本文概述
- JPQL高级查询示例
- JPQL过滤器
- JPQL汇总
- JPQL排序
让我们考虑具有以下记录的学生表。
文章图片
JPQL高级查询示例 在此示例中, 我们将使用基本实体类（在本例中为StudentEntity.java）, 并对它执行不同的操作。
- 在com.srcmini.jpa包下创建一个名为StudentEntity.java的实体类。
package com.srcmini.jpa;
import javax.persistence.*;
@Entity@Table(name="student")public class StudentEntity { @Id private int s_id;
private String s_name;
private int s_age;
public StudentEntity(int s_id, String s_name, int s_age) {super();
this.s_id = s_id;
this.s_name = s_name;
this.s_age = s_age;
} public StudentEntity() {super();
} public int getS_id() {return s_id;
} public void setS_id(int s_id) {this.s_id = s_id;
} public String getS_name() {return s_name;
} public void setS_name(String s_name) {this.s_name = s_name;
} public int getS_age() {return s_age;
} public void setS_age(int s_age) {this.s_age = s_age;
} }- 现在, 在Persistence.xml文件中映射实体类和其他数据库配置。
<
persistence>
<
persistence-unit name="Student_details">
<
class>
com.srcmini.jpa.StudentEntity<
/class>
<
properties>
<
property name="javax.persistence.jdbc.driver" value="http://www.srcmini.com/com.mysql.jdbc.Driver"/>
<
property name="javax.persistence.jdbc.url" value="http://www.srcmini.com/jdbc:mysql://localhost:3306/studentdata"/>
<
property name="javax.persistence.jdbc.user" value="http://www.srcmini.com/root"/>
<
property name="javax.persistence.jdbc.password" value=""/>
<
property name="eclipselink.logging.level" value="http://www.srcmini.com/SEVERE"/>
<
property name="eclipselink.ddl-generation" value="http://www.srcmini.com/create-or-extend-tables"/>
<
/properties>
<
/persistence-unit>
<
/persistence>
- 现在, 我们可以对StudentEntity.java类执行以下任何操作。
Filter.java
package com.srcmini.jpa.jpql;
import com.srcmini.jpa.StudentEntity;
import javax.persistence.*;
import java.util.*;
public class Filter { public static void main( String args[]) {EntityManagerFactory emf = Persistence.createEntityManagerFactory( "Student_details" );
EntityManager em = emf.createEntityManager();
em.getTransaction().begin( );
Query q1 = em.createQuery("Select s from StudentEntity s where s.s_age between 22 and 28");
@SuppressWarnings("unchecked")List<
StudentEntity>
l1 =(List<
StudentEntity>
)q1.getResultList();
System.out.println("Between Clause");
System.out.print("s_id");
System.out.print("\t s_name");
System.out.println("\t s_age");
for(StudentEntity s:l1){System.out.print(s.getS_id());
System.out.print("\t"+s.getS_name());
System.out.println("\t"+s.getS_age());
}Query q2 = em.createQuery("Select s from StudentEntity s where s.s_age IN(20, 22, 23)");
@SuppressWarnings("unchecked")List<
StudentEntity>
l2 =(List<
StudentEntity>
)q2.getResultList();
System.out.println("IN Clause");
System.out.print("s_id");
System.out.print("\t s_name");
System.out.println("\t s_age");
for(StudentEntity s:l2){System.out.print(s.getS_id());
System.out.print("\t"+s.getS_name());
System.out.println("\t"+s.getS_age());
}Query q3 = em.createQuery("Select s from StudentEntity s where s.s_name like '%a%'");
@SuppressWarnings("unchecked")List<
StudentEntity>
l3 =(List<
StudentEntity>
)q3.getResultList();
System.out.println("Like Clause");
System.out.print("s_id");
System.out.print("\t s_name");
System.out.println("\t s_age");
for(StudentEntity s:l3){System.out.print(s.getS_id());
System.out.print("\t"+s.getS_name());
System.out.println("\t"+s.getS_age());
}em.getTransaction().commit();
em.close();
emf.close();
}}输出：
文章图片
JPQL汇总 在这里, 我们将对表执行一些聚合操作。
Aggregate.java
package com.srcmini.jpa.jpql;
import com.srcmini.jpa.StudentEntity;
import javax.persistence.*;
import java.util.*;
public class Aggregate { public static void main( String args[]) {EntityManagerFactory emf = Persistence.createEntityManagerFactory( "Student_details" );
EntityManager em = emf.createEntityManager();
em.getTransaction().begin( );
Query q1 = em.createQuery("Select count(s) from StudentEntity s");
System.out.println("Number of Student : "+q1.getSingleResult());
Query q2 = em.createQuery("Select MAX(s.s_age) from StudentEntity s");
System.out.println("Maximum age : "+q2.getSingleResult());
Query q3 = em.createQuery("Select MIN(s.s_age) from StudentEntity s");
System.out.println("Minimum age : "+q3.getSingleResult());
em.getTransaction().commit();
em.close();
emf.close();
}}输出：
文章图片
JPQL排序 在这里, 我们将基于s_age属性对表的元素进行排序。
Sorting.java
package com.srcmini.jpa.jpql;
import com.srcmini.jpa.StudentEntity;
import javax.persistence.*;
import java.util.*;
public class Sorting { public static void main( String args[]) {EntityManagerFactory emf = Persistence.createEntityManagerFactory( "Student_details" );
EntityManager em = emf.createEntityManager();
em.getTransaction().begin( );
Query q1 = em.createQuery("Select s from StudentEntity s order by s.s_age desc");
@SuppressWarnings("unchecked")List<
StudentEntity>
l1 =(List<
StudentEntity>
)q1.getResultList();
System.out.print("s_id");
System.out.print("\t s_name");
System.out.println("\t s_age");
for(StudentEntity s:l1){System.out.print(s.getS_id());
System.out.print("\t"+s.getS_name());
System.out.println("\t"+s.getS_age());
}em.getTransaction().commit();
em.close();
emf.close();
}}【JPA JPQL高级操作】输出：
文章图片
