Indexing in MongoDB using Python

Last Updated : 15 Jul, 2025

In PyMongo, indexing is used to improve the performance of queries by allowing MongoDB to quickly locate and access the requested data without scanning every document in a collection. create_index() defines indexes to optimize queries and enforce constraints. MongoDB auto-indexes _id, but custom indexes can be added on fields using various directions and options.


Syntax

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

Parameters:

  • field: Field to index (e.g., "name")
  • direction: pymongo.ASCENDING or pymongo.DESCENDING
  • options: Additional index options like unique=True, name="customIndex" etc.

Here is our sample data.

Python 
from pymongo import MongoClient, ASCENDING
c = MongoClient("mongodb://localhost:27017/")
db = c["indexDB"]
col = db["users"]

data = [
    {"name": "Alice", "email": "alice@example.com"},
    {"name": "Bob", "email": "bob@example.com"},
    {"name": "Charlie", "email": "charlie@example.com"}
]

col.delete_many({})
col.insert_many(data)
print("Sample data inserted.")

Output

Sample data inserted
Output
Sample data

Explanation:

  • Connects to the local MongoDB server and selects the indexDB database and users collection.
  • Clears existing documents in the collection using delete_many({}).
  • Inserts three sample user records into the collection using insert_many().

Examples

Example 1: Create index on a field

Python 
from pymongo import MongoClient, ASCENDING
c = MongoClient("mongodb://localhost:27017/")
db = c["indexDB"]
col = db["users"]

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

Output

Output

Explanation: Creates an ascending index on the name field to speed up queries using name.

Example 2: List all index

Python 
from pymongo import MongoClient, ASCENDING
c = MongoClient("mongodb://localhost:27017/")
db = c["indexDB"]
col = db["users"]

for idx in col.list_indexes():
    print(idx)

Output

Output
Snapshot of the Output

Explanation: Displays all indexes on the users collection. The default _id_ index and the created name_1 index will be shown.

Example 3: Drop an index

Python 
from pymongo import MongoClient, ASCENDING
c = MongoClient("mongodb://localhost:27017/")
db = c["indexDB"]
col = db["users"]

col.drop_index("name_1")

Output

Index dropped

Explanation: Drops the index named "name_1". You must pass the exact index name created earlier.

Example 4: Create index on a new field (default ascending)

Python 
from pymongo import MongoClient, ASCENDING
c = MongoClient("mongodb://localhost:27017/")
db = c["indexDB"]
col = db["users"]

res = col.create_index("index_created")
print(res)

Output

index_created_1

Explanation: Creates an ascending index (default) on a new field index_created.

Example 5: Create compound index

Python 
from pymongo import MongoClient, ASCENDING
c = MongoClient("mongodb://localhost:27017/")
db = c["indexDB"]
col = db["users"]

res = col.create_index([
    ("ascending_index", 1),
    ("second_descending_index", DESCENDING)
])
print(res)

Output

Output
Output

Explanation: ascending_index is indexed in ascending order, second_descending_index in descending order. This index improves performance for queries and sorts using both fields together.

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