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POBest way to prevent unique constraint violations with JPA
 

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  1. POBest way to prevent unique constraint violations with JPA
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    <p>I have an <code>Keyword</code> and a <code>KeywordType</code> as entities. There are lots of keywords of few types. <br><br>When trying to persist the second keyword of a type, the unique constraint is violated and the transaction is rolled back. <br><br>Searching SO i found several possibilies (some of them from different contexts, so I'm not sure of their validity here) - <a href="https://stackoverflow.com/questions/3500096/lost-transaction-with-jpa-unique-constraint">this post</a> and <a href="https://stackoverflow.com/questions/2519902/elegantly-handling-constraint-violations-in-ejb-jpa-environment">this post</a> advise catching the Exception which would be of no use to me as I end up where I started and still need to somehow persist the keyword. <br>Same applies to locking proposed for a different situaltion <a href="https://stackoverflow.com/questions/2641732/jpa-2-0-eclipselink-check-for-unique.">here</a> <br>Custom insert statements as proposed in <a href="https://stackoverflow.com/questions/3275100/jpa-and-unique-fields">this</a> and <a href="https://stackoverflow.com/questions/913341/can-hibernate-work-with-mysqls-on-duplicate-key-update-syntax">this</a> posts wouldn't work proper I guess, since I'm using Oracle and not MySQL and woulnd like to tie the implementation to Hibernate. <br><br>A different workaround would be trying to retrieve the type first in the code generating the keywords, and set it on the keyword if found or create a new one if not.<br><br> So, what would be the best - most robust, portable (for different databases and persistence providers) and sane approach here? </p> <p>Thank you.</p> <p>The involved entities: </p> <pre><code>public class Keyword { @Id @GeneratedValue private long id; @Column(name = "VALUE") private String value; @ManyToOne @JoinColumn(name = "TYPE_ID") private KeywordType type; ... } </code></pre> <p>and</p> <pre><code>@Entity @Table(uniqueConstraints = {@UniqueConstraint(columnNames = { "TYPE" }) }) public class KeywordType { @Id @GeneratedValue private long id; @Column(name = "TYPE") private String type; ... } </code></pre>
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    1. COComing from the view layer of your application, do you know whether 'the user' is creating a new keyword type or using an existing one?
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    2. COusing existing ones which come from document analysis. would it change the solution?
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