Lazy fetching in JPA

Lazy fetching allows the fetching of a relationship to be deferred until it is accessed. This is important not only to avoid the database access, but also to avoid the cost of building the objects if they are not needed.

In JPA lazy fetching can be set on any relationship using the fetch attribute. The fetch can be set to either LAZY or EAGER as defined in the FetchType enum. The default fetch type is LAZY for all relationships except for OneToOne and ManyToOne, but in general it is a good idea to make every relationship LAZY. The EAGER default for OneToOne and ManyToOne is for implementation reasons (more difficult to implement), not because it is a good idea. Technically in JPA LAZY is just a hint, and a JPA provider is not required to support it, however in reality all main JPA providers support it, and they would be pretty useless if they did not.


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