[jboss-user] [EJB 3.0] - How to store information about many-to-many relationship its
I have a situation where I have a many-to-many bidirectional relationship between two
entity beans "User" and "Group", where users can belong to many groups
and groups can have many users. I want to keep track of the status of the relationship
itself and still take advantage of automatic table generation from source annotations in a
database-independent fashion. For example, a user's status in a group could be
"invited" or "member" independently for each group that the user is
related to. The user is the owning side of the relation, although that doesn't seem
relevant to me. It seems to me that what I want to do is have another column in the join
table and I'm stumped about how to do in a clean way and was unable to find anything
about this topic; I've read Bill Burke's O'Reilly EJB3 book and couldn't
think of good search terms that would capture this issue. (I'm also using Seam,
although I don't think that's germane here.) I imagine I could hack in another
column to the join table with an ALTER TABLE, but that strikes me as a kluge and I
don't see how I could easily deal with group member status using EJB3. Does anybody
have a suggestion? Pointers on how to do this or to previous discussions of this topic
gratefully accepted.
current Group.java
| ...
| @Entity
| @Table(name="GROUPS")
| public class Group implements Serializable {
|
| private long id;
| private Set<User> users = new HashSet<User>();
|
| @Id
| @Column(name="GROUP_ID")
| @GeneratedValue
| public Long getId() {
| return id;
| }
| public void setId(Long id) {
| this.id = id;
| }
|
| @ManyToMany(cascade=CascadeType.PERSIST,mappedBy="groups")
| public Set<User> getUsers() {
| return users;
| }
| public void setUsers( Set<User> users ) {
| this.users = users;
| }
|
| ...
| }
|
current User.java
| ...
| @Entity
| @Table(name="USERS")
| public class User implements Serializable {
|
| private long id;
| private Set<Group> groups = new HashSet<Group>();
|
| @Id
| @Column(name="USER_ID")
| @GeneratedValue
| public Long getId() {
| return id;
| }
| public void setId(Long id) {
| this.id = id;
| }
|
| @ManyToMany(cascade=CascadeType.PERSIST)
| @JoinTable(name="USER_GROUP",
| joinColumns={@JoinColumn(name="USER_ID")},
| inverseJoinColumns={@JoinColumn(name="GROUP_ID")})
| public Set<Group> getGroups() {
| return groups;
| }
| public void setGroups( Set<Group> groups ) {
| this.groups = groups;
| }
|
| ...
| }
|
currently generated schema:
anonymous wrote :
| 2006-07-27 19:15:53,790 DEBUG [org.hibernate.tool.hbm2ddl.SchemaExport] create table
GROUPS (GROUP_ID bigint generated by default as identity (start with 1), ..., primary key
(GROUP_ID))
| 2006-07-27 19:15:53,790 DEBUG [org.hibernate.tool.hbm2ddl.SchemaExport] create table
USERS (USER_ID bigint generated by default as identity (start with 1), ..., primary key
(USER_ID))
| 2006-07-27 19:15:53,790 DEBUG [org.hibernate.tool.hbm2ddl.SchemaExport] create table
USER_GROUP (USER_ID bigint not null, GROUP_ID bigint not null, primary key (USER_ID,
GROUP_ID))
| 2006-07-27 19:15:53,790 DEBUG [org.hibernate.tool.hbm2ddl.SchemaExport] alter table
USER_GROUP add constraint FKC62E00EB21CA0D09 foreign key (USER_ID) references USERS
| 2006-07-27 19:15:53,790 DEBUG [org.hibernate.tool.hbm2ddl.SchemaExport] alter table
USER_GROUP add constraint FKC62E00EB44BDA00B foreign key (GROUP_ID) references GROUPS
|
|
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