SelectBase no longer a FromClause

As part of the SQLAlchemy 2.0 migration project, a conceptual change has
been made to the role of the :class:`.SelectBase` class hierarchy,
which is the root of all "SELECT" statement constructs, in that they no
longer serve directly as FROM clauses, that is, they no longer subclass
:class:`.FromClause`.  For end users, the change mostly means that any
placement of a :func:`.select` construct in the FROM clause of another
:func:`.select` requires first that it be wrapped in a subquery first,
which historically is through the use of the :meth:`.SelectBase.alias`
method, and is now also available through the use of
:meth:`.SelectBase.subquery`.    This was usually a requirement in any
case since several databases don't accept unnamed SELECT subqueries
in their FROM clause in any case.

See the documentation in this change for lots more detail.

Fixes: #4617
Change-Id: I0f6174ee24b9a1a4529168e52e855e12abd60667

1 files changed, 24 insertions, 0 deletions

diff --git a/test/base/test_utils.py b/test/base/test_utils.py
index fea34cf8d..d7e4deb28 100644
--- a/test/base/test_utils.py
+++ b/test/base/test_utils.py
@@ -9,6 +9,7 @@ from sqlalchemy import sql
 from sqlalchemy import testing
 from sqlalchemy import util
 from sqlalchemy.sql import column
+from sqlalchemy.sql.base import SeparateKeyColumnCollection
 from sqlalchemy.testing import assert_raises
 from sqlalchemy.testing import assert_raises_message
 from sqlalchemy.testing import eq_
@@ -441,6 +442,29 @@ class ToListTest(fixtures.TestBase):
         )
 
 
+class SeparateKeysColumnCollectionTest(
+    testing.AssertsCompiledSQL, fixtures.TestBase
+):
+    def test_in(self):
+        cc = SeparateKeyColumnCollection()
+        cc["kcol1"] = sql.column("col1")
+        cc["kcol2"] = sql.column("col2")
+        cc["kcol3"] = sql.column("col3")
+        assert "col1" not in cc
+        assert "kcol2" in cc
+
+    def test_get(self):
+        c1, c2 = sql.column("col1"), sql.column("col2")
+        cc = SeparateKeyColumnCollection([("kcol1", c1), ("kcol2", c2)])
+        is_(cc.kcol1, c1)
+        is_(cc.kcol2, c2)
+
+    def test_all_cols(self):
+        c1, c2 = sql.column("col1"), sql.column("col2")
+        cc = SeparateKeyColumnCollection([("kcol1", c1), ("kcol2", c2)])
+        eq_(cc._all_columns, [c1, c2])
+
+
 class ColumnCollectionTest(testing.AssertsCompiledSQL, fixtures.TestBase):
     def test_in(self):
         cc = sql.ColumnCollection()