Google App Engine: how to tell sort location for a user value?

开发者_如何学CIn my Main model I have a total_value and I sort with this value. When a user enters a value I wish to tell the user the order of his total_value. How do I do this?

In other words, if total_values in database are 5,8,10,25 and a user enters a total_value of 15 how do I tell him that he will be in the 4th place?

Thanks!

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You need to write a query which counts the number of values smaller than the user's total_value. This may be slow if there are many Main entities. In that case, you may wish to only count the first N values smaller, and then stop (e.g., tell the user they are ranked 1000+). Your query might look like this:

# get the rank of total_value compared to existing total_values (up to 1,000)
rank = Main.all().filter('total_value <', total_value).count(1000) + 1

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The count-based solutions David and Rahul propose will only work efficiently for small numbers of entities. If you want to determine position inside a large list, you want something like the ranklist project.

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You could get the count of number of entities that have total_value less than or equal to the current users total_value.

You could use the count() method to do so (on a Query object).