- The ``version_id_generator`` parameter of ``Mapper`` can now be specified

to rely upon server generated version identifiers, using triggers
or other database-provided versioning features, by passing the value
``False``.  The ORM will use RETURNING when available to immediately
load the new version identifier, else it will emit a second SELECT.
[ticket:2793]
- The ``eager_defaults`` flag of :class:`.Mapper` will now allow the
newly generated default values to be fetched using an inline
RETURNING clause, rather than a second SELECT statement, for backends
that support RETURNING.
- Added a new variant to :meth:`.ValuesBase.returning` called
:meth:`.ValuesBase.return_defaults`; this allows arbitrary columns
to be added to the RETURNING clause of the statement without interfering
with the compilers usual "implicit returning" feature, which is used to
efficiently fetch newly generated primary key values.  For supporting
backends, a dictionary of all fetched values is present at
:attr:`.ResultProxy.returned_defaults`.
- add a glossary entry for RETURNING
- add documentation for version id generation, [ticket:867]

8 files changed, 293 insertions, 224 deletions

diff --git a/lib/sqlalchemy/engine/base.py b/lib/sqlalchemy/engine/base.py
index 83fa34f2c..257eaa18a 100644
--- a/lib/sqlalchemy/engine/base.py
+++ b/lib/sqlalchemy/engine/base.py
@@ -898,6 +898,12 @@ class Connection(Connectable):
             elif not context._is_explicit_returning:
                 result.close(_autoclose_connection=False)
                 result._metadata = None
+        elif context.isupdate:
+            if context._is_implicit_returning:
+                context._fetch_implicit_update_returning(result)
+                result.close(_autoclose_connection=False)
+                result._metadata = None
+
         elif result._metadata is None:
             # no results, get rowcount
             # (which requires open cursor on some drivers
diff --git a/lib/sqlalchemy/engine/default.py b/lib/sqlalchemy/engine/default.py
index 017dfa902..90c7f5993 100644
--- a/lib/sqlalchemy/engine/default.py
+++ b/lib/sqlalchemy/engine/default.py
@@ -396,6 +396,7 @@ class DefaultExecutionContext(interfaces.ExecutionContext):
     statement = None
     postfetch_cols = None
     prefetch_cols = None
+    returning_cols = None
     _is_implicit_returning = False
     _is_explicit_returning = False
 
@@ -492,6 +493,7 @@ class DefaultExecutionContext(interfaces.ExecutionContext):
         if self.isinsert or self.isupdate:
             self.postfetch_cols = self.compiled.postfetch
             self.prefetch_cols = self.compiled.prefetch
+            self.returning_cols = self.compiled.returning
             self.__process_defaults()
 
         processors = compiled._bind_processors
@@ -750,6 +752,11 @@ class DefaultExecutionContext(interfaces.ExecutionContext):
                 ipk.append(row[c])
 
         self.inserted_primary_key = ipk
+        self.returned_defaults = row
+
+    def _fetch_implicit_update_returning(self, resultproxy):
+        row = resultproxy.fetchone()
+        self.returned_defaults = row
 
     def lastrow_has_defaults(self):
         return (self.isinsert or self.isupdate) and \
diff --git a/lib/sqlalchemy/engine/result.py b/lib/sqlalchemy/engine/result.py
index 91f3c2275..0e2316573 100644
--- a/lib/sqlalchemy/engine/result.py
+++ b/lib/sqlalchemy/engine/result.py
@@ -621,6 +621,16 @@ class ResultProxy(object):
         else:
             return self.context.compiled_parameters[0]
 
+    @property
+    def returned_defaults(self):
+        """Return the values of default columns that were fetched using
+        the ``returned_defaults`` feature.
+
+        .. versionadded:: 0.9.0
+
+        """
+        return self.context.returned_defaults
+
     def lastrow_has_defaults(self):
         """Return ``lastrow_has_defaults()`` from the underlying
         :class:`.ExecutionContext`.
diff --git a/lib/sqlalchemy/orm/mapper.py b/lib/sqlalchemy/orm/mapper.py
index fc80c4404..30b5ffc79 100644
--- a/lib/sqlalchemy/orm/mapper.py
+++ b/lib/sqlalchemy/orm/mapper.py
@@ -208,6 +208,22 @@ class Mapper(_InspectionAttr):
 
            See the section :ref:`concrete_inheritance` for an example.
 
