Defining the global (How to cite a web site) fetch plan @OneToOne associations default
Defining the global fetch plan @OneToOne associations default to FetchType.EAGER! This default was standardized to allow Java Persistence provider implementations without lazy loading (in practice, such a persistence provider wouldn t be very useful). We recommend that you default to the Hibernate lazy loading fetch plan by setting FetchType. LAZY in your to-one association mappings and only override it when necessary: @Entity public class Item { … @ManyToOne(fetch = FetchType.LAZY) private User seller; … } You now know how to create a fetch plan; that is, how you define what part of the persistent object network should be retrieved into memory. Before we show you how to define how these objects should be loaded and how you can optimize the SQL that will be executed, we d like to demonstrate an alternative lazy loading strategy that doesn t rely on proxies. 13.1.6 Lazy loading with interception Runtime proxy generation as provided by Hibernate is an excellent choice for transparent lazy loading. The only requirement that this implementation exposes is a package or public visible no-argument constructor in classes that must be proxied and nonfinal methods and class declarations. At runtime, Hibernate generates a subclass that acts as the proxy class; this isn t possible with a private constructor or a final entity class. On the other hand, many other persistence tools don t use runtime proxies: They use interception. We don t know of many good reasons why you d use interception instead of runtime proxy generation in Hibernate. The nonprivate constructor requirement certainly isn t a big deal. However, in two cases, you may not want to work with proxies: The only cases where runtime proxies aren t completely transparent are polymorphic associations that are tested with instanceof. Or, you may want to typecast an object but can t, because the proxy is an instance of a runtime-generated subclass. We show how to avoid this issue and how to work around the problem in chapter 7, section 7.3.1, Polymorphic many-to-one associations. Interception instead of proxies also makes these issues disappear.
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