4

我试图在一个非常简单的 Hibernate 示例中填充一些实体对象。我的数据库由两个表组成，“Departments”（Id，Name）和“Employees”（Id，DepartmentsId，FirstName，LastName）。我的 SQL 查询只是员工到部门的左连接。

我已经按照Hibernate 文档中的说明设置了注释，但是每当我尝试序列化实体时，Hibernate 都会进入无限循环并最终引发 StackOverFlowError 异常。回答我的另一个问题的人能够确定堆栈溢出正在发生，因为“部门”对象包含一组“员工”对象，每个对象都包含一个“部门”对象，其中包含一组员工对象等。等等

根据上面链接的文档，这种类型的双向关系应该是合法的（Department 中的“mappedBy”参数应该提示 Hibernate；我还尝试使用在下面的代码中注释掉的“joinColumn”注释） ，以及我读过的其他内容表明 Hibernate应该足够聪明，不会在这种情况下进入无限循环，但它不适用于我的示例。如果我通过从 Employee 类中删除 Department 对象将双向关系更改为单向关系，一切正常，但显然这会导致很多功能的丢失。

我也尝试过为较旧的 xml 映射文件设置注释并为子表设置“反向”参数，但它仍然产生相同的问题。我怎样才能让这种双向关系按照它应该的方式工作？

部门：

package com.test.model;

import java.util.HashSet;
import java.util.Set;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.JoinTable;

import static javax.persistence.GenerationType.IDENTITY;
import javax.persistence.Id;
import javax.persistence.OneToMany;
import javax.persistence.Table;
import javax.persistence.JoinColumn;

import org.hibernate.Hibernate;
import org.hibernate.proxy.HibernateProxy;

@Entity
@Table(name="Departments"
,catalog="test"
)
public class Department implements java.io.Serializable {

 private Integer id;
 private String name;
 public Set<Employee> employees = new HashSet<Employee>(0);

public Department() {
}


public Department(String name) {
    this.name = name;
}
public Department(String name, Set employees) {
   this.name = name;
   this.employees = employees;
}

 @Id @GeneratedValue(strategy=IDENTITY)


@Column(name="Id", unique=true, nullable=false)
public Integer getId() {
    return this.id;
}

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


@Column(name="Name", nullable=false)
public String getName() {
    return this.name;
}

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

@OneToMany(fetch=FetchType.LAZY, mappedBy="department")
/*@OneToMany
@JoinColumn(name="DepartmentsId")*/
public Set<Employee> getEmployees() {
    return this.employees;
}

public void setEmployees(Set employees) {
    this.employees = employees;
}
}

员工：

package com.test.model;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.JoinTable;

import static javax.persistence.GenerationType.IDENTITY;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;
import javax.persistence.Table;

@Entity
@Table(name="Employees"
,catalog="test"
)
public class Employee  implements java.io.Serializable {


 private Integer id;
 private Department department;
 private String firstName;
 private String lastName;

public Employee() {
}

public Employee(Department department, String firstName, String lastName) {
   this.department = department;
   this.firstName = firstName;
   this.lastName = lastName;
}

 @Id @GeneratedValue(strategy=IDENTITY)


@Column(name="Id", unique=true, nullable=false)
public Integer getId() {
    return this.id;
}

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

@ManyToOne
@JoinColumn(name="DepartmentsId", nullable=false, insertable=false, updatable=false)
public Department getDepartment() {
    return this.department;
}

public void setDepartment(Department department) {
    this.department = department;
}


@Column(name="FirstName", nullable=false)
public String getFirstName() {
    return this.firstName;
}

public void setFirstName(String firstName) {
    this.firstName = firstName;
}


@Column(name="LastName", nullable=false)
public String getLastName() {
    return this.lastName;
}

public void setLastName(String lastName) {
    this.lastName = lastName;
}
}

部门经理（包含 HQL 查询）：

package com.test.controller;

import java.util.Collections;
import java.util.List;

import java.util.Iterator;

import org.hibernate.Criteria;
import org.hibernate.Hibernate;
import org.hibernate.HibernateException;
import org.hibernate.Query;
import org.hibernate.Session;

import com.test.model.Department;
import com.test.util.HibernateUtil;

public class DepartmentManager extends HibernateUtil {
public List<Department> list() {
    Session session = HibernateUtil.getSessionFactory().getCurrentSession();
    session.beginTransaction();
    List<Department> set = null;
    try {
        Query q = session.createQuery("FROM Department d JOIN FETCH d.employees e");
        q.setResultTransformer(Criteria.DISTINCT_ROOT_ENTITY);
        set = (List<Department>) q.list();
    } catch (HibernateException e) {
        e.printStackTrace();
        session.getTransaction().rollback();
    }
    session.getTransaction().commit();
    return set;
}
}
4

2 回答 2

7

通常，您不应该序列化您的实体。循环依赖和代理使这变得困难。相反，您应该手动将需要发送的数据传输到 DTO（一个新的纯数据类），然后将其序列化。它不会有惰性集合、代理和诸如此类的东西。

于 2012-04-22T08:22:29.757 回答
0

为了补充顶部响应，我做了一个通用转换谁为我做这项工作，将实体值传输到 DTO 对象，您只需使您的 dto 字段与映射实体中的名称相同。

这是源代码。

/** * Atribui os valores de campos通讯员de um objeto para um outro objeto de destino。Os * campos do objeto de destino que ja estiverem preenchidos nao serao substituidos * * @param objetoOrigem * @param objetoDestino * @return * @throws NegocioException */

public static <T1, T2> T2  convertEntity(T1 objetoOrigem, T2 objetoDestino) throws NegocioException {

    if (objetoOrigem != null && objetoDestino != null) {
        Class<? extends Object> classe = objetoOrigem.getClass();
        Class<? extends Object> classeDestino = objetoDestino.getClass();

        Field[] listaCampos = classe.getDeclaredFields();
        for (int i = 0; i < listaCampos.length; i++) {
            Field campo = listaCampos[i];
            try {
                Field campoDestino = classeDestino.getDeclaredField(campo.getName());
                campo.setAccessible(true);
                campoDestino.setAccessible(true);
                atribuiValorAoDestino(objetoOrigem, objetoDestino, campo, campoDestino);
            } catch (NoSuchFieldException e) {
                LOGGER.log(Logger.Level.TRACE, (Object) e);
                continue;
            } catch (IllegalArgumentException | IllegalAccessException e) {
                LOGGER.error(e.getMessage(), e);
                throw new NegocioException(e.getMessage(), EnumTypeException.ERROR);
            }
        }
    }
    return objetoDestino;
}
于 2016-04-29T13:53:49.707 回答