JPA JPQL基本操作 JPAJPQL基本操作|JPA

本文概述

JPQL动态查询示例
JPQL静态查询示例

JPQL允许我们创建静态查询和动态查询。现在, 我们将使用下表中的两种查询类型执行一些基本的JPQL操作。

文章图片
JPQL动态查询示例在此示例中, 我们将使用createQuery()方法从数据库中获取单个列。
StudentEntity.java

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; } }

Persistence.xml

< 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>

FetchColumn.java

package com.srcmini.jpa.jpql; import javax.persistence.*; import java.util.*; public class FetchColumn { public static void main( String args[]) {EntityManagerFactory emf = Persistence.createEntityManagerFactory( "Student_details" ); EntityManager em = emf.createEntityManager(); em.getTransaction().begin( ); Query query = em.createQuery("Select s.s_name from StudentEntity s"); @SuppressWarnings("unchecked")List< String> list =query.getResultList(); System.out.println("Student Name :"); for(String s:list) {System.out.println(s); }em.close(); emf.close(); } }

输出：

文章图片
JPQL静态查询示例在此示例中, 我们将使用createNamedQuery()方法从数据库中获取单个列。
【JPA JPQL基本操作】StudentEntity.java

package com.srcmini.jpa; import javax.persistence.*; @Entity @Table(name="student") @NamedQuery(name = "find name" , query = "Select s from StudentEntity s") public class StudentEntity {@Idprivate 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; } }

Persistence.xml

< 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>

FetchColumn.java

package com.srcmini.jpa.jpql; import javax.persistence.*; import com.srcmini.jpa.StudentEntity; import java.util.*; public class FetchColumn { public static void main( String args[]) {EntityManagerFactory emf = Persistence.createEntityManagerFactory( "Student_details" ); EntityManager em = emf.createEntityManager(); em.getTransaction().begin( ); Query query = em.createNamedQuery("find name"); @SuppressWarnings("unchecked")List< StudentEntity> list =query.getResultList(); System.out.println("Student Name :"); for(StudentEntity s:list) {System.out.println(s.getS_name()); }em.close(); emf.close(); } }