Result initial introduction

This builds on cc718cccc0bf8a01abdf4068c7ea4f3 which moved
RowProxy to Row, allowing Row to be more like a named tuple.

- KeyedTuple in ORM is replaced with Row

- ResultSetMetaData broken out into "simple" and "cursor" versions
  for ORM and Core, as well as LegacyCursor version.

- Row now has _mapping attribute that supplies full mapping behavior.
Row and SimpleRow both have named tuple behavior otherwise.
LegacyRow has some mapping features on the tuple which emit
deprecation warnings (e.g. keys(), values(), etc).   the biggest
change for mapping->tuple is the behavior of __contains__ which
moves from testing of "key in row" to "value in row".

- ResultProxy breaks into ResultProxy and FutureResult (interim),
the latter has the newer APIs.   Made available to dialects
using execution options.

- internal reflection methods and most tests move off of implicit
Row mapping behavior and move to row._mapping, result.mappings()
method using future result

- a new strategy system for cursor handling replaces the various
subclasses of RowProxy

- some execution context adjustments. We will leave EC in but
refined things like get_result_proxy() and out parameter handling.
Dialects for 1.4 will need to adjust from get_result_proxy()
to get_result_cursor_strategy(), if they are using this method

- out parameter handling now accommodated by get_out_parameter_values()
EC method.   Oracle changes for this.  external dialect for
DB2 for example will also need to adjust for this.

- deprecate case_insensitive flag for engine / result, this
feature is not used

mapping-methods on Row are deprecated, and replaced with
Row._mapping.<meth>, including:

   row.keys()  -> use row._mapping.keys()
   row.items()  -> use row._mapping.items()
   row.values() -> use row._mapping.values()
   key in row  -> use key in row._mapping
   int in row  -> use int < len(row)

Fixes: #4710
Fixes: #4878
Change-Id: Ieb9085e9bcff564359095b754da9ae0af55679f0

1 files changed, 32 insertions, 1 deletions

diff --git a/lib/sqlalchemy/sql/selectable.py b/lib/sqlalchemy/sql/selectable.py
index b2ec32c13..2cb5f8390 100644
--- a/lib/sqlalchemy/sql/selectable.py
+++ b/lib/sqlalchemy/sql/selectable.py
@@ -3180,6 +3180,36 @@ class Select(
 
     @classmethod
     def _create_select(cls, *entities):
+        r"""Construct a new :class:`.Select` using the 2.x style API.
+
+        .. versionadded:: 2.0 - the :func:`.future.select` construct is
+           the same construct as the one returned by
+           :func:`.sql.expression.select`, except that the function only
+           accepts the "columns clause" entities up front; the rest of the
+           state of the SELECT should be built up using generative methods.
+
+        Similar functionality is also available via the
+        :meth:`.FromClause.select` method on any :class:`.FromClause`.
+
+        .. seealso::
+
+            :ref:`coretutorial_selecting` - Core Tutorial description of
+            :func:`.select`.
+
+        :param \*entities:
+          Entities to SELECT from.  For Core usage, this is typically a series
+          of :class:`.ColumnElement` and / or :class:`.FromClause`
+          objects which will form the columns clause of the resulting
+          statement.   For those objects that are instances of
+          :class:`.FromClause` (typically :class:`.Table` or :class:`.Alias`
+          objects), the :attr:`.FromClause.c` collection is extracted
+          to form a collection of :class:`.ColumnElement` objects.
+
+          This parameter will also accept :class:`.Text` constructs as
+          given, as well as ORM-mapped classes.
+
+        """
+
         self = cls.__new__(cls)
         self._raw_columns = [
             coercions.expect(roles.ColumnsClauseRole, ent)
@@ -3430,7 +3460,8 @@ class Select(
             "The select() function in SQLAlchemy 2.0 will accept a "
             "series of columns / tables and other entities only, "
             "passed positionally. For forwards compatibility, use the "
-            "sqlalchemy.future.select() construct."
+            "sqlalchemy.future.select() construct.",
+            stacklevel=4,
         )
 
         self._auto_correlate = correlate