Web design programs - CHAPTER 13 Optimizing fetching and caching annotation (which
CHAPTER 13 Optimizing fetching and caching annotation (which is the default in Java Persistence). Eager join fetching of single- ended associations, unlike eager outer-join fetching of collections, doesn t create a Cartesian product problem. The Cartesian product problem The opposite of the n+1 selects problem are SELECT statements that fetch too much data. This Cartesian product problem always appears if you try to fetch several parallel collections. Let s assume you ve made the decision to apply a global fetch=”join” setting to the bids collection of an Item (despite our recommendation to use global prefetching and a dynamic join-fetching strategy only when necessary). The Item class has other collections: for example, the images. Let s also assume that you decide that all images for each item have to be loaded all the time, eagerly with a fetch=”join” strategy:
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