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Hibernate interview questions

!!! Hibernate interview questions !!!

Q. What is lazy fetching in Hibernate? With Example .




Lazy fetching decides whether to load child objects while loading the Parent Object.
You need to do this setting respective hibernate mapping file of the parent class.
Lazy = true (means not to load child)
By default the lazy loading of the child objects is true.
This make sure that the child objects are not loaded unless they are explicitly invoked in the application by calling getChild() method on parent.In this case hibernate issues a fresh database call to load the child when getChild() is actully called on the Parent object
.But in some cases you do need to load the child objects when parent is loaded.
Just make the lazy=false and hibernate will load the child when parent is loaded from the database.
Example :
If you have a TABLE ? EMPLOYEE mapped to Employee object and contains set of Address objects.
Parent Class : Employee class
Child class : Address Class
public class Employee {
private Set address = new HashSet(); // contains set of child Address objects
public Set getAddress () {
return address;
}
public void setAddresss(Set address) {
this. address = address;
}
}
In the Employee.hbm.xml file
<set name="address" inverse="true" cascade="delete" lazy="false">
<key column="a_id" />
<one-to-many class="beans Address"/>
</set>
In the above configuration.
If lazy="false" : - when you load the Employee object that time child object Adress is also loaded and set to setAddresss() method.
If you call employee.getAdress() then loaded data returns.No fresh database call.

If lazy="true" :- This the default configuration. If you don?t mention then hibernate consider lazy=true.
when you load the Employee object that time child object Adress is not loaded. You need extra call to data base to get address objects.
If you call employee.getAdress() then that time database query fires and return results. Fresh database call.

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