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java - JPA 不同的内部联接与联接表上的条件

问题描述

我在下面有两个表：

@Entity
@Table(name="COLLEGE")
public class College {
private Long collegeId;
private List<Student> students;

@Id
@Column(name = "COLLEGE_ID")
public Long getCollegeId() {
       return this.collegeId;
   }

public void setCollegeId(final Long collegeId) {
       this.collegeId= collegeId;
   }
 @OneToMany(cascade = CascadeType.ALL, fetch = FetchType.LAZY, mappedBy = "college")
 @Cascade(org.hibernate.annotations.CascadeType.DELETE_ORPHAN)
public List<Student> getStudents() {
        if (this.students== null) {
            this.students= new ArrayList<>();
        }
        return this.students;
    }
public void setStudents(List<Student> students){
     this.students = students
    }
}




@Entity
@Table(name="STUDENT")
public class Student {
   private Long studentId;
   private College college;
   private String name;
   private String department;

@Id
public Long getStudentId() {
    return this.studentId;
  }
public void setStudentId(Long studentId) {
    this.studentId = studentId;
 }

@ManyToOne(fetch = FetchType.LAZY) 
@JoinColumn(name = "COLLEGE_ID")
public getCollege() {
    return this.college;
  }
public setCollege(College college) {
    this.college = college;
  }
  ......
  ......
}

我想获取带有特定college列表的对象。SQL查询如下：studentsdepartment

select *
from COLLEGE c
inner join STUDENT s on c.COLLEGE_ID= s.collegeId
where c.COLLEGE_ID=12345 and s.DEPARTMENT="ENGINEERING";

到目前为止，我已经尝试了下面的 JPA 查询，但它返回了多个College对象。

SELECT DISTINCT c
FROM COLLEGE c
INNER JOIN c.students s
where c.collegeId= :collegeid and s.department = :department

如何返回带有过滤college列表的单个对象？studentsdepartment

注意：我无法更改此处使用的实体对象。

标签： javasqloraclejpajpql

解决方案

尝试使用此查询，JOIN FETCH改为使用INNER JOIN：

SELECT DISTINCT c FROM College c 
       JOIN FETCH c.students s
            WHERE c.collegeId= :collegeid 
                  AND s.department = :department

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