From: Markus Fuchs <Markus.Fuchs_at_Sun.COM>
Date: Mon, 26 Mar 2007 14:43:59 -0700

Hi Tim,

Romanowski, Tim wrote:

Tricky problem I thought I solved, and I hope someone could explain to me both 1) why this kind of works, and 2) why it doesn’t completely work.

 

Situation: I have a ManyToMany relationship between two entities, Team and User. A team has many users and a user has many teams.  I have a join table called team_users which contains two fields: teamid and username, which map to the corresponding primary keys of the Team and User tables.

 

Problem: Creating a ‘standard’ ManyToMany relationship where I pick an arbitrary owning entity and annotate a member variable (rather than its get method) does not work.  The only way for me to compile and deploy my webapp is to annotate these two entities as you see below. 

 

Questions:

1)       In the Team entity, why doest the @JoinTable annotation on the getUserCollection method work, but not work if I instead place that same annotation on the userCollection property?

Both ways should work. Please note that you can't have both field- and property-based access in the same entity (Your example shows the Id annotation on the field, and you mention annotating the getter method)

2)       In the User entity, why must I use the @AttributeOverride annotation on the teamCollection property?

No annotation besides "mappedBy" should be used on the non-owning side. The AttributeOverwrite must not be used.

Could you please send me your the Team and User classes?

Thanks,

-- markus.

3)       Why does NetBeans report “Inconsistent access type in entity class because a field in this class or its super class chain is already annotated as @Id or @EmbeddedId.”  This error is shown as a red squiggly line under getUserCollection in the Team entity.  BUT…I can still compile and deploy, and run my app.

 

Would someone please explain to me some of the details with what is going on here?  Perhaps my entire approach is backward?

I am compiling with JDK 1.5.0_11-b3 and running on Glassfish V2 Build 40.  This problem goes back to builds in the mid 20s (when I started using these entites). 

 

 

Team Entity:

<snip/>

    @Id @GeneratedValue(generator="teamid_gen")

    @Column(name = "TEAMID", nullable = false)

    private BigDecimal teamid;

           

<snip> now here’s the reference to my collection of User entities… </snip>           

    @ManyToMany   

    private java.util.Collection <com.my.persistence.entity.Users> userCollection;

 

 

<snip> and the only way for my code to compile and deploy (despite the NB error), specifying the getter like so… </snip>

   @ManyToMany

   @JoinTable(name = "team_users",

        joinColumns = {@JoinColumn(name = "teamid", referencedColumnName = "teamid")},

        inverseJoinColumns =  {@JoinColumn(name = "username", referencedColumnName = "username")})

    public java.util.Collection<com.my.persistence.entity.Users> getUserCollection() {

        return userCollection;

    }

 

    public void setUserCollection(java.util.Collection<com.my.persistence.entity.Users> userCollection) {

        this.userCollection = userCollection;

    }      

 

 

User entity:

            <snip/>

    @Id

    @Column(name = "USERNAME", nullable = false)

    private String username;

 

    @ManyToMany(mappedBy="userCollection")

    @AttributeOverride(name="teamCollection", column=@Column(name="teamid"))

    private java.util.Collection <com.my.persistence.entity.Team> teamCollection;

 

 

<snip> Nothing special is done to the getters and setter for this (arbitrarily selected) NON-owning side… </snip>

    public java.util.Collection <com.my.persistence.entity.Team> getTeamCollection() {

        return this.teamCollection;

    }

 

    public void setTeamCollection(java.util.Collection <com.my.persistence.entity.Team> teamCollection) {

        this.teamCollection = teamCollection;

    }

 

 

Tim