我正在尝试在一个非常简单的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查询只是将Employees左连接到Departments。
我已经按照Hibernate文档中指定的注释设置进行了设置,但每当我尝试序列化实体时,Hibernate就会进入无限循环,并最终抛出StackOverFlowError异常。回答我的另一个问题的人能够确定堆栈溢出是因为"Department"对象包含一组"Employee"对象,每个对象都包含一个"Department"对象,其中包含一组Employee对象,依此类推。
这种双向关系应该是合法的,根据上面链接的文档(Department中的“mappedBy”参数应该能够提示Hibernate;我还尝试使用了下面代码中被注释掉的“joinColumn”注解),我读到的其他信息表明Hibernate应该聪明到不会在这种情况下进入无限循环,但是对于我的示例却没有起作用。如果我通过从Employee类中删除Department对象将双向关系改为单向关系,则一切正常运行,但显然这会导致许多功能的丧失。
我还尝试放弃旧的xml映射文件的注释,并为子表设置“inverse”参数,但仍然产生相同的问题。我该如何使这种双向关系按照预期工作?
部门:
员工:
我已经按照Hibernate文档中指定的注释设置进行了设置,但每当我尝试序列化实体时,Hibernate就会进入无限循环,并最终抛出StackOverFlowError异常。回答我的另一个问题的人能够确定堆栈溢出是因为"Department"对象包含一组"Employee"对象,每个对象都包含一个"Department"对象,其中包含一组Employee对象,依此类推。
这种双向关系应该是合法的,根据上面链接的文档(Department中的“mappedBy”参数应该能够提示Hibernate;我还尝试使用了下面代码中被注释掉的“joinColumn”注解),我读到的其他信息表明Hibernate应该聪明到不会在这种情况下进入无限循环,但是对于我的示例却没有起作用。如果我通过从Employee类中删除Department对象将双向关系改为单向关系,则一切正常运行,但显然这会导致许多功能的丧失。
我还尝试放弃旧的xml映射文件的注释,并为子表设置“inverse”参数,但仍然产生相同的问题。我该如何使这种双向关系按照预期工作?
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;
}
}