Question

I would like to create a grails domain class that links to itself.

This related post suggests a solution but I can’t get it to work: Grails domain class relationship to itself

For one thing I don’t understand what comparable does and would need to add a int compareTo(obj) method.

Adding the following to my code without implementing Comparable compiles, but grails crashes at runtime:

//NavMenu parent
SortedSet subItems
static hasMany = [subItems: NavMenu]
static belongsTo = [parent: NavMenu]
static constraints = { parent(nullable:true) }

Thanks in advance

Answer 1

When you’re using SortedSet, a sort algorithm is internally executed, but it needs a sort criteria. You need to implement the Comparable interface because that is the standard way to provide a sort criteria to the internal algorithm.

If you don’t need a specific order, you can delete the SortedSet subItems line and thus avoid implementing the Comparable interface.