Indexing in MongoDB using Python (original) (raw)

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

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

**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

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)

`