+        :param eager_defaults: if True, the ORM will immediately fetch the
+          value of server-generated default values after an INSERT or UPDATE,
+          rather than leaving them as expired to be fetched on next access.
+          This can be used for event schemes where the server-generated values
+          are needed immediately before the flush completes.   By default,
+          this scheme will emit an individual ``SELECT`` statement per row
+          inserted or updated, which note can add significant performance
+          overhead.  However, if the
+          target database supports :term:`RETURNING`, the default values will be
+          returned inline with the INSERT or UPDATE statement, which can
+          greatly enhance performance for an application that needs frequent
+          access to just-generated server defaults.
+
+          .. versionchanged:: 0.9.0 The ``eager_defaults`` option can now
+             make use of :term:`RETURNING` for backends which support it.
+
         :param exclude_properties: A list or set of string column names to
           be excluded from mapping.
 
@@ -391,9 +407,9 @@ class Mapper(_InspectionAttr):
           thus persisting the value to the ``discriminator`` column
           in the database.
 
-          See also:
+          .. seealso::
 
-          :ref:`inheritance_toplevel`
+            :ref:`inheritance_toplevel`
 
         :param polymorphic_identity: Specifies the value which
           identifies this particular class as returned by the
@@ -419,34 +435,44 @@ class Mapper(_InspectionAttr):
            can be overridden here.
 
         :param version_id_col: A :class:`.Column`
-           that will be used to keep a running version id of mapped entities
-           in the database.  This is used during save operations to ensure that
-           no other thread or process has updated the instance during the
-           lifetime of the entity, else a
+           that will be used to keep a running version id of rows
+           in the table.  This is used to detect concurrent updates or
+           the presence of stale data in a flush.  The methodology is to
+           detect if an UPDATE statement does not match the last known
+           version id, a
            :class:`~sqlalchemy.orm.exc.StaleDataError` exception is
-           thrown.  By default the column must be of :class:`.Integer` type,
-           unless ``version_id_generator`` specifies a new generation
-           algorithm.
+           thrown.
+           By default, the column must be of :class:`.Integer` type,
+           unless ``version_id_generator`` specifies an alternative version
+           generator.
 
-        :param version_id_generator: A callable which defines the algorithm
-            used to generate new version ids. Defaults to an integer
-            generator. Can be replaced with one that generates timestamps,
-            uuids, etc. e.g.::
+           .. seealso::
 
-                import uuid
+              :ref:`mapper_version_counter` - discussion of version counting
+              and rationale.
 
-                class MyClass(Base):
-                    __tablename__ = 'mytable'
-                    id = Column(Integer, primary_key=True)
-                    version_uuid = Column(String(32))
+        :param version_id_generator: Define how new version ids should
+          be generated.  Defaults to ``None``, which indicates that
+          a simple integer counting scheme be employed.  To provide a custom
+          versioning scheme, provide a callable function of the form::
 
-                    __mapper_args__ = {
-                        'version_id_col':version_uuid,
-                        'version_id_generator':lambda version:uuid.uuid4().hex
-                    }
+              def generate_version(version):
+                  return next_version
+
+          Alternatively, server-side versioning functions such as triggers
+          may be used as well, by specifying the value ``False``.
+          Please see :ref:`server_side_version_counter` for a discussion
+          of important points when using this option.
+
+          .. versionadded:: 0.9.0 ``version_id_generator`` supports server-side
+             version number generation.
+
+          .. seealso::
+
+             :ref:`custom_version_counter`
+
+             :ref:`server_side_version_counter`
 
-            The callable receives the current version identifier as its
-            single argument.
 
         :param with_polymorphic: A tuple in the form ``(<classes>,
             <selectable>)`` indicating the default style of "polymorphic"
@@ -458,13 +484,9 @@ class Mapper(_InspectionAttr):
             indicates a selectable that will be used to query for multiple
             classes.
 
-            See also:
-
-            :ref:`concrete_inheritance` - typically uses ``with_polymorphic``
-            to specify a UNION statement to select from.
+            .. seealso::
 
-            :ref:`with_polymorphic` - usage example of the related
-            :meth:`.Query.with_polymorphic` method
+              :ref:`with_polymorphic` - discussion of polymorphic querying techniques.
 
