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POSpring + JPA many to many relationship
 

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  1. POSpring + JPA many to many relationship
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    <p>I'm very new to Spring and I'm trying to make a many-to-many relationship work as I expect. The relationships works fine, the tables are created and the data is inserted correctly. What I expect, is that when I empty a List (i.e. I empty the ArrayList "users" from an object of type "Group"), I expect the system to remove the relationships from the database - but it doesn't.</p> <p>I have the following classes:</p> <pre><code>@Entity @Table(name = "`group`") public class Group { @Id @GeneratedValue @Column(name = "id") private int id; @Column(name = "name") private String name; @ManyToMany(cascade = {CascadeType.ALL}) @JoinTable( name = "`user_has_group`", joinColumns = @JoinColumn(name = "group_id", referencedColumnName = "id"), inverseJoinColumns = @JoinColumn(name = "user_id", referencedColumnName = "id") ) private List&lt;User&gt; users = new ArrayList&lt;User&gt;(); ... } @Entity @Table(name = "`user`") public class User { @Id @GeneratedValue @Column(name = "id") private int id; @Column(name = "name") private String name; @ManyToMany(mappedBy = "users") private List&lt;Group&gt; groups = new ArrayList&lt;Group&gt;(); ... } </code></pre> <p>Here are the DAOs:</p> <pre><code>@Repository public class GroupJpaDao implements GroupDao { private EntityManager em; @Transactional public void save(Group group) { this.em.merge(group); } ... @PersistenceContext void setEntityManager(EntityManager entityManager) { this.em = entityManager; } } @Repository public class UserJpaDao implements UserDao { private EntityManager em; @Transactional public void save(User user) { this.em.merge(user); } ... @PersistenceContext void setEntityManager(EntityManager entityManager) { this.em = entityManager; } } </code></pre> <p>Here is the test method:</p> <pre><code>@Test public void test() { Group g = new Group(); g.setName("Test group"); groupDao.save(g); // Works fine - inserts the group into the database User u = new User(); u.setName("Test user"); userDao.save(u); // Works fine - inserts the user into the database g.addUser(u); groupDao.save(g); // Works fine - adds the many-to-many relationship into the database g.removeAllUsers(); groupDao.save(g); // Doesn't work - I'm expecting it to remove all the related relationships from the database but it doesn't! } </code></pre> <p>Am I doing something wrong or is it something not possible to do?</p> <p>Any hint is really appreciated.</p> <p>Thank you!</p>
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    1. USsatoshi
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    1. COdid you try adding `delete-orphan` to your cascade `attribute`?
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    2. CODid you declared `IdTransferringMergeEventListener`?
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    3. CODon't know if that's the cause of the problem, but the save method shouldn't return void. It should return the result of the merge call. Try doing this change and using the returned group : `g = groupDao.save(g);`
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      1. USJB Nizet
 

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Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

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