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grailsgrails-ormgrails-domain-class
Syam
Syam

Reputation: 575

GORM relational mapping

I have 3 domain classes User, Server, Quota and I want to map them with the following relations

Upvotes: 0

Views: 98

Answers (1)

cantoni
cantoni

Reputation: 3122

You can create a NxN relation between User and Server. However, will be necessary create a class for that relation. This is necessary because you need the attribute quota. In the standard way of a NxN relation Grails (Hibernate) doesn't create a class for it.

You'll need three classes:

User,Server,UserServer

Class UserServer {
  int quota
  static belongsTo = [user:User, server:Server]
  static constraints = {user unique: 'server'}
}

The unique constraint it's very important, because as you said, a User may have exactly one entry for each Server.

To link and unlink a User and Server you can use the following methods:

Class UserServer {
    int quota
    static belongsTo = [user:User, server:Server]
    static constraints = {user unique: 'server'}

    static PackScheme link(User user, Server server) {
        UserServer userServer = UserServer.findByUserAndServer(user, server)

        if (!userServer) {
            userServer = new UserServer()
            user.addToUserServers(userServer)
            server.addToUserServers(userServer)
            userServer.save()
        }

        return userServer
    }

    static void unlink(User user, Server server) {
        UserServer userServer = UserServer.findByUserAndServer(user, server)

        if (userServer) {
            user.removeFromUserServers(userServer)
            server.removeFromUserServers(userServer)
            userServer.delete()
        }
    }
}

Note that you need to create a hasMany relation in User and Server called userServers:UserServer.

This solution is based on this link: http://grails.org/Many-to-Many+Mapping+without+Hibernate+XML

Upvotes: 1

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