Grails GORM/HQL - 从关联中检索数据

Question

我有一个 Blog 域类，其中有许多消息：

class Blog {

    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'
    }
}

消息也在应用程序的其他地方使用，因此关联是单向的。如何获取按创建日期排序的 20 条最新博客消息？我所说的最新博客消息是指与任何博客相关的 20 条最新消息。

Answer 1

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

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

class BlogMessage extends Message {
    Blog blog
}

然后你可以像这样获取...

BlogMessage.list([max:20])

Answer 2

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