CODEWITHSUNDEEP
pythongoogle-app-engine
John
John

Reputation: 21

SelfReferenceProperty vs. ListProperty Google App Engine

I am experimenting with the Google App Engine and have a question.

For the sake of simplicity, let's say my app is modeling a computer network (a fairly large corporate network with 10,000 nodes). I am trying to model my Node class as follows:

class Node(db.Model):
    name = db.StringProperty()
    neighbors = db.SelfReferenceProperty()

Let's suppose, for a minute, that I cannot use a ListProperty(). Based on my experiments to date, I can assign only a single entity to 'neighbors' - and I cannot use the "virtual" collection (node_set) to access the list of Node neighbors.

So... my questions are:

  1. Does SelfReferenceProperty limit you to a single entity that you can reference?
  2. If I instead use a ListProperty, I believe I am limited to 5,000 keys, which I need to exceed.

Update

All wrapped up in my shorts as I was, I forgot the *ReferenceReleationship is "backwards" --- the "list" of things points back to the one side of the relationship. The SelfReferenceProperty works as I thought it would. My bad. I'll still need to deal with the large "many" side of the relationship - and I don't think a ListProperty will do the trick, but I'll post what I find.

Thanks, John

Upvotes: 2

Views: 1013

Answers (1)

Alex Martelli
Alex Martelli

Reputation: 881675

Re 1, yes (if I understand correctly what you're asking): for each property in a model, each instance of the model (AKA "entity") has one value for that property. So e.g. an IntegerProperty has one integer value for a given entity, a SelfReferenceProperty has one value (internally a key string) for a given entity, and so forth. Not a single value for all instances of the module, of course, but I don't believe that's what you mean.

Re 2, the 5000 limit (wow, that's a lot of neighbors for a single node graph that only has 10000 nodes in all!) I believe you're referring to is on indices for an entity -- this article explains the limitation better.

One possible workaround is to have no neighbors property at all on the nodes, but rather a separate Connection model to represent the connection from one node to another (with ReferenceProperty properties, in the Connection, that each refer to a Node). You'll need something extra in the Connection (e.g., progressive counts of incoming and outgoing connections for the affected nodes) to be able to fetch many thousands of them, of course (in multiple queries, given the 1000-at-a-time limitation).

Upvotes: 1

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