猫鼬模型将多个功能应用于模型对象

Question

I'm usting Nodejs Expressjs MongoDB and Mongoose to create rest API for a small service-app I work on.

I did all routes applying single straightforward functions like .find() .findOneAndUpdate() and etc. Like this one:

    router.get('/testTable', function(req, res, next) {
    TestModel.find(function (err, testTableEntries) {
        if (err) return next(err);
        res.send(testTableEntries);
    });
});

Pretty simple. But, what if I want to incorporate more functions then just single mongo function .find()

What if I want to:

 .find().pretty()

Or if want to aggregate, make some counts:

.find().count()
.find({"fieldName": "How many have this value?"}).count()
.find({"fieldName": "How many have this value?"}).count().pretty()

I tried something like:

    router.get('/testTable', function(req, res, next) {
    TestModel.find(function (err, testTableEntries) {
        if (err) return next(err);
        res.send(testTableEntries);
    }).count();
});

Or maybe you can advice callbackless solution with promise (like Bluebird), my first thought is:

router.get('/testTable', function(req, res, next) {
    TestModel.find(function (err, next) {
        if (err) return next(err);
    }).then(function (req, res, next) {
        res.send(testTableEntries);
    }).catch(function (err, next) {
        if (err) return next(err);
    });
});    

Maybe there's some Mongoose built-in functions that can solve it, I'll be grateful, but also would be useful to know how to call functions in chain one after another on Mongoose Models.

I'm grateful in advance for any advises and thoughts!

Answer 1

Well you can always just call .count() directly:

Test.count({"fieldName": "How many have this value?"},function(err,count) { 
   // count is the counted results
});

And of course the object returned from `.find() in mongoose is an array, so:

Test.find({"fieldName": "How many have this value?"},function(err,results) {
    var count = results.length;
})

Or for "chaining" you can do this with "query" .count()

Test.find({"fieldName": "How many have this value?"})
   .count().exec(function(err,results) {
})

And if you want the "counts" of all possible "fieldName" values then use .aggregate() :

Test.aggregate([
    { "$group": {
        "_id": "fieldName",
        "count": { "$sum": 1 }
    }},
],function(err,results) {
   // each result has a count
});

You generally need to start thinking in terms of "working inside" the callback in async programming and not "returning" results from your method call to an "outside" variable.