From 9573b663d5327bcb644f6776082c832ec0f49b44 Mon Sep 17 00:00:00 2001
From: Armin Ronacher <armin.ronacher@active-4.com>
Date: Tue, 21 Dec 2010 00:44:34 +0100
Subject: [PATCH] groupby now supports attributes of attributes.  This fixes
 #10

---
 CHANGES                     |  2 ++
 jinja2/compiler.py          |  2 +-
 jinja2/filters.py           | 12 +++++++++++-
 jinja2/testsuite/filters.py | 26 ++++++++++++++++++++++++++
 4 files changed, 40 insertions(+), 2 deletions(-)

diff --git a/CHANGES b/CHANGES
index b171ac2..87f705c 100644
--- a/CHANGES
+++ b/CHANGES
@@ -13,6 +13,8 @@ Version 2.6
   allows application developers to disable builtin operators for better
   security.  (For instance limit the mathematical operators to actual
   integers instead of longs)
+- groupby filter now supports dotted notation for grouping by attributes
+  of attributes.
 
 Version 2.5.5
 -------------
diff --git a/jinja2/compiler.py b/jinja2/compiler.py
index 657a8bc..a4b5a2f 100644
--- a/jinja2/compiler.py
+++ b/jinja2/compiler.py
@@ -13,7 +13,7 @@ from itertools import chain
 from copy import deepcopy
 from jinja2 import nodes
 from jinja2.nodes import EvalContext
-from jinja2.visitor import NodeVisitor, NodeTransformer
+from jinja2.visitor import NodeVisitor
 from jinja2.exceptions import TemplateAssertionError
 from jinja2.utils import Markup, concat, escape, is_python_keyword, next
 
diff --git a/jinja2/filters.py b/jinja2/filters.py
index d1848e4..3a81f70 100644
--- a/jinja2/filters.py
+++ b/jinja2/filters.py
@@ -595,8 +595,18 @@ def do_groupby(environment, value, attribute):
     As you can see the item we're grouping by is stored in the `grouper`
     attribute and the `list` contains all the objects that have this grouper
     in common.
+
+    .. versionchanged:: 2.6
+       It's now possible to use dotted notation to group by the child
+       attribute of another attribute.
     """
-    expr = lambda x: environment.getitem(x, attribute)
+    if '.' in attribute:
+        def expr(item):
+            for part in attribute.split('.'):
+                item = environment.getitem(item, part)
+            return item
+    else:
+        expr = lambda x: environment.getitem(x, attribute)
     return sorted(map(_GroupTuple, groupby(sorted(value, key=expr), expr)))
 
 
diff --git a/jinja2/testsuite/filters.py b/jinja2/testsuite/filters.py
index b59c9e3..80a6f80 100644
--- a/jinja2/testsuite/filters.py
+++ b/jinja2/testsuite/filters.py
@@ -252,6 +252,32 @@ class FilterTestCase(JinjaTestCase):
             ""
         ]
 
+    def test_groupby_multidot(self):
+        class Date(object):
+            def __init__(self, day, month, year):
+                self.day = day
+                self.month = month
+                self.year = year
+        class Article(object):
+            def __init__(self, title, *date):
+                self.date = Date(*date)
+                self.title = title
+        articles = [
+            Article('aha', 1, 1, 1970),
+            Article('interesting', 2, 1, 1970),
+            Article('really?', 3, 1, 1970),
+            Article('totally not', 1, 1, 1971)
+        ]
+        tmpl = env.from_string('''
+        {%- for year, list in articles|groupby('date.year') -%}
+            {{ year }}{% for x in list %}[{{ x.title }}]{% endfor %}|
+        {%- endfor %}''')
+        assert tmpl.render(articles=articles).split('|') == [
+            '1970[aha][interesting][really?]',
+            '1971[totally not]',
+            ''
+        ]
+
     def test_filtertag(self):
         tmpl = env.from_string("{% filter upper|replace('FOO', 'foo') %}"
                                "foobar{% endfilter %}")
-- 
2.26.2