休眠插入到集合会导致删除，然后再次插入集合中的所有项目 [英] hibernate insert to a collection causes a delete then all the items in the collection to be inserted again

问题描述

我有很多关系 CohortGroup 和 Employee.每当我将员工插入 CohortGroup 时，休眠都会从解析表中删除该组并再次插入所有成员，以及新成员.为什么不直接添加新的?

I have a many to may relationship CohortGroup and Employee. Any time I insert an Employee into the CohortGroup hibernate deletes the group from the resolution table and inserts all the members again, plus the new one. Why not just add the new one?

组内注解:

@ManyToMany(cascade = { PERSIST, MERGE, REFRESH })
@JoinTable(name="MYSITE_RES_COHORT_GROUP_STAFF",
joinColumns={@JoinColumn(name="COHORT_GROUPID")},
inverseJoinColumns={@JoinColumn(name="USERID")})
public List<Employee> getMembers(){
  return members;
}

员工的另一面

@ManyToMany(mappedBy="members",cascade = { PERSIST, MERGE, REFRESH } )
public List<CohortGroup> getMemberGroups(){
  return memberGroups;
}

代码片段

Employee emp = edao.findByID(cohortId);
CohortGroup group = cgdao.findByID(Long.decode(groupId));
group.getMembers().add(emp);
cgdao.persist(group);

下面是日志上报的sql

below is the sql reported in the log

delete from swas.MYSITE_RES_COHORT_GROUP_STAFF where COHORT_GROUPID=?
insert into swas.MYSITE_RES_COHORT_GROUP_STAFF (COHORT_GROUPID, USERID) values (?, ?)
insert into swas.MYSITE_RES_COHORT_GROUP_STAFF (COHORT_GROUPID, USERID) values (?, ?)
insert into swas.MYSITE_RES_COHORT_GROUP_STAFF (COHORT_GROUPID, USERID) values (?, ?)
insert into swas.MYSITE_RES_COHORT_GROUP_STAFF (COHORT_GROUPID, USERID) values (?, ?)
insert into swas.MYSITE_RES_COHORT_GROUP_STAFF (COHORT_GROUPID, USERID) values (?, ?)
insert into swas.MYSITE_RES_COHORT_GROUP_STAFF (COHORT_GROUPID, USERID) values (?, ?)

这种接缝确实效率低下，并导致了一些问题.如果多次请求将员工添加到组中，则有些请求会被覆盖.

This seams really inefficient and is causing some issues. If sevral requests are made to add an employee to the group then some get over written.

像equals和hashCode这样的接缝可能是造成这种情况的原因.下面是这些方法的实现.任何危险信号?

Seams like equals and hashCode might be a reason for this. Below are the implementation for these methods. Any red flags?

同类群组

    @Override
public int hashCode() {
    final int prime = 31;
    int result = getName().hashCode();
    result = prime * result + ((emp == null) ? 0 : emp.hashCode());
    return result;
}
@Override
public boolean equals(Object obj) {
    if (this == obj) {return true;}
    if (!(obj instanceof CohortGroup)) {return false;}
    CohortGroup other = (CohortGroup) obj;
    if(!getName().equals(other.getName())){return false;}
    if (emp == null && other.getOwner() != null) {
        return false;
    } else if (!emp.equals(other.getOwner())) {
        return false;
    }
    return true;
}

员工

       @Override
public boolean equals(Object obj) {
    if (this == obj) {return true;}
    if (obj == null) {return false;}
    if (!(obj instanceof Employee)) {return false;}
    Employee other = (Employee) obj;
    if (EMPLID == null && other.getEMPLID() != null) {
        return false;
    } else if (!EMPLID.equals(other.getEMPLID())) {
        return false;
    }
    return true;
}

   @Override
public int hashCode() {
    final int prime = 31;
    int result = 1;
    result = prime * result + ((EMPLID == null) ? 0 : EMPLID.hashCode());
    return result;
}

我向 CohortGroup 添加了一个 addMember 方法，该方法添加到关系的双方:

I have added an addMember method to the CohortGroup that adds to both sides of the relationship:

    public void addMember(Employee emp){
    this.getMembers().add(emp);
    emp.getMemberGroups().add(this);

}

继续感谢所有提供帮助的人.

Continued thanks to all that are helping.

推荐答案

我现在已经按照我期望的方式执行了插入操作.感谢Pascal和z5h，我学到了很多.我相信我已经正确实现了 hashCode 和 equals.但这从来没有为我解决问题.相反，我实现了一个中间实体.

I have inserts acting the way I expect them to now. Thanks to Pascal and z5h, I have learned a lot. I believe I have the hashCode and equals implemented correctly. This never solved the problem for me though. Instead I have implemented an Intermediate Entity.

下面值得一提的是我的 Employee、CohortGroup 和现在的 CohortGroupMemeber 类中的映射.

For what it is worth below are the mapping in my Employee, CohortGroup, and now CohortGroupMemeber classes.

员工:

@OneToMany(mappedBy="member")
public List<CohortGroupMember> getMemberGroups(){
   return memberGroups;
}
public void setMemberGroups(List<CohortGroupMember> grps){
   memberGroups = grps;
}

群组成员

@ManyToOne
@JoinColumn(name="USERID")
public Employee getMember(){
    return emp;
}
public void setMember(Employee e){
    emp = e;
}
@ManyToOne
@JoinColumn(name="COHORT_GROUPID")
public CohortGroup getGroup(){
    return group;
}
public void setGroup(CohortGroup cg){
    group   = cg;
}

同类群组

@OneToMany(mappedBy="group")
public List<CohortGroupMember> getMembers(){
    return members;
}
public void setMembers(List<CohortGroupMember> emps){
    members = emps;
}

我遵循的这本书是 Java Persistence with Hibernate 章节 7.2.3

The book I followed for this is Java Persistence with Hibernate chapter 7.2.3

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