Ticket #12982: get_or_set2.diff

django/core/cache/backends/base.py

@@ -125 +125 @@
                 d[k] = val
         return d
 
+    def get_or_set(self, key, default, timeout=None, version=None):
+        """
+        Fetch a given key from the cache. If the key does not exist,
+        the default value is added to cache. If the default value is callable
+        the key will be set to return of default value.
+        Returns a tuple of (object, is_set), where is_set is a boolean
+        specifying whether the key is new in the cache
+        """
+        val, is_set = self.get(key, version=version), False
+        if val is None:
+            if callable(default):
+                val = default()
+            else:
+                val = default
+            is_set = self.add(key, val, timeout, version)
+            if not is_set:
+                val, is_set = self.get(key, version=version), False
+                if val is None:
+                    raise ValueError("get_or_set failed on Key '%s'" % key)
+        return val, is_set
+
     def has_key(self, key, version=None):
         """
         Returns True if the key is in the cache and has not expired.

docs/topics/cache.txt

@@ -744 +744 @@
 
 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. Returns a tuple of (object, is_set), where is_set is a boolean 
+specifying whether the key is new in the cache
+
+    >>> cache.get_or_set('a',1)
+    1, True
+    >>> cache.get('a')
+    1
+    >>> cache.set('b',1)
+    >>> cache.get_or_set('b',2)
+    1, False
+.. versionadded:: 1.5
+
 You can delete keys explicitly with ``delete()``. This is an easy way of
 clearing the cache for a particular object::
 

tests/regressiontests/cache/tests.py

@@ -228 +228 @@
         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
+        val, is_set = self.cache.get_or_set('a', 'a')
+        self.assertEqual(is_set, True)
+        self.assertEqual(val, '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', False))
+
+        #Test a callable
+        def cache_val():
+            return 'c'
+
+        val, is_set = self.cache.get_or_set('c', cache_val)
+        self.assertEqual(is_set, True)
+        self.assertEqual(val, 'c')
+        self.assertEqual(self.cache.get('c'), 'c')
+
     def test_delete(self):
         # Cache keys can be deleted
         self.cache.set("key1", "spam")