How to create index for MongoDB Collection using Python? (original) (raw)

Last Updated : 4 Jul, 2025

Creating indexes in **MongoDB improves query performance, especially on large datasets. PyMongo, the official MongoDB driver for Python, provides the **create_index() method to define indexes on specific fields. By default, MongoDB indexes the _id field, but adding custom indexes is important for optimizing complex queries.

Syntax

collection.create_index([(field, direction)], **options)

**Parameters:

• **[(field, direction)]: A list of tuples where each tuple contains the field name and the direction (1 for ascending, -1 for descending).
• ****options: (Optional) Additional options such as unique=True makes the index unique and name="custom_index_name" gives a name to the index.

**Returns: This method returns the name of the created index as a string.

Examples

Example 1: Create a single field index

Python `

from pymongo import MongoClient c = MongoClient("mongodb://localhost:27017/") db = c["mydb"] col = db["students"] col.drop()

col.insert_many([ {"name": "Ava", "age": 22}, {"name": "Liam", "age": 24}, {"name": "Emma", "age": 20} ])

idx_name = col.create_index([("name", 1)]) print(idx_name)

`

**Output

name_1

**Explanation: create_index([("name", 1)]) creates an ascending index on the name field to speed up queries and sorting and returns "name_1", the default name based on the field and sort order.

Example 2: Create a compound index (multiple fields)

Python `

from pymongo import MongoClient c = MongoClient("mongodb://localhost:27017/") db = c["mydb"] col = db["students"] col.drop()

col.insert_many([ {"name": "Ava", "city": "New York"}, {"name": "Liam", "city": "Chicago"}, {"name": "Emma", "city": "Boston"} ])

idx_name = col.create_index([("name", 1), ("city", -1)]) print(idx_name)

`

**Output

name_1_city_-1

**Explanation: This creates a compound index on name (ascending) and city (descending). It helps optimize queries that filter or sort on both fields and returns the default index name "name_1_city_-1".

Example 3: Create a unique index

Python `

from pymongo import MongoClient c = MongoClient("mongodb://localhost:27017/") db = c["mydb"] col = db["students"] col.drop()

col.insert_many([ {"email": "ava@example.com"}, {"email": "liam@example.com"}, {"email": "emma@example.com"} ])

idx_name = col.create_index([("email", 1)], unique=True) print(idx_name)

`