MongoDB Data Types

Summary: in this tutorial, you will learn about the most commonly used MongoDB data types.


The null type is used to represent a null and a field that does not exist. For example:

{ "isbn": null }
Code language: JSON / JSON with Comments (json)


The boolean type has two values true and false. For example:

{ "best_seller": true }
Code language: JSON / JSON with Comments (json)


By default, the mongo shell uses the 64-bit floating-point numbers. For example:

{ "price": 9.95, "pages": 851 }
Code language: JSON / JSON with Comments (json)

The NumberInt and NumberLong classes represent 4-byte and 8-byte integers respectively. For example:

{ "year": NumberInt("2020"), "words": NumberLong("95403") }
Code language: JSON / JSON with Comments (json)


The string type represents any string of UTF-8 characters. For example:

{ "title": "MongDB Data Types" }
Code language: JSON / JSON with Comments (json)


The date type stores dates as 64-bit integers that represents milliseconds since the Unix epoch (January 1, 1970). It does not store the time zone. For example:

{ "updated_at": new Date() }
Code language: JSON / JSON with Comments (json)

In JavaScript, the Date class is used to represent the date type in MongoDB.

Note that you should always call the new Date(), not just Date() when you create a new Date object because the Date() returns a string representation of the date, not the Date object.

The mongo shell displays dates using local time zone settings. However, MongoDB does not store time zone with date. To store the time zone, you can use another key e.g., timezone.

Regular Expression

It’s possible to store JavaScript’s regular expressions. For example:

{ "pattern": /\d+/ }
Code language: JSON / JSON with Comments (json)


The array type allows you to store a list of values of any types. The values do not have to be in the same type, for example:

{ "title": "MongoDB Array", "reviews": ["John", 3.5, "Jane", 5] }
Code language: JSON / JSON with Comments (json)

The good thing about arrays in the document is that MongoDB understands their structures and allows you to carry operations on their elements.

For example, you can query all documents where 5 is an element of the reviews array. Also, you can create an index on the reviews array to improve the query performance.

Embeded Document

A value of a document can be another document which is often referred to as an embeded document.

The following example shows a book document that contains the author document as an embeded document:

{ "title": "MongoDB Tutorial", "pages": 945, "author": { "first_name": "John", "last_name": "Doe" } }
Code language: JSON / JSON with Comments (json)

In this example, the author document has its own key/value pairs including first_name and last_name.

Object ID

In MongoDB, every document has an "_id" key. The value of the "_id" key can any type. However, it defaults to an ObjectId.

The value of the "_id" key must be unique within a collection so that MongoDB can identify every document in the collection.

The ObjectId class is the default type for "_id". It is used to generate a unique values globally across servers. Since MongoDB is designed to be distributed, it is important to ensure the identifiers to be unique in the shared environment.

The ObjectId uses 12 bytes for storage, where each byte represents 2 hexadecimal digits. In total, an ObjectId is 24 hexadecimal digits.

The 12-byte ObjectId value consists of:

  • A 4-byte timestamp value that represents the ObjectId‘s generated time measured in seconds since the Unix epoch.
  • A 5-byte random value.
  • A 3-byte increment counter, initialized to a random value.

These first 9 bytes of an ObjectId gurantees its uniqueness across servers and processes for a single second. The last 3 bytes gurantees the uniqueness within a second in a single process.

As a result, these 12-bytes allow for up to 2563 (16,777,216) unique ObjectIds values to be generated per process in a single second.

When you insert a document without specifying a value for the "_id" key, MongoDB automatically generates an unique id for the document. For example:

db.books.insertOne({ "title": "MongoDB Basics" });
Code language: JavaScript (javascript)


{ "acknowledged" : true, "insertedId" : ObjectId("5f2fcae09b58c38603442a4f") }
Code language: JSON / JSON with Comments (json)

MongoDB generated the id with the value ObjectId("5f2fcae09b58c38603442a4f"). You can view the inserted document like this:

Code language: CSS (css)


{ "_id" : ObjectId("5f2fcae09b58c38603442a4f"), "title" : "MongoDB Basics" }
Code language: JSON / JSON with Comments (json)

In this tutorial, you have learned the most commonly used MongoDB data types including null, number, string, array, regular expression, date, and ObjectId.

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