Order and limit results in a query with a callback - node.js

Question

Using Mongoose, I'd like to make a query with MongoDB and order and limit the results I get. I am doing this with Node.js so I am using callbacks.
So far, I have managed to order my results like this:
myModel.find({ $query: {}, $orderby: { created_at : -1 }}, function (err, items) {
callback( null, items )
});
How can I limit the results I get selecting and index and the number of items I want to get?

Answer 1

Using mongodb native:
http://mongodb.github.io/node-mongodb-native/api-generated/collection.html#find
myModel.find(filter)
.limit(pageSize)
.skip(skip)
.sort(sort)
.toArray(callback);
You can also specify the items in your query:
myModel.find(filter, {sort: {created_at: -1}, limit: 10}, function(err, items){
});
There is no $orderby in node mongodb native, so I'm not sure what library or other tool you're using.
...
Now that you've clarified Mongoose (which in general I recommend against):
myModel.find(filter).limit(10).exec(function(err, items){
//process
});

Answer 2

To sort documents, we can apply sort on a cursor object. To enforce order of sort, instead of passing an object, we need to pass an array to the sort method.
var MongoClient = require('mongodb').MongoClient,
commandLineArgs = require('command-line-args'),
assert = require('assert');
var options = commandLineOptions();
MongoClient.connect('mongodb://localhost:27017/crunchbase', function(err, db) {
assert.equal(err, null);
console.log("Successfully connected to MongoDB.");
var query = queryDocument(options);
var projection = {
"_id": 0,
"name": 1,
"founded_year": 1,
"number_of_employees": 1
};
var cursor = db.collection('companies').find(query);
cursor.project(projection);
cursor.limit(options.limit);
cursor.skip(options.skip);
cursor.sort([
["founded_year", 1],
["number_of_employees", -1]
]);
var numMatches = 0;
cursor.forEach(
function(doc) {
numMatches = numMatches + 1;
console.log(doc.name + "\n\tfounded " + doc.founded_year +
"\n\t" + doc.number_of_employees + " employees");
},
function(err) {
assert.equal(err, null);
console.log("Our query was:" + JSON.stringify(query));
console.log("Documents displayed: " + numMatches);
return db.close();
}
);
});
function queryDocument(options) {
console.log(options);
var query = {
"founded_year": {
"$gte": options.firstYear,
"$lte": options.lastYear
}
};
if ("employees" in options) {
query.number_of_employees = {
"$gte": options.employees
};
}
return query;
}
function commandLineOptions() {
var cli = commandLineArgs([{
name: "firstYear",
alias: "f",
type: Number
}, {
name: "lastYear",
alias: "l",
type: Number
}, {
name: "employees",
alias: "e",
type: Number
}, {
name: "skip",
type: Number,
defaultValue: 0
}, {
name: "limit",
type: Number,
defaultValue: 20000
}]);
var options = cli.parse()
if (!(("firstYear" in options) && ("lastYear" in options))) {
console.log(cli.getUsage({
title: "Usage",
description: "The first two options below are required. The rest are optional."
}));
process.exit();
}
return options;
}
One thing to notice is the order in which MongoDB applies skip, limit and sort
sort
skip
limit
There's also a possibility that we can sort data on the MongoDB side as well, provided that we've setup the indexing.
Notice that MongoDB driver will send a query when we call a cursor method passing a callback function to process query results.