
In real-world applications, data often changes. MongoDB, being a flexible NoSQL database, allows for seamless updates to documents using Python and the PyMongo driver.
This tutorial will guide you step by step through updating documents in MongoDB using Python, including how to update single or multiple documents, use update operators, and avoid common pitfalls.
Table of Contents
-
Introduction
-
Prerequisites
-
Installing PyMongo
-
Connecting to MongoDB
-
Inserting Sample Data
-
update_one()
– Update a Single Document -
update_many()
– Update Multiple Documents -
Using Update Operators (
$set
,$inc
,$unset
) -
Full Working Example
-
Tips and Common Pitfalls
1. Introduction
Updating documents in MongoDB involves modifying the fields of one or more documents using update methods provided by PyMongo:
-
update_one()
– Updates the first document that matches the filter. -
update_many()
– Updates all documents that match the filter.
⚙️ 2. Prerequisites
-
Python 3.x installed
-
MongoDB running locally or in the cloud (MongoDB Atlas)
-
Basic understanding of Python and MongoDB
3. Installing PyMongo
Install PyMongo via pip:
pip install pymongo
4. Connecting to MongoDB
Connect to MongoDB (local or cloud):
import pymongo
client = pymongo.MongoClient("mongodb://localhost:27017/")
db = client["mydatabase"]
collection = db["users"]
5. Inserting Sample Data
Before updating, let’s insert some documents into a users
collection:
collection.insert_many([
{"name": "Alice", "age": 25, "city": "New York"},
{"name": "Bob", "age": 30, "city": "San Francisco"},
{"name": "Charlie", "age": 35, "city": "New York"},
])
6. update_one()
– Update a Single Document
Use update_one()
to update the first matching document:
collection.update_one(
{"name": "Alice"}, # Filter
{"$set": {"city": "Los Angeles"}} # Update
)
This changes Alice's city from New York to Los Angeles.
7. update_many()
– Update Multiple Documents
Use update_many()
to update all matching documents:
collection.update_many(
{"city": "New York"},
{"$set": {"city": "Chicago"}}
)
All users from New York are now updated to Chicago.
8. Using Update Operators
MongoDB offers powerful update operators:
$set
– Set a field’s value
{"$set": {"field": value}}
$inc
– Increment a numeric value
collection.update_one(
{"name": "Bob"},
{"$inc": {"age": 1}} # Increments Bob's age by 1
)
$unset
– Remove a field
collection.update_one(
{"name": "Charlie"},
{"$unset": {"city": ""}} # Removes the 'city' field
)
9. Full Working Example
import pymongo
# Connect to MongoDB
client = pymongo.MongoClient("mongodb://localhost:27017/")
db = client["mydatabase"]
collection = db["users"]
# Insert sample data
collection.insert_many([
{"name": "Alice", "age": 25, "city": "New York"},
{"name": "Bob", "age": 30, "city": "San Francisco"},
{"name": "Charlie", "age": 35, "city": "New York"}
])
# Update Alice's city
collection.update_one(
{"name": "Alice"},
{"$set": {"city": "Los Angeles"}}
)
# Increment Bob's age
collection.update_one(
{"name": "Bob"},
{"$inc": {"age": 1}}
)
# Update all New York users to Chicago
collection.update_many(
{"city": "New York"},
{"$set": {"city": "Chicago"}}
)
# Remove 'city' from Charlie
collection.update_one(
{"name": "Charlie"},
{"$unset": {"city": ""}}
)
10. Tips and Common Pitfalls
Tip / Pitfall | Explanation |
---|---|
✅ Always use $set with update methods |
Otherwise, you risk replacing the entire document |
✅ Check the result object | Use result.modified_count to verify how many docs were updated |
❌ Avoid omitting the update operator | This would overwrite the entire document accidentally |
✅ Use upsert=True when needed |
Allows insert if no document matches |
✅ Test filters before applying updates | Prevents accidental updates to multiple documents |
✅ Conclusion
Updating documents in MongoDB with PyMongo is both powerful and flexible. Whether you need to update a single record, multiple records, or remove fields altogether, PyMongo provides the tools to do it cleanly and safely.
Mastering MongoDB updates ensures that your applications can handle real-world data changes with precision and confidence.
Tips and Tricks
What is pass in Python?
Python | Pass Statement
The pass statement is used as a placeholder for future code. It represents a null operation in Python. It is generally used for the purpose of filling up empty blocks of code which may execute during runtime but has yet to be written.
def myfunction():
pass
How can you generate random numbers?
