Hi,
I am pretty new to Hibernate, I tried the tutorial and looked for documentation, and I have to ask something related on how to define in the OO model the equivalent concept of unique contraints in the relational model, so that I don't risk to have duplicate insertion for newly instanted objects that are "equal" on some fields.

So:

1) I am using Annotations to define the mapping, and I would like to define the equivalent relational unique constraint on N properties of one of my given domain objects, since the key is the surrogate Long id field. Can someone give me a hint on how to do that or point me some reference documentation? I only found how to do that with the mapping in xml.

2) Assuming I did all at point (1), is that just enough to prevent me from inserting duplicate "equivalent" objects into the database or I have also to ovveride equals() (and hashCode() ) to follow the natural key ? (I think it would be reasonable to do so)

Thanks a lot,
Alessio Pace.

1) You can define a unique constraint with @Column( unique=true )... There are also constraint annotations (Annotations Reference Guide Chapter 3) but there are none that annotate 'Unique'.

2) From what I understand, Hibernate does not use hashCode and equals when inserting records in a database ( see http://www.hibernate.org/109.html ). Hibernate looks at what you have listed as an id and checks if that is already in the table, if not then it will add it.

If you have a composite primary key set or if you make a column unique in your table schema then Hibernate will throw an Exception and not insert the record if it is violated. You can catch this Exception and deal with it however you would like.

-B
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I found a solution for my multi-column unique constraint like this:




So that I can declare the multi-column uinque constraint all together, and not per-column.

Thanks for your help,
Alessio Pace