Emulating a "OR" condition in Datastore.

Question

Hello again,

I'm using the Google App Engine with Python (Django). How to emulate "SELECT * FROM bla WHERE touser = common.userstats("key") OR fromuser = common.userstats("key") ORDER BY date ASC"?

I was thinking of something like this, but I can't get it in the order I want.

    recievedlist = models.P1.all()
    recievedlist.filter("touser =", common.userstats("key"))
    plus1list = recievedlist.fetch(50)

    sendlist = models.P1.all()
    sendlist.filter("fromuser =", common.userstats("key"))
    plus1list += sendlist.fetch(50)

    # order plus1list

Answer 1

You could add a ListProperty to your model which contains both touser and fromuser. Then you could execute a single query to retrieve the entities which you are interested in sorted by date. This eliminates a datastore query and the in-memory sort, but costs you an extra index and a little more storage space on your model.

(pseudo) Example:

class bla(db.Model):
    ...
    toandfromuser = db.ListProperty(...)

Then you can do a query like this (since an entity will match if ANY element of the list toandfromuser matches the value you are looking for):

SELECT * FROM bla WHERE toandfromuser = common.userstats("key") ORDER BY date ASC