         """
 
@@ -481,9 +503,19 @@ class Mapper(_InspectionAttr):
             self.order_by = order_by
 
         self.always_refresh = always_refresh
-        self.version_id_col = version_id_col
-        self.version_id_generator = version_id_generator or \
-                                        (lambda x: (x or 0) + 1)
+
+        if isinstance(version_id_col, MapperProperty):
+            self.version_id_prop = version_id_col
+            self.version_id_col = None
+        else:
+            self.version_id_col = version_id_col
+        if version_id_generator is False:
+            self.version_id_generator = False
+        elif version_id_generator is None:
+            self.version_id_generator = lambda x: (x or 0) + 1
+        else:
+            self.version_id_generator = version_id_generator
+
         self.concrete = concrete
         self.single = False
         self.inherits = inherits
@@ -1406,6 +1438,13 @@ class Mapper(_InspectionAttr):
     _validate_polymorphic_identity = None
 
     @_memoized_configured_property
+    def _version_id_prop(self):
+        if self.version_id_col is not None:
+            return self._columntoproperty[self.version_id_col]
+        else:
+            return None
+
+    @_memoized_configured_property
     def _acceptable_polymorphic_identities(self):
         identities = set()
 
diff --git a/lib/sqlalchemy/orm/persistence.py b/lib/sqlalchemy/orm/persistence.py
index 14970ef25..042186179 100644
--- a/lib/sqlalchemy/orm/persistence.py
+++ b/lib/sqlalchemy/orm/persistence.py
@@ -61,7 +61,7 @@ def save_obj(base_mapper, states, uowtransaction, single=False):
         if insert:
             _emit_insert_statements(base_mapper, uowtransaction,
                                     cached_connections,
-                                    table, insert)
+                                    mapper, table, insert)
 
     _finalize_insert_update_commands(base_mapper, uowtransaction,
                                     states_to_insert, states_to_update)
@@ -246,9 +246,12 @@ def _collect_insert_commands(base_mapper, uowtransaction, table,
         value_params = {}
 
         has_all_pks = True
+        has_all_defaults = True
         for col in mapper._cols_by_table[table]:
             if col is mapper.version_id_col:
-                params[col.key] = mapper.version_id_generator(None)
+                if mapper.version_id_generator is not False:
+                    val = mapper.version_id_generator(None)
+                    params[col.key] = val
             else:
                 # pull straight from the dict for
                 # pending objects
@@ -261,6 +264,9 @@ def _collect_insert_commands(base_mapper, uowtransaction, table,
                     elif col.default is None and \
                          col.server_default is None:
                         params[col.key] = value
+                    elif col.server_default is not None and \
+                        mapper.base_mapper.eager_defaults:
+                        has_all_defaults = False
 
                 elif isinstance(value, sql.ClauseElement):
                     value_params[col] = value
@@ -268,7 +274,8 @@ def _collect_insert_commands(base_mapper, uowtransaction, table,
                     params[col.key] = value
 
         insert.append((state, state_dict, params, mapper,
-                        connection, value_params, has_all_pks))
+                        connection, value_params, has_all_pks,
+                        has_all_defaults))
     return insert
 
 
@@ -315,19 +322,20 @@ def _collect_update_commands(base_mapper, uowtransaction,
                     params[col.key] = history.added[0]
                     hasdata = True
                 else:
-                    params[col.key] = mapper.version_id_generator(
-                                                params[col._label])
-
-                    # HACK: check for history, in case the
-                    # history is only
-                    # in a different table than the one
-                    # where the version_id_col is.
-                    for prop in mapper._columntoproperty.values():
-                        history = attributes.get_state_history(
-                                state, prop.key,
-                                attributes.PASSIVE_NO_INITIALIZE)
-                        if history.added:
-                            hasdata = True
+                    if mapper.version_id_generator is not False:
+                        val = mapper.version_id_generator(params[col._label])
+                        params[col.key] = val
+
+                        # HACK: check for history, in case the
+                        # history is only
+                        # in a different table than the one
+                        # where the version_id_col is.
+                        for prop in mapper._columntoproperty.values():
+                            history = attributes.get_state_history(
+                                    state, prop.key,
+                                    attributes.PASSIVE_NO_INITIALIZE)
+                            if history.added:
+                                hasdata = True
             else:
                 prop = mapper._columntoproperty[col]
                 history = attributes.get_state_history(
@@ -478,7 +486,13 @@ def _emit_update_statements(base_mapper, uowtransaction,
                     sql.bindparam(mapper.version_id_col._label,
                                     type_=mapper.version_id_col.type))
 
