how can i add a integer list in grails domain class - grails

Question

I have created a domain class as given below, which contains an int and list of Integer properties.
class User {
int UserId
List<Integer> UserFriendsId
static constraints = {
}
User() {
this.UserId = 21
this.UserFriendsId=[1,2,3]
}
}
The table generated for this domain class while saving is as follows
mysql> select * from user;
+----+---------+---------------------+
| id | version | UserId |
+----+---------+---------------------+
| 1 | 0 | 21 |
| 2 | 0 | 21 |
| 3 | 0 | 21 |
+----+---------+---------------------+
3 rows in set (0.00 sec)
column for userFriendsId (ie: for list of integers) is not generated in this table user.
so how can solve this issue or can add list of integer in grails domain class.

Answer 1

The UserFriendsId List should be mapped as a GORM basic collection type and not simply be a list in the User domain class:
class User {
int userId
static hasMany = [userFriendsIds: Integer]
static mapping = {
userFriendsIds joinTable: [name: "user_id", column: "friend_id", type: Integer]
}
static constraints = {
}
User() {
}
}

Answer 2

Why not just make UserFriendsId a comma separated String?
class User {
int UserId
String UserFriendsId
static constraints = {
}
User() {
this.UserId = 21
this.UserFriendsId = "1,2,3"
}
}
Then:
for (userId in UserFriendsId.get(21).split(','))
{
println userId.toInteger()
/// Or do whatever ...
}