Hibernate occurs too many queries - spring

Question

I use hibernate(with ehcache)/spring/mysql/jsf.I'am getting data from two tables in mysql.And these tables are as follows:
User
id int (primary key)
name etc.
Lesson
id int (primary key)
lesson varchar
teacher_id int (foreign key from user(id) )
and Lesson model class:
#Entity
#Table(name = "oys_lesson")
#Cache(usage = CacheConcurrencyStrategy.READ_WRITE, region = "myregion")
public class Lesson {
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
#Column(name = "id", unique = true, nullable = false)
private Integer id;
#Column(name="lesson")
private String lessonName;
#ManyToOne(cascade=CascadeType.ALL,fetch=FetchType.LAZY)
#JoinColumn(name="teacher_id",nullable=false)
private User user;
//Getters and Setters
User model Class
#Entity
#Table(name = "oys_user")
#Cache(usage = CacheConcurrencyStrategy.READ_WRITE, region = "myregion")
public class User implements Serializable {
private static final long serialVersionUID = 1L;
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
#Column(name = "id", unique = true, nullable = false)
private Integer id;
private String username;
etc....
#OneToOne(cascade = CascadeType.REMOVE)
#JoinTable(name = "oys_user_role", joinColumns = { #JoinColumn(name = "user_id", referencedColumnName = "id") }, inverseJoinColumns = { #JoinColumn(name = "role_id", referencedColumnName = "id") })
private Role role;
#OneToMany(cascade = CascadeType.ALL, fetch = FetchType.LAZY, mappedBy = "user")
private Set<Lesson> teacherLessons;
//Getters and Setters
I'm getting lesson list with this daoimpl.
public List<Lesson> getLessonList() {
// TODO Auto-generated method stub
String username = SecurityContextHolder.getContext()
.getAuthentication().getName();
Query query = openSession()
.createQuery(
"from Lesson l where l.user in (select id from User u where u.username=:username)");
query.setParameter("username", username);
// query.setCacheable(true);
List<Lesson> lessonList = query.list();
if (lessonList.size() > 0)
return lessonList;
return null;
}
This query is getting lessons of the current user.My jsf page below:
<h:form id="form">
<p:dataTable var="lesson" value="#{lessonManagedBean.lessonList}"
paginator="true" rows="10" rowKey="#{lesson.id}"
paginatorTemplate="{RowsPerPageDropdown} {FirstPageLink} {PreviousPageLink} {CurrentPageReport} {NextPageLink} {LastPageLink}"
rowsPerPageTemplate="5,10,15" selectionMode="single"
selection="#{lessonManagedBean.selectedLesson}" id="carTable" lazy="true">
<p:ajax event="rowSelect" listener="#{lessonManagedBean.onRowSelect}"
update=":form:lessonDetail" oncomplete="PF('lessonDialog').show()" />
<p:column headerText="id" sortBy="#{lesson.id}"
filterBy="#{lesson.id}">
<h:outputText value="#{lesson.id}" />
</p:column>
<p:column headerText="Lesson Name" sortBy="#{lesson.lessonName}"
filterBy="#{lesson.lessonName}">
<h:outputText value="#{lesson.lessonName}" />
</p:column>
</p:dataTable>
<p:dialog header="Ders Detayları" widgetVar="lessonDialog" showEffect="fade"
hideEffect="fade" resizable="false">
<p:outputPanel id="lessonDetail" style="text-align:center;">
<p:panelGrid columns="2"
rendered="#{not empty lessonManagedBean.selectedLesson}"
columnClasses="label,value">
<h:outputText value="Id:" />
<h:outputText value="#{lessonManagedBean.selectedLesson.id}" />
<h:outputText value="Lesson Name" />
<h:outputText value="#{lessonManagedBean.selectedLesson.lessonName}" />
</p:panelGrid>
</p:outputPanel>
</p:dialog>
</h:form>
When I opened this page,I get the following output in console.
Hibernate: select lesson0_.id as id0_, lesson0_.lesson as lesson0_, lesson0_.teacher_id as teacher3_0_ from oys_lesson lesson0_
where lesson0_.teacher_id in (select user1_.id from oys_user user1_
left outer join oys_user_role user1_1_ on user1_.id=user1_1_.user_id
where user1_.username=?)
When page opened,This query is running 3 times.3 of the same query.But when I selected row.dialog window opens and running the same query more 19 times.
managedBean.class
#ManagedBean
#SessionScoped
public class LessonManagedBean implements Serializable {
private Lesson selectedLesson=null;
List<Lesson> lessonList;
//Getters and Setters
Why is running the same query repeatedly?When the dialog window opens, do not need to run any query?Why it works 19 times?thanks in advance..

Answer 1

I solved my problem.Hibernate occurs too many queries.Because JSF calls getters multiple times.So my getList methods works multiple times.
This usually is not seen as a major problem.Because getter method is a very cheap operation.
But, if you're performing expensive business logic(db operation) in the getter method (like me),this would be re-executed everytime.So, the same query(in the getter method) works again and again.
The simplest solution:
public List<Object> getPropList(){
if(propList==null){
propList=loadListFromDb();
}
return propList;
}
For more details:
Why JSF calls getters multiple times?

Answer 2

Number of queries is dependent on FetchMode, by default it is FetchMode.SELECT, so it will fire select statements, change it to FetchMode.SUBSELECT or FetchMode.JOIN and check the queries.
#OneToMany(cascade = CascadeType.ALL, fetch = FetchType.LAZY, mappedBy = "user")
#Fetch(FetchMode.SUBSELECT)
private Set<Lesson> teacherLessons;