grails - Grails GORM/HQL-从关联中检索数据

Question

我有一个Blog域类，其中包含许多消息:

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'
    }
}

消息还在应用程序的其他地方使用，因此关联是单向的。如何获得20条最新博客消息(按创建日期排序)？所谓最新博客消息，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，您可以像这样获取...

BlogMessage.list([max:20])