[英]Node.js using multiple promises
我目前尝试使用两种诺言。 一种用于整个会议,另一种用于将用户标识转换为用户名。
上面的输出是我想要的。
我的代码有什么问题? 我需要怎么做才能正确履行诺言?
码:
function getconvensations(userid) {
return new Promise(function(resolve, reject) {
convensations.find({members: userid}).lean().then(function (convensations) {
var promises = convensations.map(function (currentConvensation) {
return new Promise(function (resolve, reject) {
var realnames = [];
var usernames = currentConvensation.members.map(function (CurrentUser) {
Core.userDetails(CurrentUser).then(function (user) {
realnames.push(user.username);
console.log("RESOLVING USERNAMES");
resolve();
});
});
Promise.all(usernames).then(function () {
console.log("GET LATEST MESSAGE");
latestMessage(currentConvensation._id).then(function (message) {
console.log("Messages: ");
console.log(message);
currentConvensation.spesificmessage = message;
currentConvensation.users = realnames;
currentConvensation.otherend = (currentConvensation.members[0] == userid ? realnames[0] : realnames[1]);
console.log("RESOLVE LATEST MESSAGE");
resolve();
});
});
});
});
Promise.all(promises).then(function () {
console.log("FINISHED CONVENSATIONS");
console.log("-------------------------");
console.log(convensations);
console.log("-------------------------");
return resolve(convensations);
}).catch(console.error);
});
});
}
呼叫者:
} else if(action == 'getconvensations') {
Messages_model.getconvensations(req.user._id).then(function (response) {
res.json(response);
});
}
您的比赛条件如下:
new Promise(function (resolve, reject) {
…
currentConvensation.members.map(function (CurrentUser) {
Core.userDetails(CurrentUser).then(function (user) {
resolve();
});
});
…
latestMessage(currentConvensation._id).then(function (message) {
resolve();
});
…
});
任意同时执行许多任务,第一个实现的承诺将调用resolve()
。
解决方案是避免Promise
构造函数反模式,并且永远不要调用new Promise
或手动resolve
! 相反, 连锁承诺回调对方使用then
方法,并return
从每一个新功能的承诺,允许呼叫者等待他们。
function getconvensations(userid) {
return convensations.find({members: userid}).lean().then(function (convensations) {
// ^^^^^^
var promises = convensations.map(function (currentConvensation) {
var usernamepromises = currentConvensation.members.map(function (CurrentUser) {
console.log("GETTING USERNAME");
return Core.userDetails(CurrentUser).then(function (user) {
// ^^^^^^
console.log("FULFILLED USERNAME");
return user.username;
// ^^^^^^
});
});
return Promise.all(usernamepromises).then(function (realnames) {
// ^^^^^^
console.log("FULFILLED ALL USERNAMES");
currentConvensation.users = realnames;
currentConvensation.otherend = (currentConvensation.members[0] == userid ? realnames[0] : realnames[1]);
console.log("GETTING LATEST MESSAGE");
return latestMessage(currentConvensation._id);
// ^^^^^^
}).then(function (message) {
console.log("FULFILLED LATEST MESSAGE");
console.log("Message: ", message);
currentConvensation.spesificmessage = message;
});
});
return Promise.all(promises).then(function () {
// ^^^^^^
console.log("FINISHED ALL CONVENSATIONS");
console.log("-------------------------");
console.log(convensations);
console.log("-------------------------");
return convensations;
// ^^^^^^
});
});
}
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