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POHow to handle bidirectional relationships when constructing hibernate entities?
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  1. POHow to handle bidirectional relationships when constructing hibernate entities?
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    copied!<p>I want to model the relationship between two entities, a group and an account with JPA/Hibernate. An account can have several groups, but not vice versa, so we have a OneToMany relationship between account and group. My working colleague suggested to model the entities <code>Account</code> and <code>Group</code> like</p> <pre><code>public class Account { private List&lt;Group&gt; groups = new ArrayList&lt;Group&gt;(); public Account() {} public void setGroups(List&lt;Group&gt; usergroups) { this.groups = groups; } @OneToMany(mappedBy = "account") public List&lt;Group&gt; getGroups() { return groups; } } </code></pre> <p>and</p> <pre><code>public class Group { private String name; private Account account; public Group() {} public Group(String name, Account account) { this.name = name; addToAccount(account); } public void addToAccount(Account account) { setAccount(account); List&lt;Group&gt; accountGroups = account.getGroups(); accountGroups.add(this); } @ManyToOne public Account getAccount() { return account; } public void setAccount(Account account) { this.account = account; } } </code></pre> <p>My question is now about the usage of the helper method <code>addToAccount</code> in the constructor of <code>Group</code>. According to my working colleague this method is necessary because we need to update the bidirectional relationship between the two entities from both sides to ensure a consistent memory model of the two entities.</p> <p>However I believe calling the method <code>addToAccount</code> in the constructor is not a good idea, because</p> <ol> <li><p>The <code>List</code> of <code>Group</code>s is lazily fetched, so calling the method <code>addToAccount</code> needs an open transaction. So the constructor of <code>Group</code> can only be called inside an open transaction. In my opinion this is a very annoying restriction.</p></li> <li><p>The <code>Account</code> object given as argument to the constructor of <code>Group</code> is changed by the constructor. In my opinion, this is an surprising side effect of the <code>Group</code> constructor and should not happen.</p></li> </ol> <p>My suggestion was to better use a simple constructor like</p> <pre><code> public Group(String name, Account account) { this.name = name; this.account = account; } </code></pre> <p>and deal with the bidirectional relationship manually. But maybe I'm wrong. Is there a common way how one should handle bidirectional relationships when constructing hibernate entities?</p>
 

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