确定一个SQL select是否异步返回一个空集？ [英] Determing if a SQL select returns an empty set asynchronously?

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

< （编辑2：每个评论我下面）

  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.

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