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POHibernate @OneToMany relationship mapping
 

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    <p>I am trying to design some kind of user to user relationship, such as "user A follows user B" and "User A wants to be User B's friend".</p> <p>I have a User class, and the way it is designed looks like this:</p> <pre><code>@Entity public class User{ @OneToMany(cascade=CascadeType.ALL, fetch=FetchType.EAGER) List&lt;User&gt; followers; @OneToMany(cascade=CascadeType.ALL, fetch=FetchType.EAGER) List&lt;User&gt; following; @OneToMany(cascade=CascadeType.ALL, fetch=FetchType.EAGER) List&lt;User&gt; friendRequests; @OneToMany(cascade=CascadeType.ALL, fetch=FetchType.EAGER) List&lt;User&gt; requesting; @OneToMany(cascade=CascadeType.ALL, fetch=FetchType.EAGER) List&lt;User&gt; friends; } </code></pre> <p>I am running into two problems:</p> <ul> <li>Hibernate is giving me <strong>cannot simultaneously fetch multiple bags</strong> problem</li> <li>I have looked up online, people said to remove FetchType.EAGER or change it to Set instead of List, but that resulted me <strong>Field doesn't have a default value</strong></li> </ul> <p>I have a feeling that the relationship is not defined properly, and also I should be seeing more tables, because right now, I only see User table, and User_User table.</p> <p><hr/> <strong>Update</strong></p> <p>The following creates 3 table, friends, followers, and requesters. Is this somewhat optimized compared to 5 tables? And are there any advantage to this in comparison with what Mr.J4mes suggested?</p> <pre><code>@ManyToMany @JoinTable(name = "followers", joinColumns = @JoinColumn(name = "followerId"), inverseJoinColumns = @JoinColumn(name = "userId")) private List&lt;User&gt; followers; @ManyToMany @JoinTable(name = "followers", joinColumns = @JoinColumn(name = "userId"), inverseJoinColumns = @JoinColumn(name = "followerId")) private List&lt;User&gt; following; @ManyToMany @JoinTable(name = "friends", joinColumns = @JoinColumn(name = "userId"), inverseJoinColumns = @JoinColumn(name = "friendId")) private List&lt;User&gt; friends; @ManyToMany @JoinTable(name = "requesters", joinColumns = @JoinColumn(name = "requesterId"), inverseJoinColumns = @JoinColumn(name = "userId")) private List&lt;User&gt; friendRequests; @ManyToMany @JoinTable(name = "requesters", joinColumns = @JoinColumn(name = "userId"), inverseJoinColumns = @JoinColumn(name = "requesterId")) private List&lt;User&gt; requesting; </code></pre>
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