20130517-Grails In Action-5、控制应用程序流(02小节)

service：让程序更健壮和可维护

1、实现PostService

grails create-service com.grailsinaction.post

package com.grailsinaction

class PostService {
    /*如果发生错误，数据库回滚*/
    boolean transactional = true

    Post createPost(String userId, String content) {
        def user = User.findByUserId(userId)
        if (user) {
            def post = new Post(content: content)
            user.addToPosts(post)
            if (user.save()) {
                return post
            } else {
                throw new PostException(message: "Invalid or empty post", post: post)
            }
        }
        throw new PostException(message: "Invalid User Id")
    }
}

class PostException extends RuntimeException {
    String message
    Post post
}

2、修改PostController，引入PostService，改写addPost闭包

package com.grailsinaction

class PostController {
    
    def postService

......
    
    def addPost = {
        try {
            def newPost = postService.createPost(params.id,    params.content)
            flash.message = "Added new post: ${newPost.content}"
        } catch (PostException pe) {
            flash.message = pe.message
        }
        redirect(action: 'timeline', id: params.id)
    }
}