-        return table.update(clause)
+        stmt = table.update(clause)
+        if mapper.base_mapper.eager_defaults:
+            stmt = stmt.return_defaults()
+        elif mapper.version_id_col is not None:
+            stmt = stmt.return_defaults(mapper.version_id_col)
+
+        return stmt
 
     statement = base_mapper._memo(('update', table), update_stmt)
 
@@ -500,8 +514,7 @@ def _emit_update_statements(base_mapper, uowtransaction,
                 table,
                 state,
                 state_dict,
-                c.context.prefetch_cols,
-                c.context.postfetch_cols,
+                c,
                 c.context.compiled_parameters[0],
                 value_params)
         rows += c.rowcount
@@ -521,44 +534,55 @@ def _emit_update_statements(base_mapper, uowtransaction,
 
 
 def _emit_insert_statements(base_mapper, uowtransaction,
-                        cached_connections, table, insert):
+                        cached_connections, mapper, table, insert):
     """Emit INSERT statements corresponding to value lists collected
     by _collect_insert_commands()."""
 
     statement = base_mapper._memo(('insert', table), table.insert)
 
-    for (connection, pkeys, hasvalue, has_all_pks), \
+    for (connection, pkeys, hasvalue, has_all_pks, has_all_defaults), \
         records in groupby(insert,
                             lambda rec: (rec[4],
                                     list(rec[2].keys()),
                                     bool(rec[5]),
-                                    rec[6])
+                                    rec[6], rec[7])
     ):
-        if has_all_pks and not hasvalue:
+        if \
+            (
+                has_all_defaults
+                or not base_mapper.eager_defaults
+                or not connection.dialect.implicit_returning
+            ) and has_all_pks and not hasvalue:
+
             records = list(records)
             multiparams = [rec[2] for rec in records]
+
             c = cached_connections[connection].\
                                 execute(statement, multiparams)
 
-            for (state, state_dict, params, mapper,
-                    conn, value_params, has_all_pks), \
+            for (state, state_dict, params, mapper_rec,
+                    conn, value_params, has_all_pks, has_all_defaults), \
                     last_inserted_params in \
                     zip(records, c.context.compiled_parameters):
                 _postfetch(
-                        mapper,
+                        mapper_rec,
                         uowtransaction,
                         table,
                         state,
                         state_dict,
-                        c.context.prefetch_cols,
-                        c.context.postfetch_cols,
+                        c,
                         last_inserted_params,
                         value_params)
 
         else:
-            for state, state_dict, params, mapper, \
+            if not has_all_defaults and base_mapper.eager_defaults:
+                statement = statement.return_defaults()
+            elif mapper.version_id_col is not None:
+                statement = statement.return_defaults(mapper.version_id_col)
+
+            for state, state_dict, params, mapper_rec, \
                         connection, value_params, \
-                        has_all_pks in records:
+                        has_all_pks, has_all_defaults in records:
 
                 if value_params:
                     result = connection.execute(
@@ -574,23 +598,22 @@ def _emit_insert_statements(base_mapper, uowtransaction,
                     # set primary key attributes
                     for pk, col in zip(primary_key,
                                     mapper._pks_by_table[table]):
-                        prop = mapper._columntoproperty[col]
+                        prop = mapper_rec._columntoproperty[col]
                         if state_dict.get(prop.key) is None:
                             # TODO: would rather say:
                             #state_dict[prop.key] = pk
-                            mapper._set_state_attr_by_column(
+                            mapper_rec._set_state_attr_by_column(
                                         state,
                                         state_dict,
                                         col, pk)
 
                 _postfetch(
-                        mapper,
+                        mapper_rec,
                         uowtransaction,
                         table,
                         state,
                         state_dict,
-                        result.context.prefetch_cols,
-                        result.context.postfetch_cols,
+                        result,
                         result.context.compiled_parameters[0],
                         value_params)
 
