- The type/expression system now does a more complete job

of determining the return type from an expression
as well as the adaptation of the Python operator into
a SQL operator, based on the full left/right/operator
of the given expression.  In particular
the date/time/interval system created for Postgresql
EXTRACT in [ticket:1647] has now been generalized into
the type system.   The previous behavior which often
occured of an expression "column + literal" forcing
the type of "literal" to be the same as that of "column"
will now usually not occur - the type of
"literal" is first derived from the Python type of the
literal, assuming standard native Python types + date
types, before falling back to that of the known type
on the other side of the expression.  Also part
of [ticket:1683].

1 files changed, 10 insertions, 3 deletions

diff --git a/lib/sqlalchemy/dialects/postgresql/base.py b/lib/sqlalchemy/dialects/postgresql/base.py
index cfbef69e8..7d4cbbbd8 100644
--- a/lib/sqlalchemy/dialects/postgresql/base.py
+++ b/lib/sqlalchemy/dialects/postgresql/base.py
@@ -349,9 +349,16 @@ class PGCompiler(compiler.SQLCompiler):
 
     def visit_extract(self, extract, **kwargs):
         field = self.extract_map.get(extract.field, extract.field)
-        affinity = sql_util.determine_date_affinity(extract.expr)
-
-        casts = {sqltypes.Date:'date', sqltypes.DateTime:'timestamp', sqltypes.Interval:'interval', sqltypes.Time:'time'}
+        if extract.expr.type:
+            affinity = extract.expr.type._type_affinity
+        else:
+            affinity = None
+        
+        casts = {
+                    sqltypes.Date:'date', 
+                    sqltypes.DateTime:'timestamp', 
+                    sqltypes.Interval:'interval', sqltypes.Time:'time'
+                }
         cast = casts.get(affinity, None)
         if isinstance(extract.expr, sql.ColumnElement) and cast is not None:
             expr = extract.expr.op('::')(sql.literal_column(cast))