问题描述
我对异步的Node.js和Mongoose感到有些困惑.简而言之，我要发布一个用户名数组，并检查用户名是否在数据库中，然后将其放在valid数组中，否则，将其放在invalid数组中.
I am some cofused by asychronous nodejs and mongoose. Simplily, I want to post an array of usernames and check, if a username is in database, then I put it in the valid array, otherwise, put it in the invalid array.
这是我当前的代码:
var User = require('../../db/models/user');
api.post('/userlist', function(req, res) {
var invalid = []; // usernames which can not be found in database
var valid = []; // usernames which can be found in database
(req.body.userlist).forEach(function(username) {
User
.findOne({username: username})
.exec(function(err, user) {
if (err) {
res.send(err);
return;
} else if (!user) {
invalid.push(username);
} else {
valid.push(req.params.item);
}
});
});
res.send({
Invalid: invalid,
Valid: valid
});
});
当我执行上面的代码时，它直接输出初始空数组.
When I executed the above code, it outputs the intial empty array directly.
Invalid: [],
Valid: []
我知道这是因为nodejs首先执行此res.send然后执行功能.exec(function(err, user)，但是我不知道如何获得正确的invalid和valid数组，请告知.
I know it is because nodejs first execute this res.send then execute function .exec(function(err, user), but i do not know how to get the right invalid and valid array, pls advise.
推荐答案
您最好的选择是使用诺言:
Your best bet is to use a promise:
api.post('/userlist', (req, res) => {
// Takes a username and returns a promise for information on that username.
function findByUsername(username) {
return new Promise((resolve, reject) =>
User.findOne({username}).exec((err, user) =>
err ? reject(err) : resolve(user)
)
);
}
// Iterate the array and transform each user to a promise for data on that user.
Promise.all(req.body.userlist.map(findByUsername))
// Then, when all of the promises in that new array resolve
.then(allUserDataInOrder => {
// Find all the valid ones (if (user))
let Valid = allUserDataInOrder.filter(Boolean); // Only those who are truthy
// And all the invalid ones (if (!user))
let Invalid = allUserDataInOrder.filter(userData => !userData); // Sadly, no convenient function here :(
// And send both away
res.send({Valid, Invalid}); // Short syntax FTW!
})
.catch(res.send); // Called with error object if any.
});
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