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, 3 insertions, 1 deletions

diff --git a/lib/sqlalchemy/orm/util.py b/lib/sqlalchemy/orm/util.py
index 80d4b26b2..4b4fa4052 100644
--- a/lib/sqlalchemy/orm/util.py
+++ b/lib/sqlalchemy/orm/util.py
@@ -825,7 +825,9 @@ def aliased(element, alias=None, name=None, flat=False, adapt_on_names=False):
             raise sa_exc.ArgumentError(
                 "adapt_on_names only applies to ORM elements"
             )
-        return element._anonymous_fromclause(name=name, flat=flat)
+        return coercions.expect(
+            roles.AnonymizedFromClauseRole, element, name=name, flat=flat
+        )
     else:
         return AliasedClass(
             element,