Python | Generate random numbers
Python provides a module called random using which we can generate random numbers. e.g: print(random.random())
We have to import a random module and call the random() method as shown below:
import random
print(random.random())
The random() method generates float values lying between 0 and 1 randomly.
To generate customized random numbers between specified ranges, we can use the randrange() method
Syntax: randrange(beginning, end, step)
import random
print(random.randrange(5,100,2))
What is lambda in Python?
Python | Lambda function
A lambda function is a small anonymous function. This function can have any number of parameters but, can have just one statement.
Syntex:
lambda arguments : expression
a = lambda x,y : x+y
print(a(5, 6))
It also provides a nice way to write closures. With that power, you can do things like this.
def adder(x):
return lambda y: x + y
add5 = adder(5)
add5(1) #6
As you can see from the snippet of Python, the function adder takes in an argument x and returns an anonymous function, or lambda, that takes another argument y. That anonymous function allows you to create functions from functions. This is a simple example, but it should convey the power lambdas and closures have.
What is swapcase() function in the Python?
Python | swapcase() Function
It is a string's function that converts all uppercase characters into lowercase and vice versa. It automatically ignores all the non-alphabetic characters.
string = "IT IS IN LOWERCASE."
print(string.swapcase())
How to remove whitespaces from a string in Python?
Python | strip() Function | Remove whitespaces from a string
To remove the whitespaces and trailing spaces from the string, Python provides a strip([str]) built-in function. This function returns a copy of the string after removing whitespaces if present. Otherwise returns the original string.
string = " Python "
print(string.strip())
What is the usage of enumerate() function in Python?
Python | enumerate() Function
The enumerate() function is used to iterate through the sequence and retrieve the index position and its corresponding value at the same time.
lst = ["A","B","C"]
print (list(enumerate(lst)))
#[(0, 'A'), (1, 'B'), (2, 'C')]
Can you explain the filter(), map(), and reduce() functions?
Python | filter(), map(), and reduce() Functions
- filter() function accepts two arguments, a function and an iterable, where each element of the iterable is filtered through the function to test if the item is accepted or not.
>>> set(filter(lambda x:x>4, range(7))) # {5, 6}
-
map() function calls the specified function for each item of an iterable and returns a list of result
>>> set(map(lambda x:x**3, range(7))) # {0, 1, 64, 8, 216, 27, 125}
-
reduce() function reduces a sequence pair-wise, repeatedly until we arrive at a single value..
>>> reduce(lambda x,y:y-x, [1,2,3,4,5]) # 3
Let’s understand this:
2-1=1
3-1=2
4-2=2
5-2=3Hence, 3.
What is a namedtuple?
Python | namedtuple
A namedtuple will let us access a tuple’s elements using a name/label. We use the function namedtuple() for this, and import it from collections.
>>> from collections import namedtuple
#format
>>> result=namedtuple('result','Physics Chemistry Maths')
#declaring the tuple
>>> Chris=result(Physics=86,Chemistry=92,Maths=80)
>>> Chris.Chemistry
# 92
Write a code to add the values of same keys in two different dictionaries and return a new dictionary.
We can use the Counter method from the collections module
from collections import Counter
dict1 = {'a': 5, 'b': 3, 'c': 2}
dict2 = {'a': 2, 'b': 4, 'c': 3}
new_dict = Counter(dict1) + Counter(dict2)
print(new_dict)
# Print: Counter({'a': 7, 'b': 7, 'c': 5})
Python In-place swapping of two numbers
Python | In-place swapping of two numbers
>>> a, b = 10, 20
>>> print(a, b)
10 20
>>> a, b = b, a
>>> print(a, b)
20 10
Reversing a String in Python
Python | Reversing a String
>>> x = 'PythonWorld'
>>> print(x[: : -1])
dlroWnohtyP
Python join all items of a list to convert into a single string
Python | Join all items of a list to convert into a single string
>>> x = ["Python", "Online", "Training"]
>>> print(" ".join(x))
Python Online Training
python return multiple values from functions
Python | Return multiple values from functions
>>> def A():
return 2, 3, 4
>>> a, b, c = A()
>>> print(a, b, c)
2 3 4
Python Print String N times
Python | Print String N times
>>> s = 'Python'
>>> n = 5
>>> print(s * n)
PythonPythonPythonPythonPython
Python check the memory usage of an object
Python | Check the memory usage of an object
>>> import sys
>>> x = 100
>>> print(sys.getsizeof(x))
28