[OPENJPA-2546] OpenJPA using ManyToMany does not work with Set<xxx>

• Type: Bug
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Affects Version/s: 2.4.0
• Component/s: instrumentation, jpa
• Labels: @ManyToMany bidirectional
• Environment: Running as part of TomEE 1.7.1
• Assignee: Unassigned
• Reporter: Jo Desmet
• Created: 24/Nov/14 09:22
• Updated: 18/Jun/15 13:22

Description

Copying my own posting from StackOverflow.com

I have two Entities User and Group, having a many to many relationship. Group manages the relationship. So in Group I have:

@Entity 
@Table(name = "GROUPS", catalog = "", schema = "GROUPADMIN")
public class Group {
  ...
  @ManyToMany
  @JoinTable(
    name = "GROUP_USERS",
    joinColumns = {@JoinColumn(name = "GROUP_ID")},
    inverseJoinColumns = {@JoinColumn(name = "USER_ID")}
  )
  private Set<User> users;

Then for User I create the entity something as follows:

@Entity 
@Table(name = "USERS", catalog = "", schema = "GROUPADMIN")
public class User {
  ...
  @ManyToMany(mappedBy="users")
  private Set<Group> groups;

Then in my backing bean, actually a @Named("registry"), I store a reference to a retrieved user as a property with the same name.

Then I use that backing bean royally in my JSF

Hello <h:outputLabel value="#{registry.user.firstName}"/>
<h:panelGroup>
  <h:dataTable value="#{registry.user.groups}" var="g">
    <f:facet name="header">Properties List</f:facet>
    <h:column>
      <f:facet name="header">Group</f:facet>
      <h:outputText value="#{g.id}"/>
    </h:column>
  </h:dataTable>
</h:panelGroup>

For those interested in the tables:

create table "GROUPADMIN".GROUPS
(
  ID VARCHAR(15) not null primary key
);
create table "GROUPADMIN".USERS
(
  ID VARCHAR(50) not null primary key,
  PASSWORD VARCHAR(50),
  FIRST_NAME VARCHAR(50),
  LAST_NAME VARCHAR(50)
);
create table "GROUPADMIN".GROUP_USERS
(
  GROUP_ID VARCHAR(15) not null,
  USER_ID VARCHAR(50) not null,
  primary key (GROUP_ID, USER_ID)
);

Depending on how (lazy vs Eager) and when I run it, the result would be always wrong, but sometimes different:

• sometimes complaining that property 'id' does not exist, like example below,
• sometimes the returned set was Empty (not null, but zero size).

Caused by:
javax.el.PropertyNotFoundException - Property 'id' not found on type org.apache.openjpa.util.java$util$HashSet$proxy
at javax.el.BeanELResolver$BeanProperties.get(BeanELResolver.java:266)

So me being curious what I actually got into that g attribute I got from the <h:dataTable>, I tried to output it simply using

<h:outputText value="#{g}"/>

What g printed out was not just one element out of the Set<Group>, but was actually the collection itself, which matches the earlier shown exception ...

One important clue is that the problem is resolved once I replace the datatype from Set<Xxx> to List<Xxx>. With that change, everything started working as expected.

However Logically wise I do need it as a Set, and the JSR documentation seems to support that.