Grails: field uniqueness within domain hierarchy

Question

Assume that we have such domain hierarchy:

class Category {
...
    static hasMany = [groups: Group]
...
}

class Group {
...
    static belongsTo = [category: Category]
    static hasMany = [items: Item]
...
}

class Item {
...
    Integer value
    static belongsTo = [group: Group]
...
}

The field value in the Item class should be unique within one Category. How can we achieve this?

I tried to write a custom validator using criteria, but finally I got a "don't flush the Session after an exception occurs" Hibernate error. Is there a better way to check this constraint?

Answer 1

Hmm maybe

class Item {
    ...
    Integer value
    static belongsTo = [group: Group, category: Category]
    static constraints = {group value: 'category'}
    ...
}

Also you could add custom validator to check if parent group belongs to the same category.

Did not test it.