Getting top N players

[Neil Ghosh]

I am using the Java version of this and need to retrieve the top N players with highest scores.

One solution is just to fetch the top N "ranker_score" entities order by the value. However this would need an index on the value attribute of "ranker_score" entity.

Using objectify

return ofy().load().type( ranker_score.class ).order( "-value" ).limit( N ).list();

is the a scalable solution or we could avoid the index by traversing the tree from the right side ? In the later case getting the player_name would be difficult.

[Bartholomew Furrow]

Your idea should work as well as anything for retrieving the top N, and you won't need an index because you're only querying for one property. Two thoughts:
- Make sure you use an ancestor query based on the root key in case you ever make a second ranker
- In Code Jam, all the ranker does for us is return the score of the Nth person. The actual information we want is in a totally separate set of objects. So if we want the top N "scoreboard_row" Entities, we just query for scoreboard rows, sorting by score descending. If we want the next N, we ask the ranker for the score of the person in Nth and then query for scoreboard rows, with score <= score(Nth), and sorting by score descending.

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