确定一个SQL select是否异步返回一个空集？

本文介绍了确定一个SQL select是否异步返回一个空集？的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述 这很容易吗？看来只有当结果不是空集时，handleResult方法才会被执行。 我想过的一个想法是将handleResult和handleCompletion作为对象的成员函数，有handleResult更新handleCompletion可以检查的成员变量。如果变量被设置，不为空，如果变量未设置，则为空，并可以相应地执行。 似乎过于复杂，希望有一个更好的解决方案？ 解决方案 function sql（ ）{ this.results = false; var me = this; this.handleResult = function（aResultSet）{ for（var row = aResultSet.getNextRow（）; row; row = aResultSet.getNextRow（））{ me.results = true; var value = row.getResultByName（name）; } }; this.handleError = function（aError）{ .... //处理错误}; this.handleCompletion = function（aReason）{ if（me.results）{ .... // results } else { .... //无结果} if（aReason！= Components.interfaces.mozIStorageStatementCallback.REASON_FINISHED）{ .... //处理这些}; }; s = new sql（）; $ b $ statement.executeAsync（{ handleResult：s.handleResult， handleError：s.handleError， handleCompletion：s.handleCompletion }）; 是否被认为是解决这个问题的好方法？ edit1：这不符合我所期望的方式（它的工作原理，但不是100％确定为什么）。即，如果handleResult永远不会运行，则this.results变量是未定义的（而不是false）。所以它看起来好像handleResult和handleCompletion正在操作一个不同的变量集合比我所期望的。 任何帮助了解我做错了将不胜感激。 Is this possible easily? It seems the handleResult method is only executed if the result isn't the empty set.A thought I had was to have handleResult and handleCompletion be member functions of an object and have handleResult update a member variable that handleCompletion can check. If the variable is set, not empty, if variable unset, empty and can act accordingly. seems to be overly complicated and hoping there's a better solution? 解决方案 to sketch out a solution (the thought i had above) (edit2: per comment I made below)function sql() { this.results = false; var me = this; this.handleResult = function(aResultSet) { for (var row = aResultSet.getNextRow(); row; row = aResultSet.getNextRow()) { me.results = true; var value = row.getResultByName("name"); } }; this.handleError = function(aError) { .... //deal with error }; this.handleCompletion = function(aReason) { if (me.results) { ....//results } else { ....//no results } if (aReason != Components.interfaces.mozIStorageStatementCallback.REASON_FINISHED) { ....//handle these };};s = new sql(); statement.executeAsync({ handleResult: s.handleResult, handleError: s.handleError, handleCompletion: s.handleCompletion});is this considered a good way to solve this problem?edit1: this doesn't behave in the manner I'd expect (it works, but not 100% sure why). i.e. the this.results variable is undefined (not false), if handleResult never runs. So it appers as if handleResult and handleCompletion are operating on a different set of variables than I'd expect.any help to understand what I'm doing wrong would be appreciated. 这篇关于确定一个SQL select是否异步返回一个空集？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！