Programming

When working with automatic id's in Grails, sequence generation uses a less than useful default sequence name of hibernate_sequence. Use the following syntax as part of the GORM mapping to set the sequence name to something sane:

static mapping = {
    id generator:sequence,params:[name:'mytable_id_seq']
}

Working on a Spring application using Hibernate recently I encountered the dreaded org.hibernate.HibernateException: Illegal attempt to associate a collection with two open sessions error. Fixes for this vary widely; it can be caused by problems ranging from bad session handling in your framework configuration, bad cascade settings, incorrect persistence settings, to forgetting initialization of an array stored in a @ManyToOne database relation.

Make sure to check thoroughly for the latter before wasting hours changing the transaction handling, trying various cascade settings, or mucking with persistence annotations.