MongoDB $in

Summary: in this tutorial, you’ll learn how to use the MongoDB $in operator to select documents where the value of a field equals any value in an array.

Introduction to the MongoDB $in operator

The $in is a comparison query operator that allows you to select documents where the value of a field is equal to any value in an array.

The following shows the syntax of the $in operator:

{ field: { $in: [<value1>, <value2>,...] }}
Code language: CSS (css)

If the field holds a single value, then the $in operator selects documents where the value of the field is equal to any value such as <value1>, <value2>.

In case the field holds an array, the $in operator selects documents where the array contains at least one element that equals any value (<value1>, <value2>).

The value list <value1>, <value2>, etc., can be a list of literal values or regular expressions.

A regular expression is a set of characters that defines a search pattern e.g., /\d+/ any digits such as 1, 123, and 1234.

MongoDB $in operator examples

We’ll use this products collections in the following examples:

db.products.insertMany([
    { "_id" : 1, "name" : "xPhone", "price" : 799, "releaseDate": ISODate("2011-05-14"), "spec" : { "ram" : 4, "screen" : 6.5, "cpu" : 2.66 },"color":["white","black"],"storage":[64,128,256]},
    { "_id" : 2, "name" : "xTablet", "price" : 899, "releaseDate": ISODate("2011-09-01") , "spec" : { "ram" : 16, "screen" : 9.5, "cpu" : 3.66 },"color":["white","black","purple"],"storage":[128,256,512]},
    { "_id" : 3, "name" : "SmartTablet", "price" : 899, "releaseDate": ISODate("2015-01-14"), "spec" : { "ram" : 12, "screen" : 9.7, "cpu" : 3.66 },"color":["blue"],"storage":[16,64,128]},
    { "_id" : 4, "name" : "SmartPad", "price" : 699, "releaseDate": ISODate("2020-05-14"),"spec" : { "ram" : 8, "screen" : 9.7, "cpu" : 1.66 },"color":["white","orange","gold","gray"],"storage":[128,256,1024]},
    { "_id" : 5, "name" : "SmartPhone", "price" : 599,"releaseDate": ISODate("2022-09-14"), "spec" : { "ram" : 4, "screen" : 5.7, "cpu" : 1.66 },"color":["white","orange","gold","gray"],"storage":[128,256]}
 ])
Code language: JavaScript (javascript)

1) Using the $in opeator to match values

The following example uses the $in operator to select documents from the products collection whose the price is either 599 or 799:

db.products.find({
    price: {
        $in: [699, 799]
    }
}, {
    name: 1,
    price: 1
})
Code language: CSS (css)

It returned the following documents:

[
  { _id: 1, name: 'xPhone', price: 799 },
  { _id: 4, name: 'SmartPad', price: 699 }
]
Code language: JavaScript (javascript)

2) Using the $in operator to match values in an array

The products collection has the color array that contains some colors.

The following example uses the $in operator to select documents where the color array has at least one element either "black" or "white":

db.products.find({
    color: {
        $in: ["black", "white"]
    }
}, {
    name: 1,
    color: 1
})
Code language: CSS (css)

The query returned the following documents:

[
  { _id: 1, name: 'xPhone', color: [ 'white', 'black' ] },
  { _id: 2, name: 'xTablet', color: [ 'white', 'black', 'purple' ] },
  {
    _id: 4,
    name: 'SmartPad',
    color: [ 'white', 'orange', 'gold', 'gray' ]
  },
  {
    _id: 5,
    name: 'SmartPhone',
    color: [ 'white', 'orange', 'gold', 'gray' ]
  }
]
Code language: JavaScript (javascript)

3) Using the $in operator with regular expressions

The following query uses the $in operator to find documents where the color array has at least one element that matches either /^g+/ or /^w+/ regular expression:

db.products.find({
    color: {
        $in: [/^g+/, /^w+/]
    }
}, {
    name: 1,
    color: 1
})
Code language: CSS (css)

It returned the following documents:

[
  { _id: 1, name: 'xPhone', color: [ 'white', 'black' ] },
  { _id: 2, name: 'xTablet', color: [ 'white', 'black', 'purple' ] },
  {
    _id: 4,
    name: 'SmartPad',
    color: [ 'white', 'orange', 'gold', 'gray' ]
  },
  {
    _id: 5,
    name: 'SmartPhone',
    color: [ 'white', 'orange', 'gold', 'gray' ]
  }
]
Code language: JavaScript (javascript)

The /^g+/ regular expression matches any string that begins with the letter g and is followed by any number of characters (+). Similarly, the /^w+/ regular expression matches any string that starts with the letter w and is followed by any number of characters (+). This tutorial explains the regular expressions in JavaScript in detail.

Summary

• Use the MongoDB $in operator to select documents where the value of a field is equal to any values in an array.
• The values can be a list of literal values or regular expressions.