what is the difference in specifying lazy = "true"
and using fetch = "select" or "join"
? which one is preferred over the other ?
regards jayendra
FetchType. LAZY = This does not load the relationships unless you invoke it via the getter method. FetchType. EAGER = This loads all the relationships.
The FetchType defines when Hibernate gets the related entities from the database, and it is one of the crucial elements for a fast persistence tier. In general, you want to fetch the entities you use in your business tier as efficiently as possible.
Difference Between EAGER and LAZY Okay, so we talked about the fact that FetchType. LAZY is the default fetch type for all Hibernate annotation relationships. We also talked about the fact that when you use the Lazy fetch type, Hibernate won't load the relationships for that particular object instance.
In general, FetchMode defines how Hibernate will fetch the data (by select, join or subselect). FetchType, on the other hand, defines whether Hibernate will load data eagerly or lazily. if the code doesn't set FetchMode, the default one is JOIN and FetchType works as defined with FetchMode.JOIN set, FetchType is ignored and a query is always eager
Which FetchMode to use depends heavily on the application, environment and typical usage. The following guideline should be seen as a rough indication of where to start. Try to play with the setting to see what works best in your application / environment: Use this when you want a quick response time when working on a single entity.
We have also specified batch-size as 10 which is required in Batch fetch mode. ... @OneToMany ( fetch = FetchType. LAZY, mappedBy = "customers") @Cascade ( CascadeType. ALL) @Fetch ( FetchMode.
If there are some use cases which only work on Order entities (which is most likely the case), you should use FetchType.LAZY in your entity mapping and use one of these options to initialize the relationship when you need them.
Let's say we have entities like this:
@Entity @Table public class Parent { @Id private Long id; @OneToMany(mappedBy="parent", fetch = FetchType.EAGER) @Fetch(FetchMode.JOIN) private List<Child> child; //getter setters } @Entity @Table public class Child { @Id private Long id; @ManyToOne(fetch = FetchType.LAZY) private Parent parent; //getter setter }
In above example, when getting Parent
entity, hibernate will automaticly load all child
entities eagerly using join. On the other hand, when you fetch Child
, Parent
entity won't be selected unless you call it explicity in your code child.getParent()
.
FetchType (Lazy/Eager) tells whether we want entity to be loaded eagerly or lazy, when there's call in code.
FetchMode (Select/Join) tells whether we want our entitity to be loaded with additional select or in one query with join or subselect.
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