Expand joins when calculating PostgreSQL "WITH FOR UPDATE OF"

Modified the :paramref:`.Select.with_for_update.of` parameter so that if a
join or other composed selectable is passed, the individual :class:`.Table`
objects will be filtered from it, allowing one to pass a join() object to
the parameter, as occurs normally when using joined table inheritance with
the ORM.  Pull request courtesy Raymond Lu.

Fixes: #4550
Co-authored-by: Mike Bayer <mike_mp@zzzcomputing.com>
Closes: #4551
Pull-request: https://github.com/sqlalchemy/sqlalchemy/pull/4551
Pull-request-sha: 452da77d154a4087d530456db1c9af207d65cef4

Change-Id: If4b7c231f7b71190d7245543959fb5c3351125a1

1 files changed, 24 insertions, 0 deletions

diff --git a/test/dialect/postgresql/test_compiler.py b/test/dialect/postgresql/test_compiler.py
index 696078cc4..13e4aaad5 100644
--- a/test/dialect/postgresql/test_compiler.py
+++ b/test/dialect/postgresql/test_compiler.py
@@ -1056,6 +1056,30 @@ class CompileTest(fixtures.TestBase, AssertsCompiledSQL):
             "WHERE mytable_1.myid = %(myid_1)s FOR UPDATE OF mytable_1",
         )
 
+        table2 = table("table2", column("mytable_id"))
+        join = table2.join(table1, table2.c.mytable_id == table1.c.myid)
+        self.assert_compile(
+            join.select(table2.c.mytable_id == 7).with_for_update(of=[join]),
+            "SELECT table2.mytable_id, "
+            "mytable.myid, mytable.name, mytable.description "
+            "FROM table2 "
+            "JOIN mytable ON table2.mytable_id = mytable.myid "
+            "WHERE table2.mytable_id = %(mytable_id_1)s "
+            "FOR UPDATE OF mytable, table2",
+        )
+
+        join = table2.join(ta, table2.c.mytable_id == ta.c.myid)
+        self.assert_compile(
+            join.select(table2.c.mytable_id == 7).with_for_update(of=[join]),
+            "SELECT table2.mytable_id, "
+            "mytable_1.myid, mytable_1.name, mytable_1.description "
+            "FROM table2 "
+            "JOIN mytable AS mytable_1 "
+            "ON table2.mytable_id = mytable_1.myid "
+            "WHERE table2.mytable_id = %(mytable_id_1)s "
+            "FOR UPDATE OF mytable_1, table2",
+        )
+
     def test_for_update_with_schema(self):
         m = MetaData()
         table1 = Table(