Fixed #20945 -- Allowed cache tag to use a specific cache.

django/templatetags/cache.py

 from __future__ import unicode_literals
 
+from django.core.cache import get_cache, InvalidCacheBackendError
 from django.core.cache.utils import make_template_fragment_key
 from django.template import Library, Node, TemplateSyntaxError, VariableDoesNotExist
-from django.core.cache import cache
 
 register = Library()
 
+try:
+    default_cache = get_cache('template_fragments')
+except InvalidCacheBackendError:
+    from django.core.cache import cache as default_cache
+
+
 class CacheNode(Node):
-    def __init__(self, nodelist, expire_time_var, fragment_name, vary_on):
+    def __init__(self, nodelist, expire_time_var, fragment_name, vary_on, cache_name):
         self.nodelist = nodelist
         self.expire_time_var = expire_time_var
         self.fragment_name = fragment_name
         self.vary_on = vary_on
+        self.cache_name = cache_name
 
     def render(self, context):
         try:
@@ -22,6 +29,17 @@ class CacheNode(Node):
             expire_time = int(expire_time)
         except (ValueError, TypeError):
             raise TemplateSyntaxError('"cache" tag got a non-integer timeout value: %r' % expire_time)
+        if self.cache_name:
+            try:
+                cache_name = self.cache_name.resolve(context)
+            except VariableDoesNotExist:
+                raise TemplateSyntaxError('"cache" tag got an unknown variable: %r' % self.cache_name.var)
+            try:
+                cache = get_cache(cache_name)
+            except InvalidCacheBackendError:
+                raise TemplateSyntaxError('Invalid cache name specified for cache tag: %r' % cache_name)
+        else:
+            cache = default_cache
         vary_on = [var.resolve(context) for var in self.vary_on]
         cache_key = make_template_fragment_key(self.fragment_name, vary_on)
         value = cache.get(cache_key)
@@ -50,6 +68,9 @@ def do_cache(parser, token):
             .. some expensive processing ..
         {% endcache %}
 
+    Optionally the cache to use may be specified thus::
+
+        {% cache ....  using="cachename" %}
     Each unique set of arguments will result in a unique cache entry.
     """
     nodelist = parser.parse(('endcache',))
@@ -57,7 +78,14 @@ def do_cache(parser, token):
     tokens = token.split_contents()
     if len(tokens) < 3:
         raise TemplateSyntaxError("'%r' tag requires at least 2 arguments." % tokens[0])
+    if len(tokens) > 3 and tokens[-1].startswith('using='):
+        cache_name = parser.compile_filter(tokens[-1][len('using='):])
+        tokens = tokens[:-1]
+    else:
+        cache_name = None
     return CacheNode(nodelist,
         parser.compile_filter(tokens[1]),
         tokens[2], # fragment_name can't be a variable.
-        [parser.compile_filter(t) for t in tokens[3:]])
+        [parser.compile_filter(t) for t in tokens[3:]],
+        cache_name,
+    )

docs/releases/1.7.txt

@@ -396,6 +396,11 @@ Templates
   <naive_vs_aware_datetimes>` ``datetime`` instances performing the expected
   rendering.
 
+* The :ttag:`cache` tag will now try to use the cache called
+  "template_fragments" if it exists and fall back to using the default cache
+  otherwise. It also now accepts an optional ``using`` keyword argument to
+  control which cache it uses.
+
 Requests
 ^^^^^^^^
 

docs/topics/cache.txt

@@ -652,6 +652,19 @@ equivalent:
 This feature is useful in avoiding repetition in templates. You can set the
 timeout in a variable, in one place, and just reuse that value.
 
+.. versionadded:: 1.7
+
+    By default, the cache tag will try to use the cache called
+    "template_fragments". If no such cache exists, it will fall back to using
+    the default cache. You may select an alternate cache backend to use with
+    the ``using`` keyword argument, which must be the last argument to the tag.
+
+.. code-block:: html+django
+
+    {% cache 300 local-thing ...  using="localcache" %}
+
+It is considered an error to specify a cache name that is not configured.
+
 .. function:: django.core.cache.utils.make_template_fragment_key(fragment_name, vary_on=None)
 
 If you want to obtain the cache key used for a cached fragment, you can use

tests/template_tests/tests.py

@@ -478,6 +478,42 @@ class TemplateRegressionTests(TestCase):
         cachenode = t.nodelist[1]
         self.assertEqual(cachenode.fragment_name, 'regression_20130')
 
+    @override_settings(CACHES={
+        'default': {
+            'BACKEND': 'django.core.cache.backends.locmem.LocMemCache',
+            'LOCATION': 'default',
+        },
+        'template_fragments': {
+            'BACKEND': 'django.core.cache.backends.locmem.LocMemCache',
+            'LOCATION': 'fragments',
+        },
+    })
+    def test_cache_fragment_cache(self):
+        """
+        When a cache called "template_fragments" is present, the cache tag
+        will use it in preference to 'default'
+        """
+        t1 = Template('{% load cache %}{% cache 1 fragment %}foo{% endcache %}')
+        t2 = Template('{% load cache %}{% cache 1 fragment using="default" %}bar{% endcache %}')
+
+        ctx = Context()
+        o1 = t1.render(ctx)
+        o2 = t2.render(ctx)
+
+        self.assertEqual(o1, 'foo')
+        self.assertNotEqual(o1, o2)
+
+    def test_cache_missing_backend(self):
+        """
+        When a cache that doesn't exist is specified, the cache tag will
+        raise a TemplateSyntaxError
+        '"""
+        t = Template('{% load cache %}{% cache 1 backend using="unknown" %}bar{% endcache %}')
+
+        ctx = Context()
+        with self.assertRaises(TemplateSyntaxError):
+            t.render(ctx)
+
     def test_ifchanged_render_once(self):
         """ Test for ticket #19890. The content of ifchanged template tag was
         rendered twice."""
@@ -1736,7 +1772,6 @@ class TemplateTests(TransRealMixin, TestCase):
             # Test whitespace in filter arguments
             'cache18': ('{% load cache custom %}{% cache 2|noop:"x y" cache18 %}cache18{% endcache %}', {}, 'cache18'),
 
-
             ### AUTOESCAPE TAG ##############################################
             'autoescape-tag01': ("{% autoescape off %}hello{% endautoescape %}", {}, "hello"),
             'autoescape-tag02': ("{% autoescape off %}{{ first }}{% endautoescape %}", {"first": "<b>hello</b>"}, "<b>hello</b>"),