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I was reading How to use MongoDB with promises in Node.js? when I saw that in the first answer they say that if I pass no callback, mongo driver will return me a promise. It worked for 'connect' but it didn't work when I tried:

db.collection('myCollection').find().then((docs)=>{console.log(docs)})

I got:

MongoDB error: TypeError: db.collection(...).find(...).then is not a function

I tried to read the documentation for find() at http://mongodb.github.io/node-mongodb-native/2.2/api/Collection.html#find and I can see some examples there that does things like this:

collection.find({}).explain().then(function(docs) {
      test.ok(docs != null);

      db.close();
    });

this is a Promise for find but it has this explain() thing. What is it? Also, why there is no mention of promises in this API? There's also another line that does:

collection.insertMany([{a:1}, {a:2}, {a:3}], {w:1}).then(function(result) {

which is also a promise.

So, how to use promises with find()?

Also, why this documentation won't tell the return values of anything? Neither the arguments I can use...

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Gatonito
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1 Answers1

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What you are looking for is toArray(), which works like you want (callback inside, or promise returned if not callback)

db.collection('...').find().toArray()
.then(function(docs) {
  // =)
});

This is because db.collection('..').find() returns a cursor, not a promise.

This behavior is intended because "find as a whole" is not the only pattern that can be used (ie. streams are allowed).

Cyril CHAPON
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