MongoDB Data Types Explained

July 16, 2025

When working with databases, understanding data types is essential. In MongoDB, data types define the kind of value that can be stored in a field. This helps MongoDB efficiently store, index, and query the data.

Unlike traditional relational databases, MongoDB uses a flexible, schema-less format based on BSON (Binary JSON). This allows it to support a variety of rich data types beyond simple strings and numbers.

Let’s explore the most commonly used data types in MongoDB, how they are stored, and when to use them.

📦 What is BSON?

Before diving into types, it’s helpful to know that MongoDB stores data in BSON format — a binary version of JSON. BSON supports more data types than JSON (like Date, Decimal128, Binary, etc.), making it more powerful for database operations.

🗂️ Common MongoDB Data Types

Here’s a breakdown of the most commonly used data types in MongoDB:

1. String (`"some text"`)

Represents text data.
Most commonly used data type.
Stored as UTF-8 encoded.

✅ Use When: Storing names, titles, addresses, etc.

2. Number (Int, Long, Double, Decimal128)

int32: 32-bit integer (NumberInt())
int64: 64-bit integer (NumberLong())
double: 64-bit floating point
Decimal128: High precision decimal, ideal for financial data

✅ Use When: You need exact numeric values (e.g., age, price, quantity).

3. Boolean (`true / false`)

Stores a binary true/false value.

✅ Use When: Flags like isActive, isAdmin, etc.

4. Date (`ISODate()`)

Used to store date and time in UTC.
Supports operations like sorting, querying date ranges, etc.

✅ Use When: Tracking timestamps, created/updated times.

5. ObjectId

A unique 12-byte identifier generated automatically for each document.
Used as the default _id field.

✅ Use When: You want a unique key per document.

6. Array

Stores multiple values in a single field.
Can include mixed types (strings, numbers, objects, etc.)

✅ Use When: Tags, lists, multiple addresses, etc.

json
"skills": ["MongoDB", "JavaScript", "Python"]

7. Embedded Document (Object)

A document inside another document.
Allows storing related data in a nested structure.

✅ Use When: Modeling one-to-many or related data (like user and address).

json
"address": {
  "city": "Pune",
  "pin": 411001
}

8. Null

Represents a missing or null value.

✅ Use When: Field is optional or value is unknown.

9. Binary Data

Used to store raw binary data such as images, files, or encrypted content.

✅ Use When: Handling files or non-textual data in MongoDB.

10. Regular Expression (`/pattern/`)

Allows storing and querying text using patterns.

✅ Use When: Searching for patterns in strings (e.g., email validation).

🧪 Example Document with Multiple Types

json
{
  "_id": ObjectId("..."),
  "name": "Sharon",
  "age": 21,
  "isStudent": true,
  "scores": [88, 92, 79],
  "joined": ISODate("2023-10-01T00:00:00Z"),
  "address": {
    "city": "Pune",
    "state": "Maharashtra"
  },
  "interests": null
}

🛡️ Best Practices

Choose the right type for the right data (e.g., use Boolean instead of "true" as a string).
Use Decimal128 for accurate currency calculations.
Index the fields based on type and query usage.
Avoid deeply nested or overly complex documents.

🎯 Final Thoughts

MongoDB's flexible data model lets you work with real-world data structures naturally. Mastering its data types helps you build more efficient, accurate, and scalable applications.

In the next blog, we'll explore "Working with ObjectId and _id in MongoDB", so stay tuned!

Prachi Deokar

University: Shree Balaji University, Pune

School: School of Computer Studies

Course: BCA (Bachelor of Computer Applications)

Interests: NoSQL, MongoDB, and related technologies

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