我们在使用hibernate或JPA的一对多、多对一进行删除操作的时候常会出现org.hibernate.ObjectDeletedException: deleted entity passed to persist: [xxx#<null>]的错误,这是怎么引起的呢?又该怎么解决?在这里说说我自己的看法,欢迎不同见解。
以使用JPA+Spring为例,建立deparment(部门)、user(人员)两个实体类:
package com.yg.bean.user; import java.util.HashSet; import java.util.Set; import javax.persistence.Column; import javax.persistence.Entity; import javax.persistence.FetchType; import javax.persistence.Id; import javax.persistence.OneToMany; /** * 部门信息实体类 * @author: LiChao * date: Nov 6, 2012 -- 3:03:39 PM */ @Entity public class Department { /*部门编号*/ private String code; /*部门名称*/ private String name; /*部门内员工*/ private Set<User> users = new HashSet<User>(); public Department() {} public Department(String code) { this.code = code; } public Department(String code, String name) { this.code = code; this.name = name; } @Id @Column(length=12,nullable=false) public String getCode() { return code; } public void setCode(String code) { this.code = code; } @Column(length=60,nullable=false) public String getName() { return name; } public void setName(String name) { this.name = name; } @OneToMany(mappedBy="dwdm",fetch=FetchType.EAGER) public Set<User> getUsers() { return users; } public void setUsers(Set<User> users) { this.users = users; } @Override public int hashCode() { final int prime = 31; int result = 1; result = prime * result + ((code == null) ? 0 : code.hashCode()); return result; } @Override public boolean equals(Object obj) { if (this == obj) return true; if (obj == null) return false; if (getClass() != obj.getClass()) return false; final Department other = (Department) obj; if (code == null) { if (other.code != null) return false; } else if (!code.equals(other.code)) return false; return true; } }
package com.yg.bean.user; import javax.persistence.CascadeType; import javax.persistence.Column; import javax.persistence.Id; import javax.persistence.JoinColumn; import javax.persistence.ManyToOne; import org.hibernate.annotations.NotFound; import org.hibernate.annotations.NotFoundAction; /** * 系统用户信息实体类 * @author: LiChao * date: Nov 6, 2012 -- 3:45:02 PM */ public class User1 { /*id*/ private String id; /*用户名*/ private String name; /**/ private Integer age; /*部门*/ private Department dep; @Id @Column(length=6,nullable=false) public String getId() { return id; } public void setId(String id) { this.id = id; } @Column(length=30,nullable=true) public String getName() { return name; } public void setName(String name) { this.name = name; } @Column(nullable=true) public Integer getAge() { return age; } public void setAge(Integer age) { this.age = age; } @ManyToOne(cascade=CascadeType.REFRESH) @JoinColumn(name="dep") @NotFound(action=NotFoundAction.IGNORE) public Department getDep() { return dep; } public void setDep(Department dep) { this.dep = dep; } }
当我们在删除user表中的记录的时候就会报我们之前提到的异常,这是什么原因呢?细心的朋友可能注意到了,在depatment实体中department对user为一对多关系,并且加载方式为“立即加载”(fetch=FetchType.EAGER),关键就在这里,你可以简单理解为当你调用了department实体后,就会立即得到对表user的数据的引用,所以你再对user表中的数据经行删除的时候是不被允许的。解决方法我想到了两种:
1、最简单的方法:抓取策略改为懒加载方式(fetch=FetchType.LAZY)。但是这种方法在你调用department.getUsers();后再进行删除user表中记录的操作的时候仍会报相同异常,并且还极有可能报session已关闭异常。
2、比较完美的方法:department.getUsers().clear();为防止session已关闭异常,我们有时候必须将加载策略设为立即加载,怎么完美解决呢?很简单!在你删除user表中数据前先执行department.getUsers().clear();就可以了,你可以理解为:清除对user表数据的引用。