grails - 创建一个标准主题

Question

使用grails创建网络论坛时遇到一些问题。在我的Controller中，我需要为网站工作创建一个标准主题，我使用的是教程代码。所以我的问题是:如何创建标准主题以使此代码起作用？

我需要创建的部分在第11行。

Controller :

class ForumController {
def springSecurityService

def home() {
    [sections:Section.listOrderByTitle()]
}

def topic(long topicId) {
    Topic topic = Topic.get(topicId)

    if (topic == null){


    }


    params.max = 10
    params.sort = 'createDate'
    params.order = 'desc'

    [threads:DiscussionThread.findAllByTopic(topic, params),
     numberOfThreads:DiscussionThread.countByTopic(topic), topic:topic]
}

def thread(long threadId) {
    DiscussionThread thread = DiscussionThread.get(threadId)

    params.max = 10
    params.sort = 'createDate'
    params.order = 'asc'

    [comments:Comment.findAllByThread(thread, params),
     numberOfComments:Comment.countByThread(thread), thread:thread]

}


@Secured(['ROLE_USER'])
def postReply(long threadId, String body) {
    def offset = params.offset
    if (body != null && body.trim().length() > 0) {
        DiscussionThread thread = DiscussionThread.get(threadId)
        def commentBy = springSecurityService.currentUser
        new Comment(thread:thread, commentBy:commentBy, body:body).save()

        // go to last page so user can view his comment
        def numberOfComments = Comment.countByThread(thread)
        def lastPageCount = numberOfComments % 10 == 0 ? 10 : numberOfComments % 10
        offset = numberOfComments - lastPageCount
    }
    redirect(action:'thread', params:[threadId:threadId, offset:offset])
}
}

Answer 1

当前，您正在尝试首先查找与提供的topicId对应的Topic域类的实例，然后检查该主题是否为空。

这是一个问题，好像topicId为null，查找将失败并抛出null指针异常。

要解决此问题，您只需将查询包装在if-null检查中，如下所示，以确保您实际上具有有效的topicId。

您的其他问题(如何实际设置默认值)更加直观。如果未找到任何主题，只需使用默认的默认构造函数创建一个主题，或向该构造函数提供key:value对。 [请参见下面的代码以获取示例]。有关Grails对象关系映射系统的更多信息，请查看their documentation。

def topic(long topicId) {
    Topic topic

    /* If you have a valid topicId perform a lookup. */
    if (topicId != null){
        topic = Topic.get(topicId)
    }

    /* If the topic hasn't been set correctly, create one with default values. */
    if (topic == null) {
        topic = new Topic()
       /* You may want to have a look at the grails docs to see how this works. */
        toipic = new Topic(name: "Default", priority: "Highest")
    }

    params.max = 10
    params.sort = 'createDate'
    params.order = 'desc'

    [threads:DiscussionThread.findAllByTopic(topic, params),
     numberOfThreads:DiscussionThread.countByTopic(topic), topic:topic]
}