- More fixes to SQLite "join rewriting"; the fix from :ticket:`2967`

implemented right before the release of 0.9.3 affected the case where
a UNION contained nested joins in it.   "Join rewriting" is a feature
with a wide range of possibilities and is the first intricate
"SQL rewriting" feature we've introduced in years, so we're sort of
going through a lot of iterations with it (not unlike eager loading
back in the 0.2/0.3 series, polymorphic loading in 0.4/0.5). We should
be there soon so thanks for bearing with us :).
fixes #2969   re: #2967
- solve the issue of join rewriting inspecting various types of
from objects without using isinstance(), by adding some new
underscored inspection flags to the FromClause hierarchy.

1 files changed, 17 insertions, 12 deletions

diff --git a/lib/sqlalchemy/sql/compiler.py b/lib/sqlalchemy/sql/compiler.py
index 148da19aa..5165ee78f 100644
--- a/lib/sqlalchemy/sql/compiler.py
+++ b/lib/sqlalchemy/sql/compiler.py
@@ -1280,13 +1280,7 @@ class SQLCompiler(Compiled):
         cloned = {}
         column_translate = [{}]
 
-        # TODO: should we be using isinstance() for this,
-        # as this whole system won't work for custom Join/Select
-        # subclasses where compilation routines
-        # call down to compiler.visit_join(), compiler.visit_select()
-        join_name = selectable.Join.__visit_name__
-        select_name = selectable.Select.__visit_name__
-        alias_name = selectable.Alias.__visit_name__
+
         def visit(element, **kw):
             if element in column_translate[-1]:
                 return column_translate[-1][element]
@@ -1296,7 +1290,7 @@ class SQLCompiler(Compiled):
 
             newelem = cloned[element] = element._clone()
 
-            if newelem.__visit_name__ is join_name and \
+            if newelem.is_selectable and newelem._is_join and \
                 isinstance(newelem.right, selectable.FromGrouping):
 
                 newelem._reset_exported()
@@ -1340,11 +1334,22 @@ class SQLCompiler(Compiled):
                 newelem.right = selectable_
 
                 newelem.onclause = visit(newelem.onclause, **kw)
-            elif newelem.__visit_name__ is alias_name \
-                and newelem.element.__visit_name__ is select_name:
-                column_translate.append({})
+
+            elif newelem.is_selectable and newelem._is_from_container:
+                # if we hit an Alias or CompoundSelect, put a marker in the
+                # stack.
+                kw['transform_clue'] = 'select_container'
+                newelem._copy_internals(clone=visit, **kw)
+            elif newelem.is_selectable and newelem._is_select:
+                barrier_select = kw.get('transform_clue', None) == 'select_container'
+                # if we're still descended from an Alias/CompoundSelect, we're
+                # in a FROM clause, so start with a new translate collection
+                if barrier_select:
+                    column_translate.append({})
+                kw['transform_clue'] = 'inside_select'
                 newelem._copy_internals(clone=visit, **kw)
-                del column_translate[-1]
+                if barrier_select:
+                    del column_translate[-1]
             else:
                 newelem._copy_internals(clone=visit, **kw)