Question

我是Hibernate标准的新手，Tutor和Student之间的关系是OneToMany（即一个Tutor有很多Student），我试过以下hibernate查询检索所有导师姓名为Peter Smith的学生：

from Student student where student.tutor.name is 'Peter Smith'

并获得以下结果：

Shin Don
Robert Cage

然后我尝试使用Hibernate Criteria API进行以下相同的查询：

Criteria criteria = session.createCriteria(Student.class);  
criteria.createCriteria("tutor").add(Restrictions.eq("name", "Peter Smith"));
criteria.list();

这次我得到以下结果：

Shin Don
Shin Don
Robert Cage 
Robert Cage

以下是我的学生和导师实体：

Student.java

@Entity
public class Student {

    private Integer id;
    private String studentId;
    private String name;
    private Tutor tutor;
    //remaining fields

    public Student() {}
    public Student(String studentId, String name) {
        super();
        this.studentId = studentId;
        this.name = name;
    }

    @Id
    @GeneratedValue
    public Integer getId() {
        return id;
    }

    @Column(unique=true, nullable=false)
    public String getStudentId() {
        return studentId;
    }

    @ManyToOne
    @JoinColumn(name="tutor_id")
    public Tutor getTutor() {
        return tutor;
    }

    @Override
    public int hashCode() {
        //returns hashcode based on studentId
    }
    @Override
    public boolean equals(Object obj) {
        //returns true or false based on studentId
    }
    @Override
    public String toString() {
        return this.name;
    }

    //remaining getter and setter methods

}

Tutor.java

@Entity
public class Tutor{

    private Integer id;
    private String tutorId;
    private String name;
    private Set<Student> students = new HashSet<Student>();
    //remaining fields

    public Tutor() {}   
    public Tutor(String tutorId, String name) {
        super();
        this.tutorId = tutorId;
        this.name = name;
    }

    @Id
    @GeneratedValue
    public Integer getId() {
        return id;
    }

    @Column(unique=true, nullable=false)
    public String getTutorId() {
        return tutorId;
    }

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

    @Override
    public int hashCode() {
        //returns hashcode based on tutorId
    }
    @Override
    public boolean equals(Object obj) {
        //returns true or false based on tutorId
    }

    public void addStudent(Student student) {
        this.students.add(student);
        student.setTutor(this);
    }

    //remaining setter and getter methods

}

对于HQL，我得到以下SQL：

select
...
...
from
    Tutor tutor0_ 
left outer join
    Student students1_ 
        on tutor0_.id=students1_.tutor_id 
where
    tutor0_.id=?

对于标准，我得到以下SQL：

select
...
...
from
    Student this_ 
inner join
    Tutor tutor1_ 
        on this_.tutor_id=tutor1_.id 
left outer join
    Student students4_ 
        on tutor1_.id=students4_.tutor_id 
where
    tutor1_.name=?

有人可以帮助我理解为什么我没有得到与给定的HQL和标准相同的结果？

感谢。

Answer 1

更改Tutor.java

     @OneToMany(mappedBy="tutor", targetEntity=Student.class,
cascade=CascadeType.ALL, fetch=FetchType.EAGER)

到

     @OneToMany(mappedBy="tutor", targetEntity=Student.class,
cascade=CascadeType.ALL, fetch=FetchType.LAZY)

Hibernate Criteria API和Hibernate查询语言之间的结果冲突

1 个答案: