Django querysets-确保只检索一次结果

又快又脏:

def getIsland(request):
    if hasattr(request, "_cached_island"):
        return request._cached_island
    try:
        island = Island.objects.get(user=request.user) # Retrieve
    except Island.DoesNotExist:
        island = Island(user=request.user) # Doesn't exist, create default one
        island.save()
    island.update() # Run scheduled tasks
    request._cached_island = island
    return island # Return

Django有一个很好的缓存系统: http://docs.djangoproject.com/en/dev/topics/cache/

这会使函数看起来像这样:

def getIsland(request):
 island = cache.get("island_"+request.user)
 if island == None:
   try:
    island = Island.objects.get(user=request.user) # Retrieve
   except Island.DoesNotExist:
    island = Island(user=request.user) # Doesn't exist, create default one
    island.save()
   island.update() # Run scheduled tasks
   cache.set("island_"+request.user, island, 60)
 return island # Return

如果您有多个进程正在运行,或者多台计算机正在访问同一个数据库,那么您当然无法减少运行此数据库的查询数。

您可以尝试使用threadlocal存储来保存用户的全局“缓存”。例如:

class UserStorage(threading.local):
    store = {}
    def getIsland(self, request):
        user_id = request.user.pk
        island = store.get(user_id)
        if island is None:
            island, created = Island.objects.get_or_create(user = user_id)
            store[user_id] = island
        island.update()
        return island