MongoDB Query in Python

To query a MongoDB database using Python, you use the find() and find_one() methods from the pymongo library.

1. Install pymongo

Before you start querying MongoDB, ensure that you have the pymongo library installed:

pip install pymongo

2. Connect to MongoDB

Before running queries, establish a connection to your MongoDB instance.

import pymongo# Connect to MongoDBclient = pymongo.MongoClient("mongodb://localhost:27017/")# Select the databasedb = client["mydatabase"]# Select the collectioncollection = db["mycollection"]

3. Querying MongoDB

MongoDB queries in Python use the find() and find_one() methods.

a) Find One Document (find_one())

The find_one() method returns the first document that matches the query.

# Find one document (first record in the collection)document = collection.find_one()print(document)

Find One with a Condition

You can specify a condition to find a specific document.

document = collection.find_one({"name": "Alice"})print(document)

This will return the first document where the name is "Alice".

b) Find Multiple Documents (find())

The find() method returns all documents that match the query.

# Find all documents in the collectiondocuments = collection.find()# Loop through the documents and print themfor doc in documents:    print(doc)

Find Documents with a Condition

You can filter results by passing a query.

query = {"age": {"$gt": 25}}  # Find people with age greater than 25documents = collection.find(query)for doc in documents:    print(doc)

4. Using Projections (Selecting Specific Fields)

By default, find() returns all fields in a document. You can use projections to return only specific fields.

# Retrieve only 'name' and 'city', exclude '_id'documents = collection.find({}, {"_id": 0, "name": 1, "city": 1})for doc in documents:    print(doc)

In this example:

• {"_id": 0} excludes the _id field.

• {"name": 1, "city": 1} includes only the name and city fields.

5. Sorting Results

You can use the sort() method to sort the query results.

# Sort documents by age in ascending orderdocuments = collection.find().sort("age", pymongo.ASCENDING)for doc in documents:    print(doc)

To sort in descending order, use pymongo.DESCENDING.

documents = collection.find().sort("age", pymongo.DESCENDING)for doc in documents:    print(doc)

6. Limit and Skip (Pagination)

To limit the number of results returned, use limit().

# Retrieve only 3 documentsdocuments = collection.find().limit(3)for doc in documents:    print(doc)

To skip a certain number of documents, use skip().

# Skip the first 2 documents and get the next 3documents = collection.find().skip(2).limit(3)for doc in documents:    print(doc)

7. Querying with AND, OR, and NOT

You can use logical operators like $and, $or, and $not to combine conditions.

Using $and

query = {    "$and": [        {"age": {"$gt": 25}},        {"city": "New York"}    ]}documents = collection.find(query)for doc in documents:    print(doc)

Using $or

query = {    "$or": [        {"age": {"$gt": 30}},        {"city": "Los Angeles"}    ]}documents = collection.find(query)for doc in documents:    print(doc)

Using $not

query = {"age": {"$not": {"$gte": 30}}}  # Find people younger than 30documents = collection.find(query)for doc in documents:    print(doc)

8. Closing the Connection

After completing the queries, close the MongoDB connection.

client.close()

Conclusion

These methods help you efficiently query and filter data from MongoDB using Python. ?