How To Avoid Lazy Initialization Issues Caused By Disabling Open Session In View Via Explicit (Default) Values

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Description: The Open-Session in View anti-pattern is activated by default in SpringBoot. Now, imagine a lazy association (e.g., @OneToMany) between two entities, Author and Book (an author has associated more books). Next, a REST controller endpoint fetches an Author without the associated Book. But, the View (more precisely, Jackson), forces the lazy loading of the associated Book as well. Since OSIV will supply the already opened Session, the proxies initializations take place successfully. The solution to avoid this performance penalty starts by disabling the OSIV. Further, explicitly initialize the un-fetched lazy associations. This way, the View will not force lazy loading.

Key points:

• disable OSIV by adding in application.properties this setting: spring.jpa.open-in-view=false
• fetch an Author entity and initialize its associated Book explicitly with (default) values (e.g., null)
• set @JsonInclude(Include.NON_EMPTY) on this entity-level to avoid rendering null or what is considered empty in the resulted JSON

NOTE: If OSIV is enabled, the developer can still initialize the un-fetched lazy associations manually as long as he does this outside of a transaction to avoid flushing. But, why is this working? Since the Session is open, why the manually initialization of the associations of a managed entity doesn't trigger the flush? The answer can be found in the documentation of OpenSessionInViewFilter which specifies that: This filter will by default not flush the Hibernate Session, with the flush mode set to FlushMode.NEVER. It assumes to be used in combination with service layer transactions that care for the flushing: The active transaction manager will temporarily change the flush mode to FlushMode.AUTO during a read-write transaction, with the flush mode reset to FlushMode.NEVER at the end of each transaction. If you intend to use this filter without transactions, consider changing the default flush mode (through the "flushMode" property).

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