@@ -699,14 +722,25 @@ def _finalize_insert_update_commands(base_mapper, uowtransaction,
             if readonly:
                 state._expire_attributes(state.dict, readonly)
 
-        # if eager_defaults option is enabled,
-        # refresh whatever has been expired.
+        # if eager_defaults option is enabled, load
+        # all expired cols.  Else if we have a version_id_col, make sure
+        # it isn't expired.
+        toload_now = []
+
         if base_mapper.eager_defaults and state.unloaded:
+            toload_now.extend(state.unloaded)
+        elif mapper.version_id_col is not None and \
+            mapper.version_id_generator is False:
+            prop = mapper._columntoproperty[mapper.version_id_col]
+            if prop.key in state.unloaded:
+                toload_now.extend([prop.key])
+
+        if toload_now:
             state.key = base_mapper._identity_key_from_state(state)
             loading.load_on_ident(
                 uowtransaction.session.query(base_mapper),
                 state.key, refresh_state=state,
-                only_load_props=state.unloaded)
+                only_load_props=toload_now)
 
         # call after_XXX extensions
         if not has_identity:
@@ -716,15 +750,26 @@ def _finalize_insert_update_commands(base_mapper, uowtransaction,
 
 
 def _postfetch(mapper, uowtransaction, table,
-                state, dict_, prefetch_cols, postfetch_cols,
-                            params, value_params):
+                state, dict_, result, params, value_params):
     """Expire attributes in need of newly persisted database state,
     after an INSERT or UPDATE statement has proceeded for that
     state."""
 
+    prefetch_cols = result.context.prefetch_cols
+    postfetch_cols = result.context.postfetch_cols
+    returning_cols = result.context.returning_cols
+
     if mapper.version_id_col is not None:
         prefetch_cols = list(prefetch_cols) + [mapper.version_id_col]
 
+    if returning_cols:
+        row = result.context.returned_defaults
+        if row is not None:
+            for col in returning_cols:
+                if col.primary_key:
+                    continue
+                mapper._set_state_attr_by_column(state, dict_, col, row[col])
+
     for c in prefetch_cols:
         if c.key in params and c in mapper._columntoproperty:
             mapper._set_state_attr_by_column(state, dict_, c, params[c.key])
diff --git a/lib/sqlalchemy/sql/compiler.py b/lib/sqlalchemy/sql/compiler.py
index 6370b1227..5d05cbc29 100644
--- a/lib/sqlalchemy/sql/compiler.py
+++ b/lib/sqlalchemy/sql/compiler.py
@@ -1761,11 +1761,12 @@ class SQLCompiler(Compiled):
                         '=' + c[1] for c in colparams
                         )
 
-        if update_stmt._returning:
-            self.returning = update_stmt._returning
+        if self.returning or update_stmt._returning:
+            if not self.returning:
+                self.returning = update_stmt._returning
             if self.returning_precedes_values:
                 text += " " + self.returning_clause(
-                                    update_stmt, update_stmt._returning)
+                                    update_stmt, self.returning)
 
         if extra_froms:
             extra_from_text = self.update_from_clause(
@@ -1785,7 +1786,7 @@ class SQLCompiler(Compiled):
 
         if self.returning and not self.returning_precedes_values:
             text += " " + self.returning_clause(
-                                    update_stmt, update_stmt._returning)
+                                    update_stmt, self.returning)
 
         self.stack.pop(-1)
 
@@ -1866,6 +1867,19 @@ class SQLCompiler(Compiled):
                                 self.dialect.implicit_returning and \
                                 stmt.table.implicit_returning
 
+        if self.isinsert:
+            implicit_return_defaults = implicit_returning and stmt._return_defaults
+        elif self.isupdate:
+            implicit_return_defaults = self.dialect.implicit_returning and \
+                                stmt.table.implicit_returning and \
+                                stmt._return_defaults
+
+        if implicit_return_defaults:
+            if stmt._return_defaults is True:
+                implicit_return_defaults = set(stmt.table.c)
+            else:
+                implicit_return_defaults = set(stmt._return_defaults)
+
         postfetch_lastrowid = need_pks and self.dialect.postfetch_lastrowid
 
