Why does JPA use FetchType EAGER by default for the @ManyToOne relationship

java hibernate jpa orm hibernate-mapping
vatsal mevada picture vatsal mevada · Dec 17, 2014 · Viewed 29k times · Source

I came to notice that he default FetchType for the @ManyToOne mapping is EAGER i JPA and Hibernate, whereas, for the @OneToMany mapping, the default FetchType is LAZY.

What is the specific reason behind this?

Answer

Ankur Singhal picture Ankur Singhal · Dec 17, 2014

From the JPA 2.0 spec, the defaults are like so:

OneToMany: LAZY
ManyToOne: EAGER
ManyToMany: LAZY
OneToOne: EAGER

And in hibernate, all is Lazy

From Hibernate Docs,

By default, Hibernate uses lazy select fetching for collections and lazy proxy fetching for single-valued associations. These defaults make sense for most associations in the majority of applications.

To answer your question, Hibernate is an implementation of the JPA standard. Hibernate has its own quirks of operation, but as per the Hibernate docs

By default, Hibernate uses lazy select fetching for collections and lazy proxy fetching for single-valued associations. These defaults make sense for most associations in the majority of applications.

So Hibernate will always load any object using a lazy fetching strategy, no matter what type of relationship you have declared.

JPA Spec assumes that in general most of the applications will require the singleton relations by default be eager, whereas multi value relations by default be lazy.

Refer here for more

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