- add PG-specific aggregate_order_by(), references #3132

1 files changed, 63 insertions, 0 deletions

diff --git a/lib/sqlalchemy/dialects/postgresql/ext.py b/lib/sqlalchemy/dialects/postgresql/ext.py
new file mode 100644
index 000000000..57592bac2
--- /dev/null
+++ b/lib/sqlalchemy/dialects/postgresql/ext.py
@@ -0,0 +1,63 @@
+# postgresql/ext.py
+# Copyright (C) 2005-2015 the SQLAlchemy authors and contributors
+# <see AUTHORS file>
+#
+# This module is part of SQLAlchemy and is released under
+# the MIT License: http://www.opensource.org/licenses/mit-license.php
+
+from ...sql import expression
+from ...sql import elements
+
+
+class aggregate_order_by(expression.ColumnElement):
+    """Represent a Postgresql aggregate order by expression.
+
+    E.g.::
+
+        from sqlalchemy.dialects.postgresql import aggregate_order_by
+        expr = func.array_agg(aggregate_order_by(table.c.a, table.c.b.desc()))
+        stmt = select([expr])
+
+    would represent the expression::
+
+        SELECT array_agg(a ORDER BY b DESC) FROM table;
+
+    Similarly::
+
+        expr = func.string_agg(
+            table.c.a,
+            aggregate_order_by(literal_column("','"), table.c.a)
+        )
+        stmt = select([expr])
+
+    Would represent::
+
+        SELECT string_agg(a, ',' ORDER BY a) FROM table;
+
+    .. versionadded:: 1.1
+
+    .. seealso::
+
+        :class:`.array_agg`
+
+    """
+
+    __visit_name__ = 'aggregate_order_by'
+
+    def __init__(self, target, order_by):
+        self.target = elements._literal_as_binds(target)
+        self.order_by = elements._literal_as_binds(order_by)
+
+    def self_group(self, against=None):
+        return self
+
+    def get_children(self, **kwargs):
+        return self.target, self.order_by
+
+    def _copy_internals(self, clone=elements._clone, **kw):
+        self.target = clone(self.target, **kw)
+        self.order_by = clone(self.order_by, **kw)
+
+    @property
+    def _from_objects(self):
+        return self.target._from_objects + self.order_by._from_objects