回调，返回值和HTML5的executeSql函数

问题描述

我有一个大问题。我知道这是关于回调，闭包，但我不知道如何解决问题。这是我的代码

I have a big problem. I know it's about callback, closure but I don't know how to solve the problem. Here is my code

$.Model.extend('Article',
{
     findAll : function(params, success, error){                
                var result = []
                db.transaction(function(tx) {
                    tx.executeSql('select * from contents', [],function(tx, rs) {
                        for(var i=0; i<rs.rows.length; i++) {
                            var row = rs.rows.item(i)
                            result[i] = {
                                id: row['id'],
                                title: row['title'],
                                body: row['body']
                            }
                        }
                    })
                })
                //here result is undefined
                alert(result)
                return result
    }
})
//undefined
var view = Article.findAll

我知道executeSql是异步函数，但我不知道如何保存并返回executeSql的结果。我使用javascript mvc和HTML离线数据库。

I know that executeSql is asynchronous function, but I don't know how to save and return result of executeSql. I use javascript mvc and HTML offline database.

感谢您的帮助

推荐答案

W3C Web数据库规范讨论了对异步和同步数据库操作的支持。

The W3C web database spec talks about support for both Asynchronous and Synchronous database operations. (See 4.3 and 4.4)

如果你不能使用同步实现，那么你可能想考虑这样的问题：

If you can't use a synchronous implementation, then you might want to consider approaching the problem like this instead:

$.Model.extend('Article',
{
     findAll : function(params, success, error){                
                var result = []
                db.transaction(function(tx) {
                    tx.executeSql('select * from contents', [],function(tx, rs) {
                        for(var i=0; i<rs.rows.length; i++) {
                            var row = rs.rows.item(i)
                            result[i] = {
                                id: row['id'],
                                title: row['title'],
                                body: row['body']
                            }
                        }

                        success(result); //toss the result into the 'success' callback
                    })
                })
                //here result is undefined
                alert(result)
                return result
    }
})

Article.findAll([], function(view) {
        //...
    }, function() {
        //error occured
    });

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