休眠一对多映射渴望获取不起作用

Question

学院与学生实体之间存在一对多的关系。

学院

@Entity
public class College {

private int collegeId;
private String collegeName;
private List<Student> students;

@Id
@GeneratedValue
public int getCollegeId() {
    return collegeId;
}

public void setCollegeId(int collegeId) {
    this.collegeId = collegeId;
}

public String getCollegeName() {
    return collegeName;
}

public void setCollegeName(String collegeName) {
    this.collegeName = collegeName;
}

@OneToMany(targetEntity=Student.class, mappedBy="college", cascade=CascadeType.ALL, fetch=FetchType.EAGER ) 
public List<Student> getStudents() {
    return students;
}

public void setStudents(List<Student> students) {
    this.students = students;
}

}

学生

@Entity
public class Student {

private int studentId;
private String studentName;
private College college;

@Id
@GeneratedValue
public int getStudentId() {
    return studentId;
}

public void setStudentId(int studentId) {
    this.studentId = studentId;
}

public String getStudentName() {
    return studentName;
}

public void setStudentName(String studentName) {
    this.studentName = studentName;
}

@ManyToOne
@JoinColumn(name="college_id")
public College getCollege() {
    return college;
}

public void setCollege(College college) {
    this.college = college;
}

}

我是休眠的新手，因此根据我的理解，如果我将fetchtype设置为FetchType.EAGER那么每当我查询单个大学对象相关学生对象时，都会自动获取。我使用了以下查询，

College college = (College) session.get(College.class, id);

正确加载了college对象，但是当我返回college.getStudents() ，我将得到null 。 我是否缺少某些东西，或者这是正确获取古怪的东西的正确方法？

Answer 1

您的代码看起来还不错，但是您可以尝试以下操作，让我们知道它是否有效。

您在College.java中的代码行：

@OneToMany(targetEntity=Student.class, mappedBy="college", cascade=CascadeType.ALL, fetch=FetchType.EAGER ) 
public List<Student> getStudents() {
    return students;
}

请尝试将其替换为：

@OneToMany(targetEntity=Student.class, mappedBy="college", cascade=CascadeType.ALL, fetch=FetchType.EAGER ) 
@JoinColumn(name="college_id") // join column is in table for Student
public List<Student> getStudents() {
    return students;
}

希望这对您有所帮助。