         check_columns = {}
@@ -1928,6 +1942,10 @@ class SQLCompiler(Compiled):
                 elif c.primary_key and implicit_returning:
                     self.returning.append(c)
                     value = self.process(value.self_group())
+                elif implicit_return_defaults and \
+                    c in implicit_return_defaults:
+                    self.returning.append(c)
+                    value = self.process(value.self_group())
                 else:
                     self.postfetch.append(c)
                     value = self.process(value.self_group())
@@ -1984,14 +2002,20 @@ class SQLCompiler(Compiled):
                             not self.dialect.sequences_optional):
                             proc = self.process(c.default)
                             values.append((c, proc))
-                            if not c.primary_key:
+                            if implicit_return_defaults and \
+                                c in implicit_return_defaults:
+                                self.returning.append(c)
+                            elif not c.primary_key:
                                 self.postfetch.append(c)
                     elif c.default.is_clause_element:
                         values.append(
                             (c, self.process(c.default.arg.self_group()))
                         )
 
-                        if not c.primary_key:
+                        if implicit_return_defaults and \
+                            c in implicit_return_defaults:
+                            self.returning.append(c)
+                        elif not c.primary_key:
                             # dont add primary key column to postfetch
                             self.postfetch.append(c)
                     else:
@@ -2000,8 +2024,14 @@ class SQLCompiler(Compiled):
                         )
                         self.prefetch.append(c)
                 elif c.server_default is not None:
-                    if not c.primary_key:
+                    if implicit_return_defaults and \
+                        c in implicit_return_defaults:
+                        self.returning.append(c)
+                    elif not c.primary_key:
                         self.postfetch.append(c)
+                elif implicit_return_defaults and \
+                        c in implicit_return_defaults:
+                        self.returning.append(c)
 
             elif self.isupdate:
                 if c.onupdate is not None and not c.onupdate.is_sequence:
@@ -2009,14 +2039,25 @@ class SQLCompiler(Compiled):
                         values.append(
                             (c, self.process(c.onupdate.arg.self_group()))
                         )
-                        self.postfetch.append(c)
+                        if implicit_return_defaults and \
+                            c in implicit_return_defaults:
+                            self.returning.append(c)
+                        else:
+                            self.postfetch.append(c)
                     else:
                         values.append(
                             (c, self._create_crud_bind_param(c, None))
                         )
                         self.prefetch.append(c)
                 elif c.server_onupdate is not None:
-                    self.postfetch.append(c)
+                    if implicit_return_defaults and \
+                        c in implicit_return_defaults:
+                        self.returning.append(c)
+                    else:
+                        self.postfetch.append(c)
+                elif implicit_return_defaults and \
+                        c in implicit_return_defaults:
+                        self.returning.append(c)
 
         if parameters and stmt_parameters:
             check = set(parameters).intersection(
diff --git a/lib/sqlalchemy/sql/dml.py b/lib/sqlalchemy/sql/dml.py
index cbebf7d55..abbd05efe 100644
--- a/lib/sqlalchemy/sql/dml.py
+++ b/lib/sqlalchemy/sql/dml.py
@@ -104,9 +104,14 @@ class UpdateBase(HasPrefixes, Executable, ClauseElement):
         read the documentation notes for the database in use in
         order to determine the availability of RETURNING.
 
+        .. seealso::
+
+          :meth:`.ValuesBase.return_defaults`
+
         """
         self._returning = cols
 
+
     @_generative
     def with_hint(self, text, selectable=None, dialect_name="*"):
         """Add a table hint for a single table to this
@@ -303,6 +308,58 @@ class ValuesBase(UpdateBase):
             else:
                 self.parameters.update(kwargs)
 
