如何刷新:真的不同于手动刷新currentSession？

我有一个GORM对象,我正在进行集成测试.它有一个beforeUpdate钩子,可以保存以前密码哈希的历史记录.代码看起来像这样:

class Credentials {
    List passwordHistory = []
    String username
    String password

    static hasMany = [passwordHistory : String]

    def beforeUpdate() {
        // of course I'm not really storing plain-text passwords, but
        // this is just for illustration.
        if (isDirty('password')) { passwordHistory << password }
    }
}

在集成测试中,我想知道为什么:

appUser.credentials.password = newPassword
appUser.save(flush: true)
sessionFactory.currentSession.flush()
AppUser.withNewSession {
    appUser = AppUser.get(appUser.id)
    appUser.credentials.empty // eagerly fetch the list while session is open
}
assert !appUser.credentials.passwordHistory.empty() // contains the previous password

有效,但是

appUser.credentials.password = newPassword
appUser.save()
sessionFactory.currentSession.flush()
AppUser.withNewSession {
    appUser = AppUser.get(appUser.id)
    appUser.credentials.empty // eagerly fetch the list while session is open
}
assert !appUser.credentials.passwordHistory.empty() // is empty

才不是.不同之处flush: true在于appUser.save()通话中.我认为调用save()将对象附加到当前会话,但刷新当前会话不会将密码添加到passwordHistory列表中.这里到底发生了什么？