- The :func:`~.expression.column` and :func:`~.expression.table`

constructs are now importable from the "from sqlalchemy" namespace,
just like every other Core construct.
- The implicit conversion of strings to :func:`.text` constructs
when passed to most builder methods of :func:`.select` as
well as :class:`.Query` now emits a warning with just the
plain string sent.   The textual conversion still proceeds normally,
however.  The only method that accepts a string without a warning
are the "label reference" methods like order_by(), group_by();
these functions will now at compile time attempt to resolve a single
string argument to a column or label expression present in the
selectable; if none is located, the expression still renders, but
you get the warning again. The rationale here is that the implicit
conversion from string to text is more unexpected than not these days,
and it is better that the user send more direction to the Core / ORM
when passing a raw string as to what direction should be taken.
Core/ORM tutorials have been updated to go more in depth as to how text
is handled.
fixes #2992

1 files changed, 24 insertions, 4 deletions

diff --git a/lib/sqlalchemy/sql/compiler.py b/lib/sqlalchemy/sql/compiler.py
index fac4980b0..e4597dcd8 100644
--- a/lib/sqlalchemy/sql/compiler.py
+++ b/lib/sqlalchemy/sql/compiler.py
@@ -494,6 +494,22 @@ class SQLCompiler(Compiled):
     def visit_grouping(self, grouping, asfrom=False, **kwargs):
         return "(" + grouping.element._compiler_dispatch(self, **kwargs) + ")"
 
+    def visit_label_reference(self, element, **kwargs):
+        selectable = self.stack[-1]['selectable']
+        try:
+            col = selectable._inner_column_dict[element.text]
+        except KeyError:
+            # treat it like text()
+            util.warn_limited(
+                "Can't resolve label reference %r; converting to text()",
+                util.ellipses_string(element.text))
+            return self.process(
+                elements.TextClause._create_text(element.text)
+            )
+        else:
+            kwargs['render_label_as_label'] = col
+            return self.process(col, **kwargs)
+
     def visit_label(self, label,
                     add_to_result_map=None,
                     within_label_clause=False,
@@ -761,7 +777,8 @@ class SQLCompiler(Compiled):
             {
                 'correlate_froms': entry['correlate_froms'],
                 'iswrapper': toplevel,
-                'asfrom_froms': entry['asfrom_froms']
+                'asfrom_froms': entry['asfrom_froms'],
+                'selectable': cs
             })
 
         keyword = self.compound_keywords.get(cs.keyword)
@@ -1480,7 +1497,8 @@ class SQLCompiler(Compiled):
         new_entry = {
             'asfrom_froms': new_correlate_froms,
             'iswrapper': iswrapper,
-            'correlate_froms': all_correlate_froms
+            'correlate_froms': all_correlate_froms,
+            'selectable': select,
         }
         self.stack.append(new_entry)
 
@@ -1791,7 +1809,8 @@ class SQLCompiler(Compiled):
         self.stack.append(
             {'correlate_froms': set([update_stmt.table]),
              "iswrapper": False,
-             "asfrom_froms": set([update_stmt.table])})
+             "asfrom_froms": set([update_stmt.table]),
+             "selectable": update_stmt})
 
         self.isupdate = True
 
@@ -2247,7 +2266,8 @@ class SQLCompiler(Compiled):
     def visit_delete(self, delete_stmt, **kw):
         self.stack.append({'correlate_froms': set([delete_stmt.table]),
                            "iswrapper": False,
-                           "asfrom_froms": set([delete_stmt.table])})
+                           "asfrom_froms": set([delete_stmt.table]),
+                           "selectable": delete_stmt})
         self.isdelete = True
 
         text = "DELETE "