+    @_generative
+    def return_defaults(self, *cols):
+        """If available, make use of a RETURNING clause for the purpose
+        of fetching server-side expressions and defaults.
+
+        When used against a backend that supports RETURNING, all column
+        values generated by SQL expression or server-side-default will be added
+        to any existing RETURNING clause, excluding one that is specified
+        by the :meth:`.UpdateBase.returning` method.   The column values
+        will then be available on the result using the
+        :meth:`.ResultProxy.server_returned_defaults` method as a
+        dictionary, referring to values keyed to the :meth:`.Column` object
+        as well as its ``.key``.
+
+        This method differs from :meth:`.UpdateBase.returning` in these ways:
+
+        1. It is compatible with any backend.  Backends that don't support
+           RETURNING will skip the usage of the feature, rather than raising
+           an exception.  The return value of :attr:`.ResultProxy.returned_defaults`
+           will be ``None``
+
+        2. It is compatible with the existing logic to fetch auto-generated
+           primary key values, also known as "implicit returning".  Backends that
+           support RETURNING will automatically make use of RETURNING in order
+           to fetch the value of newly generated primary keys; while the
+           :meth:`.UpdateBase.returning` method circumvents this behavior,
+           :meth:`.UpdateBase.return_defaults` leaves it intact.
+
+        3. :meth:`.UpdateBase.returning` leaves the cursor's rows ready for
+           fetching using methods like :meth:`.ResultProxy.fetchone`, whereas
+           :meth:`.ValuesBase.return_defaults` fetches the row internally.
+           While all DBAPI backends observed so far seem to only support
+           RETURNING with single-row executions,
+           technically :meth:`.UpdateBase.returning` would support a backend
+           that can deliver multiple RETURNING rows as well.  However
+           :meth:`.ValuesBase.return_defaults` is single-row by definition.
+
+        :param cols: optional list of column key names or :class:`.Column`
+         objects.  If omitted, all column expressions evaulated on the server
+         are added to the returning list.
+
+        .. versionadded:: 0.9.0
+
+        .. seealso::
+
+            :meth:`.UpdateBase.returning`
+
+            :meth:`.ResultProxy.returned_defaults`
+
+        """
+        self._return_defaults = cols or True
+
 
 class Insert(ValuesBase):
     """Represent an INSERT construct.
@@ -326,52 +383,15 @@ class Insert(ValuesBase):
                 bind=None,
                 prefixes=None,
                 returning=None,
+                return_defaults=False,
                 **kwargs):
-        """Construct an :class:`.Insert` object.
-
-        Similar functionality is available via the
-        :meth:`~.TableClause.insert` method on
-        :class:`~.schema.Table`.
-
-        :param table: :class:`.TableClause` which is the subject of the insert.
-
-        :param values: collection of values to be inserted; see
-         :meth:`.Insert.values` for a description of allowed formats here.
-         Can be omitted entirely; a :class:`.Insert` construct will also
-         dynamically render the VALUES clause at execution time based on
-         the parameters passed to :meth:`.Connection.execute`.
-
-        :param inline: if True, SQL defaults will be compiled 'inline' into the
-          statement and not pre-executed.
-
-        If both `values` and compile-time bind parameters are present, the
-        compile-time bind parameters override the information specified
-        within `values` on a per-key basis.
-
-        The keys within `values` can be either :class:`~sqlalchemy.schema.Column`
-        objects or their string identifiers. Each key may reference one of:
-
-        * a literal data value (i.e. string, number, etc.);
-        * a Column object;
-        * a SELECT statement.
-
-        If a ``SELECT`` statement is specified which references this
-        ``INSERT`` statement's table, the statement will be correlated
-        against the ``INSERT`` statement.
-
-        .. seealso::
-
-            :ref:`coretutorial_insert_expressions` - SQL Expression Tutorial
-
-            :ref:`inserts_and_updates` - SQL Expression Tutorial
-
-        """
         ValuesBase.__init__(self, table, values, prefixes)
         self._bind = bind
         self.select = None
         self.inline = inline
         self._returning = returning
         self.kwargs = kwargs
+        self._return_defaults = return_defaults
 
