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1. Re: ManyToMany: Howto use
You don't have to use merge on the same object twice, this is a no op.
We aware that the user.getGroups() has to be the owner side (ie not contains mappedBy) unless you set both side.
Reread the merge API you should do something like u1 = (U) em.merge(u); and work with u1. -
2. Re: ManyToMany: Howto use
Hi Emmanuell,
it seems to work now. My entites are called "User" and "Group". It makes sence to explicitly define a different table name of hibernate will have problems with its SQL. Therefore I do@Entity
@Table(name="xgroup")
public class Group implements Serializable, Displayable {
@ManyToMany(fetch = FetchType.LAZY, cascade = { CascadeType.PERSIST,
CascadeType.MERGE }, mappedBy="users")
@AssociationTable(table = @Table(name = "user_group"), joinColumns = { @JoinColumn(name = "user_id_ref", referencedColumnName = "user_id") }, inverseJoinColumns = { @JoinColumn(name = "group_id_ref", referencedColumnName = "group_id") })
public Set<User> getUsers() {
return users;
}
and
@Entity
@Table(name = "xuser")
public class User implements Serializable, Displayable {
@ManyToMany(fetch = FetchType.EAGER, cascade = { CascadeType.PERSIST, CascadeType.REFRESH,
CascadeType.MERGE })
public Set<Group> getGroups() {
return groups;
}
Note that I define the table name "user_group". After deployment I find:mysql> show tables;
+-----------------+
| Tables_in_jboss |
+-----------------+
| user_group |
| xgroup |
| xuser |
| xuser_xgroup |
+-----------------+
And after running a JUnit-Test i find the data in the table xuser_xgroup:mysql> select * from user_group;
Empty set (0.01 sec)
mysql> select * from xuser_xgroup;
+---------------+-----------------+
| xuser_user_id | groups_group_id |
+---------------+-----------------+
| 100 | 51 |
| 101 | 51 |
| 101 | 52 |
+---------------+-----------------+
3 rows in set (0.01 sec) -
3. Re: ManyToMany: Howto use
One note: JBoss EJB 2.1 renames Tables of entities automagically if the conflict with a SQL keyword, like "user" -> "xuser" and "group" -> "xgroup"
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4. Re: ManyToMany: Howto use
hum
You should set the @AssociationTable on the owner side, ie the side not declaring the mappedBy. And the association table should be unique (ie not user_group and xuser_xgroup), otherwise it will be considered as 2 unrelated associations. -
5. Re: ManyToMany: Howto use
Hi Emanuell,
is it possible, that the owner-side of ManyToMany *must* be FetchType.EAGER? -