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CHAPTER 13 Optimizing fetching and caching Proxies and collection wrappers can only be used to lazy load entity associations and collections. They can t be used to lazy load individual scalar properties or components. We consider this kind of optimization to be rarely useful. For example, you usually don t want to lazy load the initialPrice of an Item. Optimizing at the level of individual columns that are selected in SQL is unnecessary if you aren t working with (a) a significant number of optional columns or (b) with optional columns containing large values that have to be retrieved on-demand. Large values are best represented with locator objects (LOBs); they provide lazy loading by definition without the need for interception. However, interception (in addition to proxies, usually) can help you to optimize column reads. Let s discuss interception for lazy loading with a few examples. Imagine that you don t want to utilize a proxy of User entity class, but you still want the benefit of lazy loading an association to User for example, as seller of an Item. You map the association with no-proxy: … … The default of the lazy attribute is proxy. By setting no-proxy, you re telling Hibernate to apply interception to this association: Item item = (Item) session.get(Item.class, new Long(123)); User seller = item.getSeller(); The first line retrieves an Item object into persistent state. The second line accesses the seller of that Item. This call to getSeller() is intercepted by Hibernate and triggers the loading of the User in question. Note how proxies are more lazy than interception: You can call item.getSeller().getId() without forcing initialization of the proxy. This makes interception less useful if you only want to set references, as we discussed earlier. You can also lazy load properties that are mapped with
or ; here the attribute that enables interception is lazy=”true”, in Hibernate XML mappings. With annotations, @Basic(fetch = FetchType.LAZY) is a hint
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