Programming Google App Engine with Java by Sanderson Dan

Author:Sanderson, Dan
Language: eng
Format: epub, mobi
Publisher: O'Reilly Media
Published: 2015-06-29T16:00:00+00:00

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Most queries that use an ancestor filter need custom indexes. There is one unusual exception: a query does not need a custom index if the query also contains equality filters on properties (and no inequality filters or sort orders). In this exceptional case, the “merge join” algorithm can use a built-in index of keys along with the built-in property indexes. In cases where the query would need a custom index anyway, the query can match the ancestor to the keys in the custom index.

In Java, you create an ancestor query by passing the ancestor key to the Query constructor:

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