Dynamic finders with Grails many-to-many relationship -

i have 2 domain classes mapped many-to-many relationship. followed instruction of grails documentation, still have problem when processing data on domains. here 2 domain classes:

class user {     string name     int age     string job     static hasmany = [groups : group]     static belongsto = [org : organization] }  class group {     string groupname     string code     static hasmany = [members : user] } 

my problems are:
1. above relationship require 1 class hold belongsto "owner" of relationship. in context, user belongs group, not know how put belongsto user class, because standard syntax grails suggest static belongsto = [group] (just specify owner class name), cannot:
- put exist belongsto this: static belongsto = [org : organization, group]
- or define belongsto this: static belongsto = [group]

2. is below example right:

   class book { string title static belongsto = author static hasmany = [authors:author]

   static mapping = {     authors jointable:[name:"mm_author_books", key:'mm_book_id' ] } 

   } class author { string name static hasmany = [books:book]

   static mapping = {     books jointable:[name:"mm_author_books", key:'mm_author_id'] } 

   }

(ref link: many-to-many link tables in grails (gorm) / hibernate)
mean need specify name of foreign key of join table each class?

3. if want find user members of specified group name "abc", how can use dynamicfinder of grails?

thank much

it rare m2m relationships have owning side, i've found odd have specify 1 gorm work correctly. because of this, don't way. create join table domain. things really simple.

class usergroup implements serializable {      user user     group group      boolean equals(other) {         if (!(other instanceof usergroup)) {             return false         }          other.user?.id == user?.id &&             other.group?.id == group?.id     }      int hashcode() {         def builder = new hashcodebuilder()         if (user) builder.append(user.id)         if (group) builder.append(group.id)         builder.tohashcode()     }      static usergroup get(long userid, long groupid) {         find 'from usergroup user.id=:userid , group.id=:groupid',             [userid: userid, groupid: groupid]     }      static usergroup create(user user, group group, boolean flush = false) {         new usergroup(user: user, group: group).save(flush: flush, insert: true)     }      static boolean remove(user user, group group, boolean flush = false) {         usergroup instance = usergroup.findbyuserandgroup(user, group)         instance ? instance.delete(flush: flush) : false     }      static void removeall(user user) {         executeupdate 'delete usergroup user=:user', [user: user]     }      static void removeall(group group) {         executeupdate 'delete usergroup group=:group', [group: group]     }      static mapping = {         id composite: ['group', 'user']         version false     } } 

then need create getters in user , group class. won't have user user or group group in either class. there no need map them hasmany/belongsto because create join table, you've done creating usergroup domain.

class user {    set<group> getgroups() {     usergroup.findallbyuser(this).collect { it.group } set   } }  class group {   set<user> getusers() {     usergroup.findallbygroup(this).collect { it.user } set   } } 

once have these in place can use methods created in usergroup domain and/or can use finders on it...

def usergroupinstance = usergroup.findbyuserandgroup(userinstance, groupinstance) def usergroups = usergroup.findallbyuser(userinstance) def usergroupinstance = usergroup.get(userid, groupid) 

you idea. presentation burt beckwith sheds more light on why approach along other great tips performance increases.