extract() is now dialect-sensitive and supports SQLite and others.

2 files changed, 44 insertions, 2 deletions

diff --git a/lib/sqlalchemy/sql/compiler.py b/lib/sqlalchemy/sql/compiler.py
index 3a982f23c..5042959b2 100644
--- a/lib/sqlalchemy/sql/compiler.py
+++ b/lib/sqlalchemy/sql/compiler.py
@@ -108,6 +108,23 @@ FUNCTIONS = {
     functions.user: 'USER'
 }
 
+EXTRACT_MAP = {
+    'month': 'month',
+    'day': 'day',
+    'year': 'year',
+    'second': 'second',
+    'hour': 'hour',
+    'doy': 'doy',
+    'minute': 'minute',
+    'quarter': 'quarter',
+    'dow': 'dow',
+    'week': 'week',
+    'epoch': 'epoch',
+    'milliseconds': 'milliseconds',
+    'microseconds': 'microseconds',
+    'timezone_hour': 'timezone_hour',
+    'timezone_minute': 'timezone_minute'
+}
 
 class _CompileLabel(visitors.Visitable):
     """lightweight label object which acts as an expression._Label."""
@@ -133,6 +150,7 @@ class DefaultCompiler(engine.Compiled):
 
     operators = OPERATORS
     functions = FUNCTIONS
+    extract_map = EXTRACT_MAP
 
     # if we are insert/update/delete. 
     # set to true when we visit an INSERT, UPDATE or DELETE
@@ -346,6 +364,10 @@ class DefaultCompiler(engine.Compiled):
     def visit_cast(self, cast, **kwargs):
         return "CAST(%s AS %s)" % (self.process(cast.clause), self.process(cast.typeclause))
 
+    def visit_extract(self, extract, **kwargs):
+        field = self.extract_map.get(extract.field, extract.field)
+        return "EXTRACT(%s FROM %s)" % (field, self.process(extract.expr))
+
     def visit_function(self, func, result_map=None, **kwargs):
         if result_map is not None:
             result_map[func.name.lower()] = (func.name, None, func.type)
diff --git a/lib/sqlalchemy/sql/expression.py b/lib/sqlalchemy/sql/expression.py
index 5a0d5b043..56f358db8 100644
--- a/lib/sqlalchemy/sql/expression.py
+++ b/lib/sqlalchemy/sql/expression.py
@@ -484,8 +484,7 @@ def cast(clause, totype, **kwargs):
 def extract(field, expr):
     """Return the clause ``extract(field FROM expr)``."""
 
-    expr = _BinaryExpression(text(field), expr, operators.from_)
-    return func.extract(expr)
+    return _Extract(field, expr)
 
 def collate(expression, collation):
     """Return the clause ``expression COLLATE collation``."""
@@ -2313,6 +2312,27 @@ class _Cast(ColumnElement):
         return self.clause._from_objects
 
 
+class _Extract(ColumnElement):
+
+    __visit_name__ = 'extract'
+
+    def __init__(self, field, expr, **kwargs):
+        self.type = sqltypes.Integer()
+        self.field = field
+        self.expr = _literal_as_binds(expr, None)
+
+    def _copy_internals(self, clone=_clone):
+        self.field = clone(self.field)
+        self.expr = clone(self.expr)
+
+    def get_children(self, **kwargs):
+        return self.field, self.expr
+
+    @property
+    def _from_objects(self):
+        return self.expr._from_objects
+
+
 class _UnaryExpression(ColumnElement):
 
     __visit_name__ = 'unary'