如何在不删除实际目标实体的情况下删除@ManyToMany关联(已加入链接)

Question

我正在开发一个Spring MVC应用程序，其中有多对多映射。有3个表，一个是GroupAccount、memberjunction、GroupMembers。现在，当我删除groupMember时，我只想从GroupMembers和memberjunction中删除与memberId对应的条目。我尝试使用Cascade.Remove，它也导致了GroupAccount的删除。我正在发布我的sql代码，以及到目前为止我所拥有的。

SQL代码：

CREATE TABLE groupaccount
(
  groupid numeric NOT NULL,
  groupname character varying,
  adminusername character varying,
  CONSTRAINT groupid PRIMARY KEY (groupid)
)
CREATE TABLE memberjunction
(
  memberid integer NOT NULL,
  groupid numeric NOT NULL,
  CONSTRAINT membergroupid PRIMARY KEY (memberid, groupid),
  CONSTRAINT groupaccount_memberjunction_fk FOREIGN KEY (groupid)
      REFERENCES groupaccount (groupid) MATCH SIMPLE
      ON UPDATE NO ACTION ON DELETE NO ACTION,
  CONSTRAINT groupmembers_memberjunction_fk FOREIGN KEY (memberid)
      REFERENCES groupmembers (memberid) MATCH SIMPLE
      ON UPDATE NO ACTION ON DELETE NO ACTION
)
CREATE TABLE groupmembers
(
  memberid integer NOT NULL,
  musername character varying,
  accesslevel boolean DEFAULT true,
  CONSTRAINT memberid PRIMARY KEY (memberid)
)

GroupMembersDAOImpl删除方法：

@Override
public boolean removeGroupMember(int memberId) {
    session = sessionFactory.getCurrentSession();
    GroupMembers groupMembers = (GroupMembers) session.get(GroupMembers.class, memberId);
    if(!(groupMembers == null)){
        groupMembers.getGroupAccounts().clear();
        session.flush();
        session.delete(groupMembers);
        return true;
    } else {
        return false;
    }
}

GroupAccount实体：

@Entity
@Table(name="groupaccount")
public class GroupAccount {
 @Id
    @Column(name="groupid")
    @GeneratedValue(strategy = GenerationType.SEQUENCE,generator = "groupaccount_seq_gen")
    @SequenceGenerator(name = "groupaccount_seq_gen",sequenceName = "groupaccount_seq")
    private Long groupId;
 @ManyToMany(cascade = CascadeType.ALL)
    @JoinTable(name = "memberjunction", joinColumns = {@JoinColumn(name = "groupid")},
                inverseJoinColumns = {@JoinColumn(name = "memberid")})
    private Set<GroupMembers> groupMembersSet = new HashSet<>();
    public void setGroupMembersSet(Set<GroupMembers> groupMembersSet){
        this.groupMembersSet = groupMembersSet;
    }
    public Set<GroupMembers> getGroupMembersSet(){
        return this.groupMembersSet;
    }
}

GroupMembers实体：

@Entity
@Table(name="groupmembers")
public class GroupMembers {
 @Id
    @Column(name="memberid")
    @GeneratedValue(strategy = GenerationType.SEQUENCE,generator = "groupmembers_seq_gen")
    @SequenceGenerator(name = "groupmembers_seq_gen",sequenceName = "groupmembers_seq")
    private int memberid;
 @ManyToMany(mappedBy = "groupMembersSet")
    private Set<GroupAccount> groupAccounts = new HashSet<>();
    public void setGroupAccounts(Set<GroupAccount> groupAccounts){
        this.groupAccounts = groupAccounts;
    }
    public Set<GroupAccount> getGroupAccounts(){
        return this.groupAccounts;
    }
}

最新错误日志：

org.postgresql.util.PSQLException: ERROR: update or delete on table "groupmembers" violates foreign key constraint "groupmembers_memberjunction_fk" on table "memberjunction"
  Detail: Key (memberid)=(2501) is still referenced from table "memberjunction".
    org.postgresql.core.v3.QueryExecutorImpl.receiveErrorResponse(QueryExecutorImpl.java:2198)
    org.postgresql.core.v3.QueryExecutorImpl.processResults(QueryExecutorImpl.java:1927)

上面的方法失败了，正如它所说的，有一个对memberJunction的引用。如何查询memberJunction并删除与memberId对应的条目。任何帮助都会很好。非常感谢..：-）

Answer 1

您需要执行以下操作：

for(GroupAccount groupAccount : groupMembers.getGroupAccounts()) {
    groupAccount.getGroupMembersSet().remove(this);
}
groupMembers.getGroupAccounts().clear();
session.flush();
session.delete(groupMembers);

因为您有@ManyToMany关联，所以关联表在运行时不可用。为此，您可以：

1. 删除GroupMembers之前，请从GroupMembers中清除GroupAccounts。请确保刷新，以确保删除操作不会阻止对可删除实体状态的更新。

2. 您可以将@ManyToMany替换为与MemberJunction实体（其PK/@Id是从GroupMembers和GroupAccount构建的）的@OneToMany关联。通过这种方式，您可以将删除从GroupMembers级联到MemberJunction mappedBy集合，因为它将删除关联表行，而不是实际的GroupAccount实体。