     def get_children(self, **kwargs):
         if self.select is not None:
@@ -446,109 +466,8 @@ class Update(ValuesBase):
                 bind=None,
                 prefixes=None,
                 returning=None,
+                return_defaults=False,
                 **kwargs):
-        """Construct an :class:`.Update` object.
-
-        E.g.::
-
-            from sqlalchemy import update
-
-            stmt = update(users).where(users.c.id==5).\\
-                    values(name='user #5')
-
-        Similar functionality is available via the
-        :meth:`~.TableClause.update` method on
-        :class:`.Table`::
-
-            stmt = users.update().\\
-                        where(users.c.id==5).\\
-                        values(name='user #5')
-
-        :param table: A :class:`.Table` object representing the database
-         table to be updated.
-
-        :param whereclause: Optional SQL expression describing the ``WHERE``
-         condition of the ``UPDATE`` statement.   Modern applications
-         may prefer to use the generative :meth:`~Update.where()`
-         method to specify the ``WHERE`` clause.
-
-         The WHERE clause can refer to multiple tables.
-         For databases which support this, an ``UPDATE FROM`` clause will
-         be generated, or on MySQL, a multi-table update.  The statement
-         will fail on databases that don't have support for multi-table
-         update statements.  A SQL-standard method of referring to
-         additional tables in the WHERE clause is to use a correlated
-         subquery::
-
-            users.update().values(name='ed').where(
-                    users.c.name==select([addresses.c.email_address]).\\
-                                where(addresses.c.user_id==users.c.id).\\
-                                as_scalar()
-                    )
-
-         .. versionchanged:: 0.7.4
-             The WHERE clause can refer to multiple tables.
-
-        :param values:
-          Optional dictionary which specifies the ``SET`` conditions of the
-          ``UPDATE``.  If left as ``None``, the ``SET``
-          conditions are determined from those parameters passed to the
-          statement during the execution and/or compilation of the
-          statement.   When compiled standalone without any parameters,
-          the ``SET`` clause generates for all columns.
-
-          Modern applications may prefer to use the generative
-          :meth:`.Update.values` method to set the values of the
-          UPDATE statement.
-
-        :param inline:
-          if True, SQL defaults present on :class:`.Column` objects via
-          the ``default`` keyword will be compiled 'inline' into the statement
-          and not pre-executed.  This means that their values will not
-          be available in the dictionary returned from
-          :meth:`.ResultProxy.last_updated_params`.
-
-        If both ``values`` and compile-time bind parameters are present, the
-        compile-time bind parameters override the information specified
-        within ``values`` on a per-key basis.
-
-        The keys within ``values`` can be either :class:`.Column`
-        objects or their string identifiers (specifically the "key" of the
-        :class:`.Column`, normally but not necessarily equivalent to
-        its "name").  Normally, the
-        :class:`.Column` objects used here are expected to be
-        part of the target :class:`.Table` that is the table
-        to be updated.  However when using MySQL, a multiple-table
-        UPDATE statement can refer to columns from any of
-        the tables referred to in the WHERE clause.
-
-        The values referred to in ``values`` are typically:
-
-        * a literal data value (i.e. string, number, etc.)
-        * a SQL expression, such as a related :class:`.Column`,
-          a scalar-returning :func:`.select` construct,
-          etc.
-
-        When combining :func:`.select` constructs within the values
-        clause of an :func:`.update` construct,
-        the subquery represented by the :func:`.select` should be
-        *correlated* to the parent table, that is, providing criterion
-        which links the table inside the subquery to the outer table
-        being updated::
-
-            users.update().values(
-                    name=select([addresses.c.email_address]).\\
-                            where(addresses.c.user_id==users.c.id).\\
-                            as_scalar()
-                )
-
-        .. seealso::
-
-            :ref:`inserts_and_updates` - SQL Expression
-            Language Tutorial
-
-
-        """
         ValuesBase.__init__(self, table, values, prefixes)
         self._bind = bind
         self._returning = returning
@@ -558,6 +477,7 @@ class Update(ValuesBase):
             self._whereclause = None
         self.inline = inline
         self.kwargs = kwargs
+        self._return_defaults = return_defaults
 
 
     def get_children(self, **kwargs):
diff --git a/lib/sqlalchemy/sql/expression.py b/lib/sqlalchemy/sql/expression.py
index bbbe0b235..01091bc0a 100644
--- a/lib/sqlalchemy/sql/expression.py
+++ b/lib/sqlalchemy/sql/expression.py
@@ -49,7 +49,7 @@ from .selectable import Alias, Join, Select, Selectable, TableClause, \
         subquery, HasPrefixes, Exists, ScalarSelect
 
 
-from .dml import Insert, Update, Delete
+from .dml import Insert, Update, Delete, UpdateBase, ValuesBase
 
 # factory functions - these pull class-bound constructors and classmethods
 # from SQL elements and selectables into public functions.  This allows
@@ -101,6 +101,7 @@ from .elements import _literal_as_text, _clause_element_as_expr,\
 from .selectable import _interpret_as_from
 
 
+
 # old names for compatibility
 _Executable = Executable
 _BindParamClause = BindParameter