Extract table names when comparing to nrte error

Fixed issue where the process of joining two tables could fail if one of
the tables had an unrelated, unresolvable foreign key constraint which
would raise :class:`_exc.NoReferenceError` within the join process, which
nonetheless could be bypassed to allow the join to complete. The logic
which tested the exception for signficance within the process would make
assumptions about the construct which would fail.

Fixes: sqlalchemy#5952
Change-Id: I492dacd082ddcf8abb1310ed447a6ed734595bb7

Author: zzzeek

doc/build/changelog/unreleased_13/5952.rst

@@ -0,0 +1,11 @@
+.. change::
+    :tags: bug, orm
+    :tickets: 5952
+
+    Fixed issue where the process of joining two tables could fail if one of
+    the tables had an unrelated, unresolvable foreign key constraint which
+    would raise :class:`_exc.NoReferenceError` within the join process, which
+    nonetheless could be bypassed to allow the join to complete. The logic
+    which tested the exception for signficance within the process would make
+    assumptions about the construct which would fail.
+

lib/sqlalchemy/sql/selectable.py

@@ -1229,9 +1229,12 @@ def _can_join(cls, left, right, consider_as_foreign_keys=None):
         return bool(constraints)
 
     @classmethod
+    @util.preload_module("sqlalchemy.sql.util")
     def _joincond_scan_left_right(
         cls, a, a_subset, b, consider_as_foreign_keys
     ):
+        sql_util = util.preloaded.sql_util
+
         a = coercions.expect(roles.FromClauseRole, a)
         b = coercions.expect(roles.FromClauseRole, b)
 
@@ -1251,7 +1254,8 @@ def _joincond_scan_left_right(
                 try:
                     col = fk.get_referent(left)
                 except exc.NoReferenceError as nrte:
-                    if nrte.table_name == left.name:
+                    table_names = {t.name for t in sql_util.find_tables(left)}
+                    if nrte.table_name in table_names:
                         raise
                     else:
                         continue
@@ -1270,7 +1274,8 @@ def _joincond_scan_left_right(
                     try:
                         col = fk.get_referent(b)
                     except exc.NoReferenceError as nrte:
-                        if nrte.table_name == b.name:
+                        table_names = {t.name for t in sql_util.find_tables(b)}
+                        if nrte.table_name in table_names:
                             raise
                         else:
                             continue

test/sql/test_selectable.py

@@ -1834,6 +1834,55 @@ def test_join_cond_no_such_unrelated_column(self):
         assert sql_util.join_condition(t1, t2).compare(t1.c.x == t2.c.id)
         assert sql_util.join_condition(t2, t1).compare(t1.c.x == t2.c.id)
 
+    def test_join_cond_no_such_unrelated_table_dont_compare_names(self):
+        m = MetaData()
+        t1 = Table(
+            "t1",
+            m,
+            Column("y", Integer, ForeignKey("t22.id")),
+            Column("x", Integer, ForeignKey("t2.id")),
+            Column("q", Integer, ForeignKey("t22.id")),
+        )
+        t2 = Table(
+            "t2",
+            m,
+            Column("id", Integer),
+            Column("t3id", ForeignKey("t3.id")),
+            Column("z", ForeignKey("t33.id")),
+        )
+        t3 = Table(
+            "t3", m, Column("id", Integer), Column("q", ForeignKey("t4.id"))
+        )
+
+        j1 = t1.join(t2)
+
+        assert sql_util.join_condition(j1, t3).compare(t2.c.t3id == t3.c.id)
+
+    def test_join_cond_no_such_unrelated_column_dont_compare_names(self):
+        m = MetaData()
+        t1 = Table(
+            "t1",
+            m,
+            Column("x", Integer, ForeignKey("t2.id")),
+        )
+        t2 = Table(
+            "t2",
+            m,
+            Column("id", Integer),
+            Column("t3id", ForeignKey("t3.id")),
+            Column("q", ForeignKey("t5.q")),
+        )
+        t3 = Table(
+            "t3", m, Column("id", Integer), Column("t4id", ForeignKey("t4.id"))
+        )
+        t4 = Table("t4", m, Column("id", Integer))
+        Table("t5", m, Column("id", Integer))
+        j1 = t1.join(t2)
+
+        j2 = t3.join(t4)
+
+        assert sql_util.join_condition(j1, j2).compare(t2.c.t3id == t3.c.id)
+
     def test_join_cond_no_such_related_table(self):
         m1 = MetaData()
         m2 = MetaData()