support "SELECT *" for ORM queries

A :func:`_sql.select` construct that is passed a sole '*' argument for
``SELECT *``, either via string, :func:`_sql.text`, or
:func:`_sql.literal_column`, will be interpreted as a Core-level SQL
statement rather than as an ORM level statement. This is so that the ``*``,
when expanded to match any number of columns, will result in all columns
returned in the result. the ORM- level interpretation of
:func:`_sql.select` needs to know the names and types of all ORM columns up
front which can't be achieved when ``'*'`` is used.

If ``'*`` is used amongst other expressions simultaneously with an ORM
statement, an error is raised as this can't be interpreted correctly by the
ORM.

Fixes: #8235
Change-Id: Ic8e84491e14acdc8570704eadeaeaf6e16b1e870

1 files changed, 12 insertions, 0 deletions

diff --git a/lib/sqlalchemy/orm/context.py b/lib/sqlalchemy/orm/context.py
index e743eeed5..20a03e9b4 100644
--- a/lib/sqlalchemy/orm/context.py
+++ b/lib/sqlalchemy/orm/context.py
@@ -219,6 +219,7 @@ class ORMCompileState(CompileState):
             ("_set_base_alias", InternalTraversal.dp_boolean),
             ("_for_refresh_state", InternalTraversal.dp_boolean),
             ("_render_for_subquery", InternalTraversal.dp_boolean),
+            ("_is_star", InternalTraversal.dp_boolean),
         ]
 
         # set to True by default from Query._statement_20(), to indicate
@@ -241,6 +242,7 @@ class ORMCompileState(CompileState):
         _set_base_alias = False
         _for_refresh_state = False
         _render_for_subquery = False
+        _is_star = False
 
     attributes: Dict[Any, Any]
     global_attributes: Dict[Any, Any]
@@ -422,6 +424,8 @@ class ORMCompileState(CompileState):
         load_options = execution_options.get(
             "_sa_orm_load_options", QueryContext.default_load_options
         )
+        if compile_state.compile_options._is_star:
+            return result
 
         querycontext = QueryContext(
             compile_state,
@@ -1023,6 +1027,11 @@ class ORMSelectCompileState(ORMCompileState, SelectState):
 
         self._for_update_arg = query._for_update_arg
 
+        if self.compile_options._is_star and (len(self._entities) != 1):
+            raise sa_exc.CompileError(
+                "Can't generate ORM query that includes multiple expressions "
+                "at the same time as '*'; query for '*' alone if present"
+            )
         for entity in self._entities:
             entity.setup_compile_state(self)
 
@@ -2761,6 +2770,9 @@ class _RawColumnEntity(_ColumnEntity):
         self.raw_column_index = raw_column_index
         self.translate_raw_column = raw_column_index is not None
 
+        if column._is_star:
+            compile_state.compile_options += {"_is_star": True}
+
         if not is_current_entities or column._is_text_clause:
             self._label_name = None
         else: