Merge pull request #6 from agonzalezro/non-existent-instances

Create non-existent instances

cache_toolbox/core.py

@@ -13,7 +13,11 @@
 
 from . import app_settings
 
-def get_instance(model, instance_or_pk, timeout=None, using=None):
+
+def get_instance(
+    model, instance_or_pk,
+    timeout=None, using=None, create=False, defaults=None
+):
     """
     Returns the ``model`` instance with a primary key of ``instance_or_pk``.
 
@@ -23,6 +27,9 @@ def get_instance(model, instance_or_pk, timeout=None, using=None):
     If omitted, the timeout value defaults to
     ``settings.CACHE_TOOLBOX_DEFAULT_TIMEOUT`` instead of 0 (zero).
 
+    If ``create`` is True, we are going to create the instance in case that it
+    was not found.
+
     Example::
 
         >>> get_instance(User, 1) # Cache miss
@@ -58,7 +65,12 @@ def get_instance(model, instance_or_pk, timeout=None, using=None):
             cache.delete(key)
 
     # Use the default manager so we are never filtered by a .get_query_set()
-    instance = model._default_manager.using(using).get(pk=pk)
+    queryset = model._default_manager.using(using)
+    if create:
+        # It's possible that the related object didn't exist yet
+        instance, _ = queryset.get_or_create(pk=pk, defaults=defaults or {})
+    else:
+        instance = queryset.get(pk=pk)
 
     data = {}
     for field in instance._meta.fields:
@@ -82,13 +94,15 @@ def get_instance(model, instance_or_pk, timeout=None, using=None):
 
     return instance
 
+
 def delete_instance(model, *instance_or_pk):
     """
     Purges the cache keys for the instances of this model.
     """
 
     cache.delete_many([instance_key(model, x) for x in instance_or_pk])
 
+
 def instance_key(model, instance_or_pk):
     """
     Returns the cache key for this (model, instance) pair.

cache_toolbox/relation.py

@@ -22,10 +22,16 @@ class Foo(models.Model):
 
         name = models.CharField(max_length=20)
 
-    cache_relation(User.foo)
+    cache_relation(User.foo, create=True, defaults={})
 
 (``primary_key`` being ``True`` is currently required.)
 
+With ``create=True`` we force the creation of an instance of `Foo` in case that
+we are trying to access to user.foo_cache but ``user.foo`` doesn't exist yet.
+
+If ``create=True`` we are going to pass the default to the get_or_create
+function.
+
 ::
 
     >>> user = User.objects.get(pk=1)
@@ -76,7 +82,8 @@ class Foo(models.Model):
 
 from .core import get_instance, delete_instance
 
-def cache_relation(descriptor, timeout=None):
+
+def cache_relation(descriptor, timeout=None, create=False, defaults=None):
     rel = descriptor.related
     related_name = '%s_cache' % rel.field.related_query_name()
 
@@ -94,7 +101,9 @@ def get(self):
         except AttributeError:
             pass
 
-        instance = get_instance(rel.model, self.pk, timeout)
+        instance = get_instance(
+            rel.model, self.pk, timeout, create=create, defaults=defaults
+        )
 
         setattr(self, '_%s_cache' % related_name, instance)