Java - Hibernate criteria.setResultTransformer（）用默认值初始化模型字段

问题描述

我是Hibernate的新手，我试图从数据库中获取一些数据。我不希望获得完整的数据，而是实体的投影。

事情是，在for循环中，当我得到id和名称我的投影，它获取默认值id = 0和name = null，而不是id = 7和name =Name 8，它们是数据库中原始实体的记录。你知道是什么原因导致这个问题？
for循环在最后一个代码中。

这是学生实体

<$ p $ @Entity（name =Students）
public class Student {
@Id
@GeneratedValue
@Column（name =StudentId）
private int id;

@Column（name =Name，nullable = false，length = 50）
私有字符串名称;

@Column（name =Grade）
private Double grade = null;

@ManyToOne（cascade = CascadeType.PERSIST）
@JoinColumn（name =FacultyId，nullable = false）
私立教职员;

@ManyToMany（cascade = CascadeType.PERSIST）
@JoinTable（
joinColumns = @JoinColumn（name =StudentId），
inverseJoinColumns = @JoinColumn（name =CourseId））
private Collection< Course>培训班;

public Student（）{
this.courses = new HashSet< Course>（）;
}

//所有字段的Setters和Getters
}


这是StudentModel

  public class StudentModel {
 private int id; 
私人字符串名称; 
 
 public int getId（）{
 return this.id; 
} 
 
 public void setId（int id）{
 this.id = id; 
} 
 
 public String getName（）{
 return this.name; 
} 
 
 public void setName（String name）{
 this.name = name; 
 
 
  

我正在执行的代码

  Session session = sessionFactory.openSession（）; 
 session.beginTransaction（）; 
 {
 Criteria criteria = session.createCriteria（Student.class）; 
 criteria.add（Restrictions.eq（name，Name 8））
 .setProjection（
 Projections.projectionList（）
 .add（Projections.property（ id）））
 .add（Projections.property（name）））
 .setResultTransformer（
 Transformers.aliasToBean（StudentModel.class））; 
 
 @SuppressWarnings（unchecked）
 List< StudentModel> students = criteria.list（）; （StudentModel student：students）
 
 {
 System.out.println（student.getId（））; 
 System.out.println（student.getName（））; 
} 
 
 session.getTransaction（）。commit（）; 
 session.close（）; 
 
  

解决方案

别名到您的预测：

  Projections.projectionList（）
 .add（Projections.property（id）， id）
 .add（Projections.property（name），name）
  

I am new to Hibernate and I am trying to get some data from the database. I don't want to get the full data but a projection of an entity.

The thing is that in the for-loop when I get the id and the name of my projection, it gets the default values id=0 and name=null instead of id=7 and name="Name 8" which are the records of the original entity in the database. Do you know what causes this problem?The for-loop is in the last code.

Here is the Student Entity

@Entity(name = "Students")
public class Student {
    @Id
    @GeneratedValue
    @Column(name = "StudentId")
    private int id;

    @Column(name = "Name", nullable = false, length = 50)
    private String name;

    @Column(name = "Grade")
    private Double grade = null;

    @ManyToOne(cascade = CascadeType.PERSIST)
    @JoinColumn(name = "FacultyId", nullable = false)
    private Faculty faculty;

    @ManyToMany(cascade = CascadeType.PERSIST)
    @JoinTable(
        joinColumns = @JoinColumn(name = "StudentId"),
        inverseJoinColumns = @JoinColumn(name = "CourseId"))
    private Collection<Course> courses;

    public Student() {
        this.courses = new HashSet<Course>();
    }

    // Setters and Getters for all fields
}

Here is the StudentModel

public class StudentModel {
    private  int id;
    private String name;

    public int getId() {
        return this.id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return this.name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

And the code I am executing

Session session = sessionFactory.openSession();
    session.beginTransaction();
    {
        Criteria criteria = session.createCriteria(Student.class);
        criteria.add(Restrictions.eq("name", "Name 8"))
                .setProjection(
                        Projections.projectionList()
                                .add(Projections.property("id"))
                                .add(Projections.property("name")))
                .setResultTransformer(
                        Transformers.aliasToBean(StudentModel.class));

        @SuppressWarnings("unchecked")
        List<StudentModel> students = criteria.list();

        for (StudentModel student : students) {
            System.out.println(student.getId());
            System.out.println(student.getName());
        }

        session.getTransaction().commit();
        session.close();
    }

解决方案

You probably simply forgot to assign aliases to your projections:

Projections.projectionList()
           .add(Projections.property("id"), "id")
           .add(Projections.property("name"), "name")

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