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": "[email protected]"},
{"name": "Bob", "email": "[email protected]"},
{"name": "Charlie", "email": "[email protected]"}
]
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 OutputExplanation: 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
OutputExplanation: 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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