Aggregate function: AVG : EJB Query Language « JPA « Java






Aggregate function: AVG



File: Department.java


import java.util.HashSet;
import java.util.Set;

import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.OneToMany;

@Entity
public class Department {
    @Id
    private int id;
    private String name;
    @OneToMany(mappedBy="department")
    private Set<Professor> employees = new HashSet<Professor>();

    public int getId() {
        return id;
    }
    
    public void setId(int deptNo) {
        this.id = deptNo;
    }
    
    public String getName() {
        return name;
    }
    
    public void setName(String deptName) {
        this.name = deptName;
    }
    
    public Set<Professor> getProfessors() {
        return employees;
    }

    public String toString() {
        return "Department no: " + getId() + 
               ", name: " + getName();
    }
}


File: Phone.java



import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.OneToOne;

@Entity
public class Phone {
    @Id
    private long id;
    private String number;
    private String type;
    @OneToOne Professor employee;
    
    public long getId() {
        return id;
    }
    
    public void setId(long id) {
        this.id = id;
    }
    
    public String getNumber() {
        return number;
    }
    
    public void setNumber(String phoneNo) {
        this.number = phoneNo;
    }
    
    public String getType() {
        return type;
    }
    
    public void setType(String phoneType) {
        this.type = phoneType;
    }
    
    public Professor getProfessor() {
        return employee;
    }

    public void setProfessor(Professor employee) {
        this.employee = employee;
    }

    public String toString() {
        return "Phone id: " + getId() + 
               ", no: " + getNumber() +
               ", type: " + getType();
    }
}


File: Professor.java

import java.util.ArrayList;
import java.util.Collection;
import java.util.Date;

import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.ManyToMany;
import javax.persistence.ManyToOne;
import javax.persistence.OneToMany;
import javax.persistence.OneToOne;
import javax.persistence.Temporal;
import javax.persistence.TemporalType;

@Entity
public class Professor {
    @Id
    private int id;
    private String name;
    private long salary;
    @Temporal(TemporalType.DATE)
    private Date startDate;
    
    @OneToOne
    private Address address;
    
    @OneToMany(mappedBy="employee")
    private Collection<Phone> phones = new ArrayList<Phone>();
    
    @ManyToOne
    private Department department;
    
    @ManyToOne
    private Professor manager;
    
    @OneToMany(mappedBy="manager")
    private Collection<Professor> directs = new ArrayList<Professor>();
    
    @ManyToMany(mappedBy="employees")
    private Collection<Project> projects = new ArrayList<Project>();

    public int getId() {
        return id;
    }
    
    public void setId(int empNo) {
        this.id = empNo;
    }
    
    public String getName() {
        return name;
    }
    
    public void setName(String name) {
        this.name = name;
    }

    public long getSalary() {
        return salary;
    }

    public void setSalary(long salary) {
        this.salary = salary;
    }

    public Date getStartDate() {
        return startDate;
    }

    public void setStartDate(Date startDate) {
        this.startDate = startDate;
    }
    
    public Collection<Phone> getPhones() {
        return phones;
    }
    
    public void addPhone(Phone phone) {
        if (!getPhones().contains(phone)) {
            getPhones().add(phone);
            if (phone.getProfessor() != null) {
                phone.getProfessor().getPhones().remove(phone);
            }
            phone.setProfessor(this);
        }
    }
    
    public Department getDepartment() {
        return department;
    }
    
    public void setDepartment(Department department) {
        if (this.department != null) {
            this.department.getProfessors().remove(this);
        }
        this.department = department;
        this.department.getProfessors().add(this);
    }
    
    public Collection<Professor> getDirects() {
        return directs;
    }
    
    public void addDirect(Professor employee) {
        if (!getDirects().contains(employee)) {
            getDirects().add(employee);
            if (employee.getManager() != null) {
                employee.getManager().getDirects().remove(employee);
            }
            employee.setManager(this);
        }
    }
    
    public Professor getManager() {
        return manager;
    }
    
    public void setManager(Professor manager) {
        this.manager = manager;
    }

    public Collection<Project> getProjects() {
        return projects;
    }
    
    public void addProject(Project project) {
        if (!getProjects().contains(project)) {
            getProjects().add(project);
        }
        if (!project.getProfessors().contains(this)) {
            project.getProfessors().add(this);
        }
    }
    
    public Address getAddress() {
        return address;
    }
    
    public void setAddress(Address address) {
        this.address = address; 
    }
    
    public String toString() {
        return "Professor " + getId() + 
               ": name: " + getName() +
               ", salary: " + getSalary() +
               ", phones: " + getPhones() +
               ", managerNo: " + ((getManager() == null) ? null : getManager().getId()) +
               ", deptNo: " + ((getDepartment() == null) ? null : getDepartment().getId());
    }

}


File: ProfessorService.java

import java.util.List;

import javax.persistence.EntityManager;
import javax.persistence.Query;

public class ProfessorService {
  protected EntityManager em;

  public ProfessorService(EntityManager em) {
    this.em = em;
  }

  public List executetQuery(String queryString) {
    Query query = em.createQuery(queryString);
    return query.getResultList();
  }

  public void executeUpdate(String updateString) {
    em.createQuery(updateString).executeUpdate();
  }
}


File: Project.java



import java.util.ArrayList;
import java.util.Collection;

import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.Inheritance;
import javax.persistence.ManyToMany;

