack(self, select, entry, asfrom):
         correlate_froms = entry['correlate_froms']
         asfrom_froms = entry['asfrom_froms']
 
@@ -1622,7 +1638,6 @@ class SQLCompiler(Compiled):
 
         new_entry = {
             'asfrom_froms': new_correlate_froms,
-            'iswrapper': iswrapper,
             'correlate_froms': all_correlate_froms,
             'selectable': select,
         }
@@ -1765,7 +1780,6 @@ class SQLCompiler(Compiled):
     def visit_insert(self, insert_stmt, **kw):
         self.stack.append(
             {'correlate_froms': set(),
-             "iswrapper": False,
              "asfrom_froms": set(),
              "selectable": insert_stmt})
 
@@ -1889,7 +1903,6 @@ class SQLCompiler(Compiled):
     def visit_update(self, update_stmt, **kw):
         self.stack.append(
             {'correlate_froms': set([update_stmt.table]),
-             "iswrapper": False,
              "asfrom_froms": set([update_stmt.table]),
              "selectable": update_stmt})
 
@@ -1975,7 +1988,6 @@ class SQLCompiler(Compiled):
 
     def visit_delete(self, delete_stmt, **kw):
         self.stack.append({'correlate_froms': set([delete_stmt.table]),
-                           "iswrapper": False,
                            "asfrom_froms": set([delete_stmt.table]),
                            "selectable": delete_stmt})
         self.isdelete = True