惠州分享Java中的JPA查询实例_北大青鸟IT学校

为了让大家更好地理解Java中的JPA查询，惠州北大青鸟老师给大家分享Java中的JPA查询的实例，希望对大家有帮助。

实例

下面的代码来自PersonDaoImpl.java。

package cn.w3cschool.common;

import java.util.List;

import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;

import org.springframework.transaction.annotation.Transactional;

@Transactionalpublic class PersonDaoImpl {  public void test(){
   prepareData();
   List<Professor> l = em.createQuery("SELECT e FROM Professor e").getResultList();    for(Professor p:l){
     System.out.println(p);
   }
 }  
 private void prepareData(){
   Professor p = new Professor();
   p.setId(0);
   p.setName("TOM");
   
   em.persist(p);
 }
 @PersistenceContext  private EntityManager em;
}

以下代码来自Professor.java。

package cn.w3cschool.common;

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;

@Entitypublic 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());
   }

}

上面的代码生成以下结果。

以下是数据库转储。

Table Name: ADDRESS




Table Name: DEPARTMENT




Table Name: PHONE




Table Name: PROFESSOR
Row:
   Column Name: ID,
   Column Type: INTEGER:
   Column Value: 0

   Column Name: NAME,
   Column Type: VARCHAR:
   Column Value: TOM

   Column Name: SALARY,
   Column Type: BIGINT:
   Column Value: 0

   Column Name: STARTDATE,
   Column Type: DATE:
   Column Value: null

   Column Name: ADDRESS_ID,
   Column Type: INTEGER:
   Column Value: null

   Column Name: DEPARTMENT_ID,
   Column Type: INTEGER:
   Column Value: null

   Column Name: MANAGER_ID,
   Column Type: INTEGER:
   Column Value: null





Table Name: PROJECT




Table Name: PROJECT_PROFESSOR

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