Usually I'm using One-to-many relationship by this way :

class Subject {
    static hasMany = [ crfs : Crf ]
    String name 
    ...
} 

class Crf { 
String title
String info 
...
} 

I can extend this relationship to others domains, Ex :

static hasMany = [ crfs : Crf, crfb : CrfBlood ...]

But in my case I have to link the Subject domain to 30 others domains, maybe more...(ex : CrfBlood, CrfMedical, crfFamily, etc...).

What domain model implementation should I use in my case ?
I would like to keep the dynamic finders usability in my project.