CODEWITHSUNDEEP
google-app-enginegoogle-cloud-datastoreapp-engine-ndb
zuroc
zuroc

Reputation: 95

How can I fetch the lastest entry of a model new put into NDB?

How can I get the latest entry of a model new putted into NDB?

1: If I use a same parent key ? How to ?

I see the document write

Entities whose keys have the same root form an entity group or group. If entities are in different groups, then changes to those entities might sometimes seem to occur "out of order". If the entities are unrelated in your application's semantics, that's fine. But if some entities' changes should be consistent, your application should make them part of the same group when creating them.

Is this means , with the same parent key the order is insert order?

But , how to get the last one ?

2: If I not use a same parent key (the model is same)? How to ?

Upvotes: 0

Views: 694

Answers (1)

Jesse Rusak
Jesse Rusak

Reputation: 57188

If you're OK with eventual consistency (i.e. you might not see the very latest one immediately) you can just add a DateTimeProperty with auto_now_add=True and then run a query sorting by that property to get the latest one. (This is also approximate since you might have several entities saved close together which are ordered differently than you expect.)

If you need it to be exactly correct, the only way I can see is to create an entity whose job it is to hold a reference to the latest entry, and update that entity in the same transaction as the entry you're creating. Something like:

class LatestHolder(ndb.Model):
    latest = ndb.KeyProperty('Entry')

# code to update:

@ndb.transactional(xg=True)
def put_new_entry(entry):
    holder = LatestHolder.get_or_insert(name='fixed-key')
    holder.latest = entry
    holder.put()
    entry.put()

Note that I've used a globally fixed key name here with no parent for the holder class. This is a bottleneck; you might prefer to make several LatestHolder entities with different parents if your "latest entry" only needs to be from a particular parent, in which case you just pass a parent key to get_or_insert.

Upvotes: 4

Related Questions