NodeJS Express异步问题

Question

I have this function which gets some data from my database but i'm having a trouble calling the function and getting the proper response

  function getEvents()
  {
    var x = [];
    var l = dbCollection['e'].find({}).forEach(function(y) {
    x.push(y);
  });

 return x;
});

and another function which calls this function but it always returns undefined. How can i make the function wait till mongoose has finished filling up the array?

Thanks for the help! My life

Answer 1

dbCollection['e'].find is called non-blocking way so you are returning x before filling. You need to use callbacks or some mongoose promises. You can get all returning values from database like following snippet

function getEvents(callback) {
    dbCollection['e'].find({}, function(error, results) {
        // results is array.
        // if you need to filter results you can do it here
        return callback(error, results); 
    })
}

Whenever you need to call getEvents function you need to pass a callback to it.

getEvents(function(error, results) {
    console.log(results); // you have results here
})

You should read mongoose docs for how queries work.

There is also support for promises in mongoose. You can check this url for more information about promises.

Answer 2

The solution proposed by @orhankutlu should work fine.

I will give another solution using promise. You can choose one between these two solutions depending on your style of programming.

Solution using promise:

function getEvents() {
    return new Promise(function(resolve, reject){
        dbCollection['e'].find({}, function(error, results) {
           if (error) return reject(error);

           var x = [];
           results.forEach(function(y){
              x.push(y);
           });
           // forEach() is a blocking call, 
           // so the promise will be resolved only 
           // after the forEach completes
           return resolve(x); 
        });
    });
};

Calling getEvents():

getEvents().then(function(result){
    console.log(result);   //should print 'x'
}).catch(function(err){
    // Handle error here in case the promise is rejected
});

I will encourage you to try both the approaches, ie, using callbacks and using promises. Hope you find it useful!