节点异步-已调用回调-使用2 for循环和if语句 [英] Node Async - Callback was already called - using 2 for loops and an if statement
问题描述
有人可以解释一下为什么我继续看到Error: Callback was already called的原因.
Could someone please explain why I keep seeing the Error: Callback was already called.
我觉得我已经涵盖了所有情况-那么为什么会被已经打电话":
I feel I have covered all cases - so why would be 'already called':
function addVertices(outercallback) {
async.forEachLimit(fullData, 25, function (data, innercallback) {
myJson.matches.forEach(function (oMatches) {
if (data.$.id == oMatches.SourceId) {
oMatches.Ids.forEach(function (oId) {
client.execute("g.addV('test').property('id', \"" + oId + "\")", {}, (err, results) => {
if (err) {
return innercallback(console.error(err));
}
innercallback(null)
});
})
}
})
}, outercallback);
}
事实上，我还尝试用async.ForEach替换第二个forEach，如下所示，但这是正确的方法吗?:
Infact I also tried replacing that second forEach with async.ForEach as in the following, however is this the correct way to go?:
function addVertices(outercallback) {
async.forEachLimit(fullData, 25, function (data, innercallback) {
async.forEach(myJson, function (oMatches, innercallback2) {
if (data.$.id == oMatches.SourceId) {
oMatches.Ids.forEach(function (oId) {
client.execute("g.addV('test').property('id', \"" + oId + "\")", {}, (err, results) => {
if (err) {
return innercallback2(console.error(err));
}
innercallback2(null)
});
})
}
innercallback(null)
})
}, outercallback);
}
推荐答案
这不是if的问题.
但是，由于在async.forEachLimit的每次迭代中，innercallback在myJson.matches.forEach(...)中被调用，由于myJson.matches可能超过一项，因此可能已经多次调用.
But because in each iteration of async.forEachLimit, the innercallback is called in the myJson.matches.forEach(...) which may have been called multiple times since myJson.matches may be more than 1 item.
第二个代码块中存在相同的问题.
在内部async.forEach中，innercallback2在oMatches.Ids.forEach中被调用，也可以被多次调用.
Same problem in your 2nd code block.
In the inner async.forEach, the innercallback2 is called in the oMatches.Ids.forEach which also may be called multiple times.
因此，当您对innercallback的第二次呼叫(或以后的任何呼叫)发生时，将争辩Error: Callback was already called.
Therefore, Error: Callback was already called is argued when your second call (or any later calls) to innercallback occurs.
我已经用Promise#all更新了解决方案，以确保在您的原始帖子中调用innercallback.
请参见 Updated (2018.05.14) 部分和代码块.
I've updated the solution with Promise#all to ensure the call of innercallback in your original post.
See the Updated (2018.05.14) part and the code block.
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