JPQL联表查询，返回结果整合联表的两个实体结果

sql代码

package com.sys.service;

import java.util.List;

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

import org.springframework.stereotype.Service;
import org.springframework.transaction.annotation.Transactional;

import com.sys.entity.GradeStudent;

@Service
@Transactional
public class CommentService {
	@PersistenceContext
	EntityManager em;

	@SuppressWarnings("unchecked")
	public List getGradeStudents() {
		String sql = "select new com.sys.entity.GradeStudent(s.name,s.idCard,g.gradeName) "
				+ "from Student s,Grade g where s.idGrade=g.id order by g.gradeName";
		Query query = em.createQuery(sql);
		List list = query.getResultList();

		return list;
	}
}

Student实体

package com.sys.entity;

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

@Entity
public class Student {
	
	private int id;
	private String name;
	private String idCard;
	private int idGrade;
	
	@Id
	@GeneratedValue
	public int getId() {
		return id;
	}
	public void setId(int id) {
		this.id = id;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	
	/**
	 * @return the idCard
	 */
	public String getIdCard() {
		return idCard;
	}
	/**
	 * @param idCard the idCard to set
	 */
	public void setIdCard(String idCard) {
		this.idCard = idCard;
	}
	public int getIdGrade() {
		return idGrade;
	}
	public void setIdGrade(int idGrade) {
		this.idGrade = idGrade;
	}
	
	
}

Grade实体

package com.sys.entity;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;

@Entity
public class Grade {

	private int id;
	private String gradeName;
	
	@Id
	@GeneratedValue(strategy=GenerationType.AUTO)
	public int getId() {
		return id;
	}
	public void setId(int id) {
		this.id = id;
	}
	public String getGradeName() {
		return gradeName;
	}
	public void setGradeName(String gradeName) {
		this.gradeName = gradeName;
	}
	
	
}

联表查询后杂交实体代码：

package com.sys.entity;


//@Entity
public class GradeStudent {
	private int id;
	private String name;
	private String idCard;
	private String gradeName;
	
	public GradeStudent() {
	}
	
	public GradeStudent(String name, String idCard, String gradeName) {
		super();
		this.name = name;
		this.idCard = idCard;
		this.gradeName = gradeName;
	}

	/*@Id
	@GeneratedValue*/
	public int getId() {
		return id;
	}
	public void setId(int id) {
		this.id = id;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public String getIdCard() {
		return idCard;
	}
	public void setIdCard(String idCard) {
		this.idCard = idCard;
	}
	public String getGradeName() {
		return gradeName;
	}
	public void setGradeName(String gradeName) {
		this.gradeName = gradeName;
	}
	
}

要点提示：联表查询的的实体类 都要有实体标志 @Entity 、@Id   返回的杂交实体不需要有实体注解，但要有个构造器。

JPQL查询语言中

select new com.sys.entity.GradeStudent(s.name,s.idCard,g.gradeName) from Student s,Grade g where s.idGrade=g.id order by g.gradeName

实体 是全路径

com.sys.entity.GradeStudent(s.name,s.idCard,g.gradeName)