In part 1 of this series, I introduced you to some of the subtleties associated with persisting domain instances with GORM. This time, I’m going to tackle relationships with particular focus on hasMany and belongsTo.
GORM provides only a few basic elements for defining relationships between domain classes, but they are sufficient to describe most needs. When I give training courses on Grails, it always surprises me how few slides cover relationships. As you can imagine, this apparent simplicity does hide some subtle behaviour that can trip up the unwary. Let’s start with the most basic of relationships: the many-to-one.