Grails GORM/HQL - retrieve data from association

I have a Blog domain class, which has many messages:

class B开发者_如何学Golog {

    String description

    static hasMany = [messages : Message]
    static belongsTo = [owner : User]

    static constraints = {
        description blank: true, nullable: true
    }
}

class Message {

    String content
    String title
    User author

    Date dateCreated
    Date lastUpdated

    static hasMany = [comments : Comment]

    static constraints = {
        content blank: false
        author nullable: false
        title nullable: false, blank: false
    }

    static mapping = {
        content type: "text"
        sort dateCreated: 'desc'
    }
}

Message is used also in other places of the application, so association is unidirectional. How can I get 20 latest blog messages, ordered by creation date? By latest blog messages, I mean 20 latest messages which are associated with ANY blog.

class Blog {
    ...
    ...
    static hasMany [messages: BlogMessages]
    ...
    ...
}

class Message {
    ...
    // exactly like you have it
    ...
}

class BlogMessage extends Message {
    Blog blog
}

Then you can fetch like this...

BlogMessage.list([max:20])

def latestMessages = Message.listOrderByDateCreated(max:20, order:"desc")