How To Avoid Lazy Initialization Issues Caused By Disabling Open Session In View Via Hibernate5Module

Note: Hibernate5Module is an add-on module for Jackson JSON processor which handles Hibernate datatypes; and specifically aspects of lazy-loading.

Description: By default, in Spring Boot, the Open Session in View anti-pattern is enabled. Now, imagine a lazy relationship (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 Proxy initializations take place successfully.

Of course, the correct decision is to disable OSIV by setting it to false, but this will not stop Jackson to try to force the lazy initialization of the associated Book entities. Running the code again will result in an exception of type: Could not write JSON: failed to lazily initialize a collection of role: com.bookstore.entity.Author.books, could not initialize proxy - no Session; nested exception is com.fasterxml.jackson.databind.JsonMappingException: failed to lazily initialize a collection of role: com.bookstore.entity.Author.books, could not initialize proxy - no Session.

Well, among the Hibernate5Module features we have support for dealing with this aspect of lazy loading and eliminate this exception. Even if OSIV will continue to be enabled (not recommended), Jackson will not use the Session opened via OSIV.

Key points:

• for Maven, add the Hibernate5Module dependency in pom.xml
• add a @Bean that returns an instance of Hibernate5Module
• annotate the Author bean with @JsonInclude(Include.NON_EMPTY) to exclude null or what is considered empty from the returned JSON

Note: The presence of Hibernate5Module instructs Jackson to initialize the lazy associations with default values (e.g., a lazy associated collection will be initialized with null). Hibernate5Module doesn't work for lazy loaded attributes. For such case consider this item.

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