get-query-modifier

Helper for parsing mongoose mongodb query operators.

What is this?

get-query-modifier is a module designed to help with mongoose query parsing. Let's say you have a GET /api/comments endpoint, in your API like the following:

app.get('/api/comments', function(req, res) {
  Comment
    .find()
    .lean()
    .exec(function(err, comments) {
      if(err) res.json(err.status || 500, { error: err.message });
      else res.json({ comments: comments });
    });
});

Suddenly, you decided to add pagination to this route. You could easily implement calls with mongoose's Query.prototype.limit and Query.prototype.skip, as follows:

app.get('/api/comments', function(req, res) {
  Comment
    .find()
    .skip(req.query.page * req.query.items_per_page)
    .limit(req.query.items_per_page)
    .exec(/**/);
});

Or something like that.

You'd be, however, recreating your own query syntax.

You can get a lot more power by using mongodb's default query syntax, extending it where mongoose/mongodb expose a slightly different API, such as .limit, .skip etc.

get-query-modifier solves this solution by extracting the operators $sort, $limit, $skip, $page and $select (plus any operator you want to support by setting options.allow), and translating them into a set of method calls to the query object (calls to Query.prototype.sort, Query.prototype.select etc.). This allows maximum flexibility for using both the req.query object for further querying in the mongoose API and supporting a known standard set of operators, which come out-of-the-box in mongodb.

It does it by taking the query object as its first argument and returning a modifier function, which handles calling each of these deferred Query method calls once your Query instance is available.

app.get('/api/comments', function(req, res) {
  var modifier = getQueryModifier(req.query);
  // `req.query` had its `$limit`, `$sort`, `$page`, `$skip` and `$select`
  // fields striped from it and translated into a set of method calls in
  // `modifier`

  var query = Comment
    .find(req.query) // we can create an arbitrary Query, re-using `req.query`
    .lean();

  modifier(query) // modifier applies the extracted operators to the Query
    .exec(/**/);
});

getQueryModifier(query, [options])

Manipulates an object representation of a querystring, extracting its mongoose query operators and returning a function to attach them to a mongoose.Query object.

Note this function isn't pure and does delete the operators from the query parameter after reading them.

Params:

• Object query The querystring representation to manipulate
• Object [options] An options object
• Object [options.defaults] An object with defaults for the valid operators
• Object [options.ignore] An object with the properties corresponding to the ignored operators set to true
• Boolean [options.deleteIgnored=false] Whether to delete the ignored operators from the query object
• Array. [options.allow] An array of operators to parse in addition to the plugin's default VALID_OPERATORS.

Return:

• Function queryModifier The mongoose.Query modifier function, which attaches the operators to the search

Example:

var app = require('./app'); // some express app
var mongoose = require('mongoose');
var User = mongoose.model('User'); // some mongoose model

app.get('/api/users', function(req, res) {
  var modifier = getQueryModifier(req.query);
  var query = modifier(User.find(req.query).lean());

  query.exec(function(err, results) {
    // use the results...
  });
});

See the tests for more elaborate examples.

getQueryModifier.middleware([options])

A connect middleware for parsing and using mongodb query operators with mongoose given an object representation of a query.

Params:

• Object [options] An options object which will simply be passed onto getQueryModifier(req.query, options)

Return:

• Function mdw The middleware function

Example:

var app = require('./app'); // some express app
app.use(getQueryModifier.middleware());

License

This code is licensed under the MIT License. See LICENSE for more information.