相关疑难解决方法(0)

在我的DAO层中,我有一个像这样的Find函数

public List<?> findCategoryWithSentenceNumber(int offset, int maxRec) {
  Criteria crit = getSession().createCriteria(Category.class, "cate");
    crit.createAlias("cate.sentences", "sent");

    crit.setProjection(Projections.projectionList().
    add(Projections.property("title"), "title").
    add(Projections.count("sent.id"), "numberOfSentence").
    add(Projections.groupProperty("title"))
  );

  crit.setFirstResult(offset);
  crit.setMaxResults(maxRec);

  return crit.list();
}

所以,为了读取数据,我必须使用一个循环(带Iterator)

List<?> result = categoryDAO.findCategoryWithSentenceNumber(0, 10);
// List<DQCategoryDTO> dtoList = new ArrayList<>(); 

for (Iterator<?> it = result.iterator(); it.hasNext(); ) {
  Object[] myResult = (Object[]) it.next();

  String  title = (String) myResult[0];
  Long count = (Long) myResult[1];


  assertEquals("test", title); 
  assertEquals(1, count.intValue()); 

  // dQCategoryDTO = new DQCategoryDTO();
  // dQCategoryDTO.setTitle(title);
  // dQCategoryDTO.setNumberOfSentence(count);
  // dtoList.add(dQCategoryDTO);

} …

我有一个表"课",它与表"学生"和"老师"相关联.通过外围关键关系将"班级"与多个学生和教师联系起来.

当我使用hibernate关联并获取大量实体(尝试5000)时,我发现它占用的内存比使用外键占位符的内存多4倍.hibernate关联有什么问题吗？

我可以使用任何内存分析器来找出使用太多内存的内容吗？

这是架构的方式:

class(id,className) 

student(id,studentName,class_id)
teacher(id,teacherName,class_id)

class_id is foreign key..

案例#1 - Hibernate协会

1)在班级实体中,将学生和教师映射为:

@Entity
@Table(name="class")
public class Class {

private Integer id;
private String className;

private Set<Student> students = new HashSet<Student>();
private Set<Teacher> teachers = new HashSet<Teacher>();

@OneToMany(fetch = FetchType.EAGER, mappedBy = "classRef")
@Cascade({ CascadeType.ALL })
@Fetch(FetchMode.SELECT)
@BatchSize(size=500)
public Set<Student> getStudents() {
    return students;
}

2)在学生和老师中,映射类为:

@Entity
@Table(name="student")
public class Student {

private Integer id;
private String studentName;
private Class classRef;

@ManyToOne
@JoinColumn(name = "class_id")
public Class getClassRef() …