Java / Hibernate / Reverse Engineering / @GeneratedValue

RBX · 10-11-2012 06:42PM #1

Hello

I'm having a few problems with Hibernate, and I'm hoping someone can help me spread some light on it.

I've created a database table ( in PostgreSQL ), which has an automatically incrementing ( using a sequence ) primary key. In Netbeans ( v7.2.1 ), I created an annotated class to map to this table, which has methods corresponding to each column. The primary key has the @Id annotation, but doesn't have a @GeneratedValue type one.

This means that whenever I try to insert a row using this class, that I cannot do so without specifying value for the id column.

Adding the annotation @GeneratedValue(strategy= GenerationType.IDENTITY) manually allows me to use this, but in the longer term, I'll be making several changes as time goes on to these tables, and I really don't want to be manually adding that annotation every time.

During the past 3 days searching, I've tried adding sections to the hibernate.reveng.xml file that was generated. This didn't help.

  <table name="table_name">
      <primary-key>
          <generator class="identity" />
          <key-column name="id" />
      </primary-key>
  </table>

Another thing that uncle Google surfaced up, was creating a custom Reverse Engineering strategy, but I can find very little in terms of documentation on how to do that.

I'd appreciate any pointers anyone would have in the right direction.

Disclosure: This is part of a college assignment, but not one directly related to hibernate. The project is to build a service, and Hibernate is a tool chosen to assist with data persistence.

Also: I may be missing something very obvious here to seasoned java developers - I've only been using Java for about a month - I spend the rest of my life so far as a sysadmin with higher level languages ( Perl, Python, etc )

Giblet · 10-11-2012 08:42PM

Postgres uses sequences which have to be created manually and you should assign "sequence" and pass the name of the sequence.

<generator class="sequence">
                <param name="sequence">sequence name</param>
        </generator>

RBX · 10-11-2012 09:11PM

Giblet wrote: »

<generator class="sequence">
                <param name="sequence">sequence name</param>
        </generator>

Thanks Giblet - I just tried that, but it's not having the desired effect. I'm still not getting any @GeneratedValue like annotations.

Incase I'm missing something silly, here's my full hibernate.reveng.xml as it now stands:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-reverse-engineering PUBLIC "-//Hibernate/Hibernate Reverse Engineering DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-reverse-engineering-3.0.dtd">
<hibernate-reverse-engineering>
  <schema-selection match-catalog="ressys"/>
 

  
  <table name="legs" schema="ressys" class="Legs">
      <primary-key>
          <generator class="sequence">
              <param name="sequence">legs_id_seq</param>
          </generator>
          <key-column name="id" />
      </primary-key>
  </table>
 
</hibernate-reverse-engineering>

RBX · 12-11-2012 01:31PM

Ok - it seems this is somehow related to the use of PostgreSQL; probably in one of the hibernate/jdbc drivers used to generate the code.

I tried the same exercise in MySQL, and the @GeneratedValue is inserted as expected.

I now need to figure out if I'm missing something in my PostgreSQL table to let hibernate know that this should have a @GeneratedValue annotation.

RBX · 24-11-2012 01:51AM

For my use case, I worked around the problem in this case by switching to MySQL. This was feasible in this case since I'm time bound, and it's not a course in databases. I just documented in my writeup that if Hibernate, PostgreSQL, and reverse Engineering worked correctly, then I would have used the constraint features available in PostgreSQL, and how I'd have used them.

Thanks anyway for the pointer Giblet.

I guess the only thing remaining in this thread is changing [Question] to [WorkedAround] or [Solved] or something.

Java / Hibernate / Reverse Engineering / @GeneratedValue

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