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With this package you can parse and convert query parameters into MongoDB query criteria and options.


npm install qs-to-mongo


import qs2m from 'qs-to-mongo' // or const qs2m = require('qs-to-mongo')
const result = qs2m('name=john&age>21&fields=name,age&sort=name,-age&offset=10&limit=10')

The result will be

  criteria: {
    name: 'john',
    age: { $gt: 21 }
  options: {
    fields: { name: true, age: true },
    sort: { name: 1, age: -1 },
    offset: 10,
    limit: 10

Resulting object props (criteria and options) are usable as parameters to any MongoDB package. For example:

import qs2m from 'qs-to-mongo'
import { MongoClient } from 'mongodb'

;(async function() {
    const { db } = await MongoClient.connect(connectionString)
    const result = qs2m('name=john&age>21&fields=name,age&sort=name,-age&offset=10&limit=10')
    const documents = await db('dbName')
      .find(result.criteria, result.options)


Main function

qs2m(query: string, options: {
  ignoredFields?: string | string[]
  parser?: {
    parse(query: string, options?: any): any
    stringify(obj: object, options?: any): string
  parserOptions?: object
  dateFields?: string | string[]
  objectIdFields?: string | string[]
  fullTextFields?: string | string[]
  parameters?: Partial<typeof defaultParameters>
  maxLimit?: number


  • ignoredFields: array of query parameters that are ignored, in addtion to defalut ones: "fields", "omit", "sort", "offset", "limit", "q";
  • parser: custom query parser, must implement parse(query: string, options?: any): any and stringify(obj: object, options?: any): string. The default parser is qs;
  • parserOptions: options to pass to the query parser;
  • dateFields: fields that will be converted to Date. If no fields are passed, any valid date string will be converted to ISOString;
  • objectIdFields: fields that will be converted to ObjectId;
  • fullTextFields: fields that will be used as criteria when passing q query parameter;
  • parameters: override default parameters used as query options ("fields", "omit", "sort", "offset", "limit", "q"). For example: {fields:'$fields', omit:'$omit', sort:'$sort', offset:'$offset', limit:'$limit'};
  • maxLimit: maximum limit that could be passed to limit option.

Returned object

    criteria: {
        [key: string]: any
    options: {
      projection: {
        [key: string]: 0 | 1
      sort: {
        [key: string]: 1 | -1
      skip: number
      limit: number
    links: (url: string, totalCount: number) => {
        prev: string
        first: string
        next: string
        last: string
    } | null

links method examples

import qs2m from 'qs-to-mongo' //or const qs2m = require('qs-to-mongo')
const query = qs2m('name=john&age>21&offset=20&limit=10')
query.links('http://localhost/api/v1/users', 100)

This will generate an object that could be used by express res.links method.

{ prev: 'http://localhost/api/v1/users?name=john&age%3E21=&offset=10&limit=10',
  first: 'http://localhost/api/v1/users?name=john&age%3E21=&offset=0&limit=10',
  next: 'http://localhost/api/v1/users?name=john&age%3E21=&offset=30&limit=10',
  last: 'http://localhost/api/v1/users?name=john&age%3E21=&offset=90&limit=10' }


Any query parameters other then the special parameters fields, omit, sort, offset, limit and q are interpreted as query criteria. For example name=john&age>21 results in a criteria value of:

  'name': 'john',
  'age': { $gt: 21 }
  • Supports standard comparison operations (=, !=, >, <, >=, <=).
  • Numeric values, where Number(value) != NaN, are compared as numbers (ie., field=10 yields {field:10}).
  • Values of true and false are compared as booleans (ie. {field: true})
  • ObjectId hex strings can be compared as ObjectId instances, if objectIdFields is passed.
  • Values that are dates are compared as dates (except for YYYY which matches the number rule) if dateFields is passed. If not, they will be converted to Date ISOString.
  • null values are compared as null. For example bar=null yields {bar: null}
  • special q query parameter could be used to perform fulltext search on fields that are passed in fullTextFields argument.
  • Multiple equals comparisons are merged into a $in operator. For example, id=a&id=b yields {id:{$in:['a','b']}}.
  • Multiple not-equals comparisons are merged into a $nin operator. For example, id!=a&id!=b yields {id:{$nin:['a','b']}}.
  • Comma separated values in equals or not-equals yeild an $in or $nin operator. For example, id=a,b yields {id:{$in:['a','b']}}.
  • Regex patterns. For example, name=/^john/i yields {id: /^john/i}.
  • Parameters without a value check that the field is present. For example, foo&bar=10 yields {foo: {$exists: true}, bar: 10}.
  • Parameters prefixed with a not (!) and without a value check that the field is not present. For example, !foo&bar=10 yields {foo: {$exists: false}, bar: 10}.
  • Supports some of the named comparision operators ($type, $size and $all). For example, foo:type=string, yeilds { foo: {$type: 'string} }.
  • Support for forced string comparison; value in single or double quotes (field='10' or field="10") would force a string compare. Allows for string with embedded comma (field="a,b") and quotes (field="that's all folks").

Embedded documents

Comparisons on embedded documents should use mongo's dot notation instead of qs (Use instead of foo[bar]=value) 'extended' syntax.

Although exact matches are handled for either method, comparisons (such as foo[bar]!=value) are not supported because the qs parser expects an equals sign after the nested object reference; if it's not an equals the remainder is discarded.

Overriding parameters

You can adjust the default parameters (fields, omit, sort, offset, limit and q) by providing an alternate set as an option. For example:

const parameters = {
  q: '$q',

const query = q2m(res.query, { parameters: parameters });

This will then interpret the default parameters as query parameters instead of options. For example a query of age>21&omit=false&$omit=a results in a criteria value of:

query.criteria = {
  'age': { $gt: 21 },
  'omit': false

and an option value of:

query.option = {
  fields: { a: false }

Frameworks integration

This module takes also parsed query as input, so it could be used by Fastify or express routes without any further addition.

const querystring = require('querystring')
const qs2m = require('qs-to-mongo')
const query = 'name=john&age>21&fields=name,age&sort=name,-age&offset=10&limit=10'
const q = q2m(querystring.parse(query))

This makes it easy to use it in fastify route:

fastify.get('/api/v1/mycollection', (req, reply) =>{
  const q = q2m(req.query);

or in express one:

router.get('/api/v1/mycollection', function(req, res, next) {
  const q = q2m(res.query);

The format and names for query parameters was inspired by this article about best practices for RESTful APIs.


This package started as hard fork of This is a TypeScript port, with some fixes and many improvements. Because of the changes to the public API, this is not a drop-in replacement.

Notable differences with query-to-mongo

  • uses qs instead of querystring for default query parsing
  • adds support for null and ObjectId hex string values
  • adds passing options to parser with parserOptions parameter
  • adds support for fulltext search on predefined fields (using fullTextFields parameter)
  • opt-ins date-string conversion to Date with dateFields parameter
  • opt-ins hexstring ObjectId parsing with objectIdFields parameter
  • renames keywords parameter to parameters
  • renames ignore to ignoredFields
  • renames fields to projection in returnd mongo options
  • removes unused and old code
  • written in TypeScript, typed out of the box




Parse and convert query parameters into MongoDB query criteria and options.







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