apply asbool reduction to the onclause in join()

The :func:`.true` and :func:`.false` operators may now be applied as the
"onclause" of a :func:`.sql.join` on a backend that does not support
"native boolean" expressions, e.g. Oracle or SQL Server, and the expression
will render as "1=1" for true and "1=0" false.  This is the behavior that
was introduced many years ago in :ticket:`2804` for and/or expressions.

Change-Id: I85311c31c22d6e226c618f8840f6b95eca611153

1 files changed, 37 insertions, 0 deletions

diff --git a/test/sql/test_operators.py b/test/sql/test_operators.py
index aa56d0b6b..a90b03b38 100644
--- a/test/sql/test_operators.py
+++ b/test/sql/test_operators.py
@@ -5,6 +5,7 @@ from sqlalchemy import and_
 from sqlalchemy import between
 from sqlalchemy import exc
 from sqlalchemy import Integer
+from sqlalchemy import join
 from sqlalchemy import LargeBinary
 from sqlalchemy import literal_column
 from sqlalchemy import not_
@@ -988,6 +989,42 @@ class BooleanEvalTest(fixtures.TestBase, testing.AssertsCompiledSQL):
             or_(false(), true()), "1 = 1", dialect=self._dialect(False)
         )
 
+    def test_seven_a(self):
+        t1 = table("t1", column("a"))
+        t2 = table("t2", column("b"))
+        self.assert_compile(
+            join(t1, t2, onclause=true()),
+            "t1 JOIN t2 ON 1 = 1",
+            dialect=self._dialect(False),
+        )
+
+    def test_seven_b(self):
+        t1 = table("t1", column("a"))
+        t2 = table("t2", column("b"))
+        self.assert_compile(
+            join(t1, t2, onclause=false()),
+            "t1 JOIN t2 ON 0 = 1",
+            dialect=self._dialect(False),
+        )
+
+    def test_seven_c(self):
+        t1 = table("t1", column("a"))
+        t2 = table("t2", column("b"))
+        self.assert_compile(
+            join(t1, t2, onclause=true()),
+            "t1 JOIN t2 ON true",
+            dialect=self._dialect(True),
+        )
+
+    def test_seven_d(self):
+        t1 = table("t1", column("a"))
+        t2 = table("t2", column("b"))
+        self.assert_compile(
+            join(t1, t2, onclause=false()),
+            "t1 JOIN t2 ON false",
+            dialect=self._dialect(True),
+        )
+
     def test_eight(self):
         self.assert_compile(
             and_(false(), true()), "false", dialect=self._dialect(True)