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I found 2 ways to execute queries using mongoose find(), but was wondering if they are different:

When should we use:

Model.find({},cb)

And when should we use:

Model.find({}).exec(cb)
TBE
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    Possible duplicate of [Mongoose - What does the exec function do?](http://stackoverflow.com/questions/31549857/mongoose-what-does-the-exec-function-do) – Henrik Andersson Feb 10 '16 at 14:06
  • got it, so basically if i don't chain queries it has no meaning? – TBE Feb 10 '16 at 14:08

2 Answers2

2

Both execute the query and then run the callback.

The main difference is that the first one, returns a Query object while the second returns a Promise which is useful if you need promises.

const query = Model.find({}, cb);

Then you can work with the query variable.

While the promise...

const promise = Model.find({}).exec();

Then you can work with the promise and do things like:

promise.then(cb);
promise.catch((err) => {
  console.error(err);
});

But if you do Model.find({}).exec(cb); the callback is also called without using promises...

I hope it helps

ajimix
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The difference is that the first one executes the query and calls your callback. Whereas in the second one where you omit the callback, the query will not be executed. Instead it will return a Query object which can be used to chain methods, specify search terms, and cursor options, etc...

http://mongoosejs.com/docs/2.7.x/docs/query.html

If you don't need to do any kind of chaining, or anything else with the underlying Cursor then just use the first method.

But the second method can be helpful to do things like:

findCars : function(options, callback) {
    var query = Model.find({});

    if(options.limit) query.limit(options.limit);
    if(options.skip) query.limit(options.skip);

    if(options.populate) query.populate(options.populate);

    return query.exec(callback);
}
officert
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    `.exec()` returns [a promise](http://mongoosejs.com/docs/promises.html#queries-are-not-promises), not a `Query` object (however, as your code is showing correctly, `Model.find()` _does_ return a `Query` object). – robertklep Feb 10 '16 at 14:23