With Siena, what is the best way to know if an entity doesn't exist in GAE?

Question

Actually:

return all().filter("name", name).count() == 0;

May be a better way ?

Hello again, could you close this question if you read the answer? It's just not to keep false opened questions. Thanks! — mandubian, Aug 26 '11 at 10:28

plunchete · Accepted Answer · 2011-08-19T23:54:21.693

1

Regarding performance I would go for something like:

return all().filter("name", name).get() == null;

I'm not sure about GAE but in SQL a limit 1 is several times faster than count, and obviously you don't need to know how many models have this value.

edited Aug 19 '11 at 23:54

answered Aug 19 '11 at 02:00

plunchete

score 0 · Answer 2 · answered Aug 15 '11 at 20:54

Your way is not bad as you filter on a field.

If you had known the key of the entity, you could have used:

return Model.getByKey(YourClass.class, id) == null

If you want to filter on a given field, you can also use the fetch keys only :

return all().filter("name", name).fetchKeys().size() == 0;

But I wonder which is the best in term of performance. It depends on performance of GAE datastore regarding "count" or "fetch keys only" operation.

2 Answers2