CODEWITHSUNDEEP
hibernatejpajpa-2.0
Jacob
Jacob

Reputation: 14741

Hibernate query executes more than expected times

I have the below mentioned Entity relationship. When I run my application, I can see that the below query generated by Hibernate executes 13 times(1+12) where 12 is the number of rows I am displaying in front end application. Ideally it should have executed only once as I am not sure why it is getting executed 12 times. If I change my number of rows to be displayed in front end application to say 20, then query executes 21 times.

How can I resolve this issue?

Hibernate auto generated query

select employee0_.EMPLOYEE_NUMBER as EMP1_2_0_, employee0_.DEPARTMENT_CODE as  
DEPARTMENT3_2_0_, employee0_.EMPLOYEE_DEPT as EMPLOYEE4_2_0_, employee0_.DESIGNATION
as DESIGNAT5_2_0_, employee0_.EMPLOYEE_NAME as EMPLOYEE6_2_0_  from EMPLOYEES 
employee0_ where employee0_.EMPLOYEE_NUMBER=?

Entity Classes

   @Entity
   public class Project
   @ManyToOne
   @JoinColumn(name = "EMPLOYEE_NUMBER", referencedColumnName = "EMPLOYEE_NUMBER")
   private Employee requester;

   @ManyToOne
   @JoinColumn(name = "APPROVER", referencedColumnName = "EMPLOYEE_NUMBER")
   private Employee approver;
   }

   @Entity
   public class Employee {
   @OneToMany(mappedBy = "requester")
   private Set<Project> requestedProjects;

   @OneToMany(mappedBy = "approver")
   private Set<Project> approvedProjects;
   }

JSF UI Source

<p:dataTable id="dataTable" var="proj" lazy="true"
    value="#{projMB.lazyModel}" styleClass="projTableStyle"
    paginator="true" paginatorPosition="bottom" rows="12"
    rowKey="#{proj.projectId}">
    <f:facet name="header">         

    <p:column id="employeeNo" headerText="Employee Name" width="16">
    <h:outputText value="#{proj.empNumber.employeeName}" />
    </p:column>
        .....
        .....

DAOImpl class where for retrieving records

CriteriaBuilder cb = entityManager.getCriteriaBuilder();
CriteriaQuery<Project> c = cb.createQuery(Project.class);
Root<Project> emp = c.from(Project.class);
c.orderBy(cb.desc(emp.get("projectId")));
c.select(emp);

CriteriaQuery<Long> countQ = cb.createQuery(Long.class);
Root<Project> empCount = countQ.from(Project.class);
countQ.select(cb.count(empCount));

List<Predicate> criteria = new ArrayList<Predicate>();
if (projectId != null) {
ParameterExpression<String> pexp = cb.parameter(String.class,
 "projectId");
Predicate predicate = cb.equal(emp.get(Project_.projectId), pexp);
criteria.add(predicate);
            }

TypedQuery<Project> q =  entityManager.createQuery(c);

Controller class

private List<Project> project = new ArrayList<Project>();
project = myservice.getDAOValues();
....

The table displays the following

Employee No, Employee Name, Project Id, Project Start Date

Edit 2

@ManyToOne
@JoinColumn(name = "REQUESTOR", referencedColumnName = "EMPLOYEE_NUMBER", 
insertable = false, updatable = false)
private RequesterDepartment requesterDepartment;

Upvotes: 2

Views: 1437

Answers (1)

JB Nizet
JB Nizet

Reputation: 692221

You want to load projects, and their respective requester or approver in a single query. This is done using a fetch join. In JPQL:

select p from Project p
left join fetch p.requester
where ...

And in Criteria, there is an equivalent construct:

Root<Project> project = c.from(Project.class);
project.fetch(Project_.requester, JoinType.LEFT);

Note that I renamed emp to project: emp would be an almost acceptable name for an Employee path. Using it for a Project path is extremely confusing.

Upvotes: 1

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