节点承诺链是否无法同步执行?
如果我有一系列的promise / function如下例所示,那么函数是否仍有可能无法解决?我有一个函数是mongoose查询和更新,然后另一个函数将数据发送到视图。我的视图正在加载,但没有反映出猫鼬查询结果的正确结果。
let function_one(data) = function(){
return new Promise( function(resolve, reject) {
{do stuff...
resolve('howdy');
}
});
};
let function_two(some_data) = function(){
return new Promise( function(resolve, reject) {
{ do stuff...
resolve('howdy');
}
});
};
let function_three(some_data) = function(){
return new Promise( function(resolve, reject) {
{do stuff...
resolve('howdy');
}
});
};
let function_four(some_data) = function(){
return new Promise( function(resolve, reject) {
{do stuff...
resolve('howdy');
}
});
};
function_one(data).then(function(result){
return function_two(result);
}).then(function(result){
return function_three(result);
}).then(function(result){
return function_four(result);
}).then(function(result){
console.log(result);
}).catch(err => console.log("Caught " + err));
这是我放在一起的代码:就像“res.json({status:200,data:result});”在mongoose发现完成之前正在执行?
let gettheinformation = function(invoicelist3){
return new Promise( function(resolve, reject) {
// console.log(invoicelist3);
Product.aggregate([
{
$match: {
Priced: true
}
}
,
{
$group: {
_id: "$Invoice",
pricedcount: {$sum: 1}
}
}
], function (err, result) {
if (err) {
console.log(err);
} else {
resolve(result);
}
});
});
};
let getinvprodspriced = function(invlist){
return new Promise( function(resolve, reject) {
// console.log(invlist);
for(var oo = 0; oo < invlist.length; oo++){
Invoicestatus.update({Invoice:invlist[oo]._id}, {Noofitemspriced: invlist[oo].pricedcount}, {upsert: true}, function (err) {});
}
resolve(invlist);
});
};
let getinvprodcount = function(invprodcount){
return new Promise( function(resolve, reject) {
Product.aggregate([
{
$group: {
_id: "$Invoice",
pradcount: {$sum: 1}
}
}
], function (err, result) {
if (err) {
console.log(err);
} else {
// console.log(result);
resolve(result);
}
});
});
}
let saveinvprodcount = function(invprodcount){
return new Promise( function(resolve, reject) {
for(var ok = 0; ok < invprodcount.length; ok++){
Invoicestatus.update({Invoice:invprodcount[ok]._id}, {Noofitems: invprodcount[ok].pradcount}, {upsert: true}, function (err) {});
}
resolve(invprodcount);
});
};
let getarrdocs = function(result){
return new Promise( function(resolve, reject) {
Invoicestatus.find({}, function(err, docs){
resolve(docs);
});
});
};
router.get('/fetcharrdata', function(req, res) {
gettheinformation().then(function(result){
return getinvprodspriced(result);
}).then(function(result){
return getinvprodcount(result);
}).then(function(result){
return saveinvprodcount(result);
}).then( function(result){
return getarrdocs(result);
}).then(function(result){
res.json({status: 200, data: result});
}).catch(err => console.log("Caught " + err));
});
回答如下:
问题出在saveinvprodcount方法for循环中,函数将在执行Invoicestatus.update函数之前解析,
let saveinvprodcount = function(invprodcount){
return new Promise( function(resolve, reject) {
for(var ok = 0; ok < invprodcount.length; ok++){
Invoicestatus.update({Invoice:invprodcount[ok]._id}, {Noofitems: invprodcount[ok].pradcount}, {upsert: true}, function (err) {});
}
//this will resolve before completion of Invoicestatus.update
resolve(invprodcount);
});
};
首先使用promisify更新函数然后使用数组来保存promises,你可以使用promise.all一次执行所有的promises。见下文
let saveinvprodcount = function (invprodcount) {
let promises = [];
for (var ok = 0; ok < invprodcount.length; ok++) {
promises.push(updateData(invprodcount[ok]));
}
return Promise.all(promises);
};
let updateData = function (invProd) {
return new Promise(function (resolve, reject) {
Invoicestatus.update({ Invoice: invProd._id },
{ Noofitems: invProd.pradcount }, { upsert: true }, function (err) {
if (err)
reject(err);
else
resolve();
});
});
};