JPA JPQL 基本操作

2024 年 8 月 29 日 | 阅读 2 分钟

JPQL 允许我们创建静态和动态查询。现在，我们将使用以下类型的查询，在下表中执行一些基本的 JPQL 操作。

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.javatpoint.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.javatpoint.jpa.StudentEntity</class>

      <properties>
         <property name="javax.persistence.jdbc.driver" value="com.mysql.jdbc.Driver"/>
         <property name="javax.persistence.jdbc.url" value="jdbc:mysql://:3306/studentdata"/>
         <property name="javax.persistence.jdbc.user" value="root"/>
         <property name="javax.persistence.jdbc.password" value=""/>
         <property name="eclipselink.logging.level" value="SEVERE"/>
         <property name="eclipselink.ddl-generation" value="create-or-extend-tables"/>
      </properties>
      
   </persistence-unit>
</persistence>

FetchColumn.java

package com.javatpoint.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

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。

StudentEntity.java

package com.javatpoint.jpa;
	import javax.persistence.*;

	@Entity
	@Table(name="student")
	@NamedQuery(name = "find name" , query = "Select s from StudentEntity s")
	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.javatpoint.jpa.StudentEntity</class>

      <properties>
         <property name="javax.persistence.jdbc.driver" value="com.mysql.jdbc.Driver"/>
         <property name="javax.persistence.jdbc.url" value="jdbc:mysql://:3306/studentdata"/>
         <property name="javax.persistence.jdbc.user" value="root"/>
         <property name="javax.persistence.jdbc.password" value=""/>
         <property name="eclipselink.logging.level" value="SEVERE"/>
         <property name="eclipselink.ddl-generation" value="create-or-extend-tables"/>
      </properties>
      
   </persistence-unit>
</persistence>

FetchColumn.java

package com.javatpoint.jpa.jpql;
import javax.persistence.*;

import com.javatpoint.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();  
	 }
	

}