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    <p>Bauer and King's book <em>Java Persistence with Hibernate</em> advises against using the key field for equals and hashCode. They advise you should pick out what would be the object's business key fields (if there was no artificial key) and use those to test equality. So in this case if role name was not a necessary field you would find the fields that were necessary and use them in combination. In the case of the code you post where rolename is all you have besides the id, rolename would be what I'd go with.</p> <p>Here's a quote from page 398:</p> <blockquote> <p>We argue that essentially every entity class should have <em>some</em> business key, even if it includes all properties of the class (this would be appropriate for some immutable classes). The business key is what the user things of as uniquely identifying a particular record, whereas the surrogate key is what the application and database use.</p> <p><em>Business key equality</em> means that the equals() method compares only the properties that form the business key. This is a perfect solution that avoids all the problems presented earlier. The only downside is that it requires extra thought to identify the correct business key in the first place. This effort is required anyway; it's important to identify any unique keys if your database must ensure data integrity via constraint checking.</p> </blockquote> <p>An easy way I use to construct an equals and hashcode method is to create a toString method that returns the values of the 'business key' fields, then use that in the equals() and hashCode() methods. CLARIFICATION: This is a lazy approach for when I am not concerned about performance (for instance, in rinky-dink internal webapps), if performance is expected to be an issue then write the methods yourself or use your IDE's code generation facilities. </p>
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    1. POWhat is the correct way of overriding hashCode () and equals () methods of persistent entity?
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    1. USNathan Hughes
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    1. POWhat is the correct way of overriding hashCode () and equals () methods of persistent entity?
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    1. COSidenote out of experience with large volume data: using String concatenation (or any non-primitive calculation) within hashCode() or equals() will result in severe, nearly non-traceable performance impacts, esp. if the object are kept in large collections. Reflective EqualsBuilders/HashCodeBuilders or using toString() is not advisable. Better to use IDE-generated hashCode() methods like Eclipse does it for the business fields.
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    2. COHow big does a collection have to grow for that to become a real issue?
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    3. CO@Nathan, your method needn't be as poorly performing as you fear, if you cache the result of toString and hashCode. Of course that's easier if your class is immutable, but it's manageable even if the class is mutable.
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