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POProblem with equals() method in Hibernate
 

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    <p>I am developing an application in Hibernate where I have model classes like these:</p> <pre><code>public class Employee { private int ID; private String name; private Department department; //other properties //constructors, getters and setters } </code></pre> <p>Note that the <code>ID</code> is not a value populated by the user and is populated using <code>GenerationType.Identity</code> as the <code>strategy</code>.</p> <p>Also I have another class <code>Department</code> as follows:</p> <pre><code>public class Department { private int ID; private String name; private Set&lt;Employee&gt; employees; //this is actually a HashSet //other implementations } </code></pre> <p>There is a <code>ManyToOne</code> bi-directional relationship between an <code>Employee</code> and a <code>Department</code>.</p> <p>So to add a new <code>Employee</code> to an existing <code>Department</code>, I do the following</p> <pre><code>Department existingDepartment = ...; Employee newEmployee = ...; existingDepartment.addEmployee(newEmployee); employee.setDepartent(existinDepartment); session.save(newEmployee); </code></pre> <p>Now conceptually two <code>Employee</code> objects are the same if they have the same <code>ID</code>. So my <code>equals()</code> method in the <code>Employee</code> class looks like this:</p> <pre><code>public boolean equals(Object o) { if(!(o instanceOf Employee)) { return false; } Employee other = (Employee)o; if(this.ID == o.etID()) { return true; } return false; } </code></pre> <p>Now the problem is when I create a <code>new Employee();</code> I do not have its <code>ID</code>, since it will be assigned when it will be persisted. So when I say </p> <pre><code>existingDepartment.addEmployee(newEmployee); </code></pre> <p>the internal <code>HashSet</code> of the <code>Department</code> object is effectively using an <code>equals()</code> method which is broken [since it uses a member variable to determine equality that as not been initialized properly].</p> <p>This seems like a very basic problem but, how do I solve it? Or am I designing my classes totally wrong? Or should my <code>equals</code> method be re-written to compare other values instead of <code>ID</code>, which I guess would be absurd.</p>
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