From ef7ff058eb67d73ebeac7b125ab2a7806e14629c Mon Sep 17 00:00:00 2001 From: Mike Bayer Date: Thu, 13 Jun 2019 12:37:22 -0400 Subject: 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 --- lib/sqlalchemy/sql/roles.py | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) (limited to 'lib/sqlalchemy/sql/roles.py') diff --git a/lib/sqlalchemy/sql/roles.py b/lib/sqlalchemy/sql/roles.py index 053bd7146..55c52d401 100644 --- a/lib/sqlalchemy/sql/roles.py +++ b/lib/sqlalchemy/sql/roles.py @@ -95,6 +95,8 @@ class InElementRole(SQLRole): class FromClauseRole(ColumnsClauseRole): _role_name = "FROM expression, such as a Table or alias() object" + _is_subquery = False + @property def _hide_froms(self): raise NotImplementedError() @@ -134,7 +136,7 @@ class StatementRole(CoerceTextStatementRole): class ReturnsRowsRole(StatementRole): _role_name = ( - "Row returning expression such as a SELECT, or an " + "Row returning expression such as a SELECT, a FROM clause, or an " "INSERT/UPDATE/DELETE with RETURNING" ) @@ -142,6 +144,12 @@ class ReturnsRowsRole(StatementRole): class SelectStatementRole(ReturnsRowsRole): _role_name = "SELECT construct or equivalent text() construct" + def subquery(self): + raise NotImplementedError( + "All SelectStatementRole objects should implement a " + ".subquery() method." + ) + class HasCTERole(ReturnsRowsRole): pass -- cgit v1.2.1