Consider 2 classes: class Light(db.Model): location = db.StringProperty()
class Heavy(db.Model): location = db.StringProperty() content = db.TextProperty() image1 = db.BlobProperty() image2 = db.BLobProperty() image3 = db.BlobProperty() ..., etc., etc. ... I have 2 choices when getting information from the datastore: I can either fetch just the keys, or I can fetch the entities themselves. There isn't any way to fetch only a part of an entity (say just the location property in entities of type Heavy). Assuming this is correct, I have a couple of questions: 1) If I want to access the location property in both Light and Heavy, is it fair to assume that accessing Light will be speedier than accessing Heavy, since Heavy has to fetch all sorts of data that I don't need but that is part of the entity? 2) Would it make sense to break down Heavy into more lightweight classes for more efficient lookup? This question is probably best clarified by discussing what's happening in my actual application where I allow an Author to create several WriteUps. The WriteUps have numerous properties: a heading, a sub-heading, a lot of text and, optionally, several images, and a few more properties. When displaying the contents of a WriteUp, I need to access all these properties. But sometimes, I need to access only 1 or 2 lightweight properties; for instance, on a page summarizing the WriteUps done by an author, I need to only list the heading and sub- heading; I do not need to access the text or Blob data. But there is no way to access *just* the heading or sub-heading, right? I end up fetching ALL of the entity, whether I need all of it or not. Is this correct? Or does the datastore have some way of optimizing this? Reading the In the documentation (in the Queries and Indexes section), we are told: # The query is not executed until results are accessed. results = q.fetch(5) for p in results: print "%s %s, %d inches tall" % (p.first_name, p.last_name, p.height) When are results 'accessed', when fetch() is called, or when p.first_name, p._last_name, etc. are used? I am assuming that when fetch(5) is called, all 5 entities (assuming they exist) are fetched, and if the entities contain properties other than first_name, last_name or height, they are loaded up too. Is that correct? So now I am thinking of breaking up the WriteUps class into several classes, putting all the lightweight data that I need to access frequently in one class and all the heavy data that I rarely need to access in another and using ancestor relationships and transactions to make sure everything stays together. Does this make any sense, or I am fundamentally misunderstanding how app engine fetches data? - Shailen --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Google App Engine" group. To post to this group, send email to google-appengine@googlegroups.com To unsubscribe from this group, send email to google-appengine+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/google-appengine?hl=en -~----------~----~----~----~------~----~------~--~---
