google-cloud-datastore

I am working with GAE and have a user table. Now I want to model friend relationships between users. I am thinking of having 3 properties user1 , user2 and request_status , but the problem is in querying to find a particular user's friends. Since GAE does not allow OR filtering, I have to merge two queries. Clearly that is very inefficient. This is just one problem with my approach. If someone could suggest a solution that lets me keep track of all friend requests as well as the friendship, then that would be very helpful. Denormalization will let you more efficiently find a user's friends

Let's say I want to display a list of books and their authors. In traditional database design, I would issue a single query to retrieve rows from the Book table as well as the related Author table, a step known as eager fetching . This is done to avoid the dreaded N+1 select problem : If the Author records were retrieved lazily, my program would have to issue a separate query for each author, possibly as many queries as there are books in the list. Does Google App Engine Datastore provide a similar mechanism, or is the N+1 select problem something that is no longer relevant on this platform? I

I`m using Google App Engine and when I remove from the datastore and I list again the results, I recover stale data. What is the problem? Here is the code I use. public void remove(long id) { EntityManager em = EMFService.get().createEntityManager(); try { Todo todo = em.find(Todo.class, id); em.remove(todo); } finally { em.close(); } } public List<Todo> getTodos(String userId) { EntityManager em = EMFService.get().createEntityManager(); Query q = em .createQuery("select t from Todo t where t.author = :userId"); q.setParameter("userId", userId); List<Todo> todos = q.getResultList(); System.out

The standard way of doing singletons in Python is class Singleton(object): _instance = None def __new__(cls, *args, **kwargs): if not cls._instance: cls._instance = super(Singleton, cls).__new__(cls, *args, **kwargs) return cls._instance However, this doesn't work on App Engine, since there are may be many servers and we would get one instance per server. So how would we do it for an app engine entity? Something like: class MySingleton(db.models): def __init__(self): all = MySingleton.all() if all.count() > 0: return all.fetch(1).get() super(MySingleton, self).__init__ (*args, **kwargs) This

I've created two MapReduce Pipelines for uploading CSVs files to create Categories and Products in bulk. Each product is gets tied to a Category through a KeyProperty. The Category and Product models are built on ndb.Model, so based on the documentation, I would think they'd be automatically cached in Memcache when retrieved from the Datastore. I've run these scripts on the server to upload 30 categories and, afterward, 3000 products. All the data appears in the Datastore as expected. However, it doesn't seem like the Product upload is using Memcache to get the Categories. When I check the