@Entity
@Inheritance
public class Project {
    @Id
    protected int id;
    protected String name;
    @ManyToMany
    protected Collection<Professor> employees = new ArrayList<Professor>();
    
    public int getId() {
        return id;
    }
    
    public void setId(int projectNo) {
        this.id = projectNo;
    }
    
    public String getName() {
        return name;
    }
    
    public void setName(String projectName) {
        this.name = projectName;
    }
    
    public Collection<Professor> getProfessors() {
        return employees;
    }
    
    public void addProfessor(Professor employee) {
        if (!getProfessors().contains(employee)) {
            getProfessors().add(employee);
        }
        if (!employee.getProjects().contains(this)) {
            employee.getProjects().add(this);
        }
    }
    
    public String toString() {
        return getClass().getName().substring(getClass().getName().lastIndexOf('.')+1) + 
                " no: " + getId() + 
                ", name: " + getName();
    }
}


File: Address.java


import javax.persistence.Entity;
import javax.persistence.Id;

@Entity
public class Address {
    @Id
    private int id;
    private String street;
    private String city;
    private String state;
    private String zip;
    
    public int getId() {
        return id;
    }
    
    public void setId(int id) {
        this.id = id;
    }
    
    public String getStreet() {
        return street;
    }
    
    public void setStreet(String address) {
        this.street = address;
    }

    public String getCity() {
        return city;
    }

    public void setCity(String city) {
        this.city = city;
    }

    public String getState() {
        return state;
    }

    public void setState(String state) {
        this.state = state;
    }

    public String getZip() {
        return zip;
    }

    public void setZip(String zip) {
        this.zip = zip;
    }
    public String toString() {
        return "Address id: " + getId() + 
               ", street: " + getStreet() +
               ", city: " + getCity() +
               ", state: " + getState() +
               ", zip: " + getZip();
    }

}


File: JPAUtil.java

import java.io.Reader;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.sql.Statement;

public class JPAUtil {
  Statement st;
  
  public JPAUtil() throws Exception{
    Class.forName("org.hsqldb.jdbcDriver");
    System.out.println("Driver Loaded.");
    String url = "jdbc:hsqldb:data/tutorial";

    Connection conn = DriverManager.getConnection(url, "sa", "");
    System.out.println("Got Connection.");
    st = conn.createStatement();
  }
  public void executeSQLCommand(String sql) throws Exception {
    st.executeUpdate(sql);
  }
  public void checkData(String sql) throws Exception {
    ResultSet rs = st.executeQuery(sql);
    ResultSetMetaData metadata = rs.getMetaData();

    for (int i = 0; i < metadata.getColumnCount(); i++) {
      System.out.print("\t"+ metadata.getColumnLabel(i + 1)); 
    }
    System.out.println("\n----------------------------------");

    while (rs.next()) {
      for (int i = 0; i < metadata.getColumnCount(); i++) {
        Object value = rs.getObject(i + 1);
        if (value == null) {
          System.out.print("\t       ");
        } else {
          System.out.print("\t"+value.toString().trim());
        }
      }
      System.out.println("");
    }
  }
}


File: Main.java

import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;

public class Main {
  public static void main(String[] a) throws Exception {
    JPAUtil util = new JPAUtil();

    EntityManagerFactory emf = Persistence.createEntityManagerFactory("ProfessorService");
    EntityManager em = emf.createEntityManager();
    ProfessorService service = new ProfessorService(em);

    em.getTransaction().begin();

    service.executetQuery("SELECT AVG(e.salary) FROM Professor e");
    
    util.checkData("select * from Professor");

    em.getTransaction().commit();
    em.close();
    emf.close();
  }
}






File: persistence.xml

<persistence xmlns="http://java.sun.com/xml/ns/persistence"
             xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
             xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence" version="1.0">
  <persistence-unit name="JPAService" transaction-type="RESOURCE_LOCAL">
    <properties>
      <property name="hibernate.dialect" value="org.hibernate.dialect.HSQLDialect"/>
      <property name="hibernate.hbm2ddl.auto" value="update"/>
      <property name="hibernate.connection.driver_class" value="org.hsqldb.jdbcDriver"/>
      <property name="hibernate.connection.username" value="sa"/>
      <property name="hibernate.connection.password" value=""/>
      <property name="hibernate.connection.url" value="jdbc:hsqldb:data/tutorial"/>
    </properties>
  </persistence-unit>
</persistence>


           
       








JPA-EJBQLUsingAVG.zip( 5,339 k)

Related examples in the same category

1.Simple Select statement
2.Select Two Entities
3.Get Two Properties From Entity
4.Get String Properties From Entities
5.Retrieve Inner Entity
6.Retrieve in One to Many Mapping
7.Reference Two Entities In Where Clause
8.Retrieve Entity Fields
9.Create Sub Query With Entities
10.Use OrderBy Clause
11.Order By Two Columns
12.Order By Descending
13.EJB QL: Having clause
14.All Operator in EJB QL
15.EJB QL: Where Clause With SubQuery
16.Using Exists clause
17.Aggregate function: Count And Avg
18.EJB QL: Concat Function With Substring
19.Use Size Function To Check Collection
20.Use In With One To One Mapping
21.Not IN
22.Not Exist With Subquery
23.Not Empty
24.Match Single Character And Multiple Characters
25.MemberOf function
26.OBJECT Funtion
27.Left Join
28.Join Two Entities in One To One Mapping
29.Join Two Entities in Many To One Mapping
30.Join Three Entities
31.Join Fetch
32.Using In function
33.Group By With Count
34.Escape wildcard
35.Entity Join With Condition
36.Empty Value
37.Distinct function
38.Count Entities
39.Count Collection
40.Conditional operator: AND
41.Between...And
42.AVG With GroupBy clause
43.Any With Subquery
44.Subquery in EJB QL