Ticket #12982: get_or_set.diff

docs/topics/cache.txt

@@ -731 +731 @@
 
 Like ``cache.set()``, ``set_many()`` takes an optional ``timeout`` parameter.
 
+In cases where you may wish to use either a cached value or create a new cached value
+there is the ``get_or_set()`` method. It takes the same parameters as get but rather than simply return
+the default value, the default is set as the new cache value for that key. If the default value is callable
+it's return value will be stored.
+
+    >>> cache.get_or_set('a',1)
+    >>> cache.get('a')
+    1 
+    >>> cache.set('b',1)
+    >>> cache.get_or_set('b',2)
+    1
+
 You can delete keys explicitly with ``delete()``. This is an easy way of
 clearing the cache for a particular object::
 

django/core/cache/backends/base.py

@@ -125 +125 @@
             if val is not None:
                 d[k] = val
         return d
+    
+    def get_or_set(self,key,default,**kwargs):
+        """
+        Fetch a given key from the cache. If the key does not exist, the default value is used.
+        If the default value is callable the key will be set to it's return value.
+        """
+        val = self.get(key,**kwargs)
+        if val is None:
+            if callable(default):
+                val = default()
+            else:
+                val = default
+            self.add(key,val,**kwargs)
+        return val
+                 
 
     def has_key(self, key, version=None):
         """

tests/regressiontests/cache/tests.py

@@ -202 +202 @@
         self.assertEqual(self.cache.get_many(['a', 'c', 'd']), {'a' : 'a', 'c' : 'c', 'd' : 'd'})
         self.assertEqual(self.cache.get_many(['a', 'b', 'e']), {'a' : 'a', 'b' : 'b'})
 
+    def test_get_or_set(self):
+        #Test when no value is set
+        self.cache.get_or_set('a','a')
+        self.assertEqual(self.cache.get('a'),'a')
+
+        #Test an existing value
+        self.cache.set('b','b')
+        self.assertEqual(self.cache.get_or_set('b','c'),'b')
+
+        #Test a callable
+        def cache_val():
+            return 'c'
+
+        self.cache.get_or_set('c',cache_val)
+        self.assertEqual(self.cache.get('c'),'c')
+        
     def test_delete(self):
         # Cache keys can be deleted
         self.cache.set("key1", "spam")