Fixed #2800: the ifchanged tag now can optionally take paramaters to be checked for changing (instead of always using the content). Thanks, Wolfram Kriesing.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@4050 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/template/defaulttags.py

@@ -124,17 +124,27 @@ class ForNode(Node):
         return nodelist.render(context)
 
 class IfChangedNode(Node):
-    def __init__(self, nodelist):
+    def __init__(self, nodelist, *varlist):
         self.nodelist = nodelist
         self._last_seen = None
+        self._varlist = varlist
 
     def render(self, context):
         if context.has_key('forloop') and context['forloop']['first']:
             self._last_seen = None
-        content = self.nodelist.render(context)
-        if content != self._last_seen:
+        try:
+            if self._varlist:
+                # Consider multiple parameters.
+                # This automatically behaves like a OR evaluation of the multiple variables.
+                compare_to = [resolve_variable(var, context) for var in self._varlist]
+            else:
+                compare_to = self.nodelist.render(context)
+        except VariableDoesNotExist:
+            compare_to = None        
+
+        if  compare_to != self._last_seen:
             firstloop = (self._last_seen == None)
-            self._last_seen = content
+            self._last_seen = compare_to
             context.push()
             context['ifchanged'] = {'firstloop': firstloop}
             content = self.nodelist.render(context)
@@ -634,9 +644,11 @@ def ifchanged(parser, token):
     """
     Check if a value has changed from the last iteration of a loop.
 
-    The 'ifchanged' block tag is used within a loop. It checks its own rendered
-    contents against its previous state and only displays its content if the
-    value has changed::
+    The 'ifchanged' block tag is used within a loop. It has two possible uses.
+
+    1. Checks its own rendered contents against its previous state and only
+       displays the content if it has changed. For example, this displays a list of
+       days, only displaying the month if it changes::
 
             <h1>Archive for {{ year }}</h1>
 
@@ -644,13 +656,22 @@ def ifchanged(parser, token):
                 {% ifchanged %}<h3>{{ date|date:"F" }}</h3>{% endifchanged %}
                 <a href="{{ date|date:"M/d"|lower }}/">{{ date|date:"j" }}</a>
             {% endfor %}
+
+    2. If given a variable, check if that variable has changed. For example, the
+       following shows the date every time it changes, but only shows the hour if both
+       the hour and the date has changed::
+
+            {% for date in days %}
+                {% ifchanged date.date %} {{date.date}} {% endifchanged %}
+                {% ifchanged date.hour date.date %}
+                    {{date.hour}}
+                {% endifchanged %}
+            {% endfor %}
     """
     bits = token.contents.split()
-    if len(bits) != 1:
-        raise TemplateSyntaxError, "'ifchanged' tag takes no arguments"
     nodelist = parser.parse(('endifchanged',))
     parser.delete_first_token()
-    return IfChangedNode(nodelist)
+    return IfChangedNode(nodelist, *bits[1:])
 ifchanged = register.tag(ifchanged)
 
 #@register.tag

docs/templates.txt

@@ -525,15 +525,28 @@ ifchanged
 
 Check if a value has changed from the last iteration of a loop.
 
-The ``ifchanged`` block tag is used within a loop. It checks its own rendered
-contents against its previous state and only displays its content if the value
-has changed::
+The 'ifchanged' block tag is used within a loop. It has two possible uses.
+
+1. Checks its own rendered contents against its previous state and only
+   displays the content if it has changed. For example, this displays a list of
+   days, only displaying the month if it changes::
 
         <h1>Archive for {{ year }}</h1>
 
-    {% for day in days %}
-    {% ifchanged %}<h3>{{ day|date:"F" }}</h3>{% endifchanged %}
-    <a href="{{ day|date:"M/d"|lower }}/">{{ day|date:"j" }}</a>
+        {% for date in days %}
+            {% ifchanged %}<h3>{{ date|date:"F" }}</h3>{% endifchanged %}
+            <a href="{{ date|date:"M/d"|lower }}/">{{ date|date:"j" }}</a>
+        {% endfor %}
+        
+2. If given a variable, check if that variable has changed. For example, the
+   following shows the date every time it changes, but only shows the hour if both
+   the hour and the date has changed::
+    
+        {% for date in days %}
+            {% ifchanged date.date %} {{date.date}} {% endifchanged %}
+            {% ifchanged date.hour date.date %}
+                {{date.hour}}
+            {% endifchanged %}
         {% endfor %}
 
 ifequal

tests/regressiontests/templates/tests.py

@@ -329,6 +329,21 @@ class Templates(unittest.TestCase):
             'ifchanged06': ('{% for n in num %}{% ifchanged %}{{ n }}{% endifchanged %}{% for x in numx %}{% ifchanged %}{{ x }}{% endifchanged %}{% endfor %}{% endfor %}', { 'num': (1, 1, 1), 'numx': (2, 2, 2)}, '1222'),
             'ifchanged07': ('{% for n in num %}{% ifchanged %}{{ n }}{% endifchanged %}{% for x in numx %}{% ifchanged %}{{ x }}{% endifchanged %}{% for y in numy %}{% ifchanged %}{{ y }}{% endifchanged %}{% endfor %}{% endfor %}{% endfor %}', { 'num': (1, 1, 1), 'numx': (2, 2, 2), 'numy': (3, 3, 3)}, '1233323332333'),
             
+            # Test one parameter given to ifchanged.
+            'ifchanged-param01': ('{% for n in num %}{% ifchanged n %}..{% endifchanged %}{{ n }}{% endfor %}', { 'num': (1,2,3) }, '..1..2..3'),
+            'ifchanged-param02': ('{% for n in num %}{% for x in numx %}{% ifchanged n %}..{% endifchanged %}{{ x }}{% endfor %}{% endfor %}', { 'num': (1,2,3), 'numx': (5,6,7) }, '..567..567..567'),
+            
+            # Test multiple parameters to ifchanged.
+            'ifchanged-param03': ('{% for n in num %}{{ n }}{% for x in numx %}{% ifchanged x n %}{{ x }}{% endifchanged %}{% endfor %}{% endfor %}', { 'num': (1,1,2), 'numx': (5,6,6) }, '156156256'),
+            
+            # Test a date+hour like construct, where the hour of the last day
+            # is the same but the date had changed, so print the hour anyway.
+            'ifchanged-param04': ('{% for d in days %}{% ifchanged %}{{ d.day }}{% endifchanged %}{% for h in d.hours %}{% ifchanged d h %}{{ h }}{% endifchanged %}{% endfor %}{% endfor %}', {'days':[{'day':1, 'hours':[1,2,3]},{'day':2, 'hours':[3]},] }, '112323'),
+            
+            # Logically the same as above, just written with explicit
+            # ifchanged for the day.
+            'ifchanged-param04': ('{% for d in days %}{% ifchanged d.day %}{{ d.day }}{% endifchanged %}{% for h in d.hours %}{% ifchanged d.day h %}{{ h }}{% endifchanged %}{% endfor %}{% endfor %}', {'days':[{'day':1, 'hours':[1,2,3]},{'day':2, 'hours':[3]},] }, '112323'),
+
             ### IFEQUAL TAG ###########################################################
             'ifequal01': ("{% ifequal a b %}yes{% endifequal %}", {"a": 1, "b": 2}, ""),
             'ifequal02': ("{% ifequal a b %}yes{% endifequal %}", {"a": 1, "b": 1}, "yes"),