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我正在嘗試使用.forEach完成firebase對象上的幾個循環，並且我還使用了promise。這並不是我計劃的方式。我的基本問題是，承諾鏈本身完成後，我的承諾中的循環完好無損。這裏是我的功能：完成node.js內部的循環承諾
var queue = new Queue(productUpdateQueue, function(data, progress, resolve, reject) {
var incomingUpdateData = data;
var receiptID = incomingUpdateData.receiptID;
var userID = incomingUpdateData.userID;
var oldProductID = incomingUpdateData.oldProductID;
var newProductID = incomingUpdateData.newProductID;
var newReceipt = incomingUpdateData.newReceipt;
var postID = "";
var updateObject = {};
updateObject['usersPrivate/'+userID+'/receipts/'+receiptID+'/items/'+oldProductID] = null;
updateObject['usersPrivate/'+userID+'/receipts/'+receiptID+'/items/'+newProductID] = newReceipt;
clicks.child('VigLink').orderByChild('item').equalTo(oldProductID).once('value', function(cuidSnapshot) {
return cuidSnapshot.forEach(function(cuidSnapshot) {
var cuid = cuidSnapshot.key;
updateObject['clicks/VigLink/'+cuid+'/item'] = newProductID;
console.log('one');
progress(20);
});
}).then(function() {
return userReceiptMetrics.child(userID).child('receipts').child(receiptID).child('items').child(oldProductID).once('value', function(oldSnapshot) {
var data = oldSnapshot.val()
updateObject['userReceiptMetrics/'+userID+'/receipts/'+receiptID+'/items/'+oldProductID] = null
updateObject['userReceiptMetrics/'+userID+'/receipts/'+receiptID+'/items/'+newProductID] = data
if (data != null) {
updateObject['userReceiptMetrics/'+userID+'/receipts/'+receiptID+'/itemIDs/'+newProductID] = now
updateObject['userReceiptMetrics/'+userID+'/receipts/'+receiptID+'/itemIDs/'+oldProductID] = null
};
console.log('two');
progress(40);
});
}).then(function() {
return userReceiptMetrics.child(userID).child('shops').child(oldProductID).once('value', function(oldSnapshot) {
var data = oldSnapshot.val()
updateObject['userReceiptMetrics/'+userID+'/shops/'+oldProductID] = null;
updateObject['userReceiptMetrics/'+userID+'/shops/'+newProductID] = data;
if (data != null) {
updateObject['userReceiptMetrics/'+userID+'/shopIDs/'+newProductID] = now;
updateObject['userReceiptMetrics/'+userID+'/shopIDs/'+oldProductID] = null;
};
console.log('three');
progress(60);
});
}).then(function() {
posts.once('value', function(postSnapshot) {
// use Promise.all and Array#map to wait for all these queries to finish
var allPosts = postSnapshot.val()
var postKeys = Object.keys(allPosts)
return Promise.all(postKeys.map(function(postKey) {
var postID = postKey;
return posts.child(postID).child('items').child(oldProductID).once('value', function(itemSnapshot) {
return itemSnapshot.forEach(function(itemSnapshot) {
var itemData = itemSnapshot.val()
console.log('post snapshot'+ itemData);
updateObject['posts/'+postID+'/items/'+oldProductID] = null
updateObject['posts/'+postID+'/items/'+newProductID] = itemData
});
});
}));
});
}).then(function() {
// Move to next item
return console.log('hey look here'+updateObject['posts/'+postID+'/items/'+newProductID]);
return firebaseRoot.update(updateObject, function(error) {
if (error) {
console.log("Error updating data:", error);
reject()
} else {
progress(100);
// resolve();
console.log('four');
}
});
}).then(function() {
// Move to next item
return console.log('second one'+updateObject['posts/'+postID+'/items/'+newProductID]);
return firebaseRoot.update(updateObject, function(error) {
if (error) {
console.log("Error updating data:", error);
reject()
} else {
progress(100);
// resolve();
console.log('four');
}
});
});
// Finish the task asynchronously
setTimeout(function() {
reject();
}, 10000);
});
，這裏是輸出：
one
two
three
hey look hereundefined
second oneundefined
post snapshot[object Object]
post snapshot[object Object]
post snapshot[object Object]
post snapshot[object Object]
post snapshot[object Object]
post snapshot[object Object]
post snapshot[object Object]
post snapshot[object Object]
我想我可能會錯誤地使用承諾，但我不知道。
我從來沒有火力點前使用，但它看起來像你使用'.once'不正確;至少根據[這些文檔]（https://firebase.google.com/docs/database/web/read-and-write） - 我想你的意思是使用'.on（'value，fn）。然後...）'而不是'.once'。除此之外，'forEach'返回'undefined'，所以你可能想要返回/解決比這更有意義的事情。也許看看'Array.prototype.map'。對不起，我無法提供更多幫助。 – naomik