Python MongoDB Update

In database management, keeping your data current is crucial. MongoDB provides robust methods to update documents, and Python’s pymongo library makes it easy to perform these updates programmatically. At The Coding College, we simplify such tasks to help you efficiently manage your database.

Prerequisites

Before you proceed, ensure:

  1. Python Installed: Get Python from python.org.
  2. MongoDB Installed: Download MongoDB from mongodb.com.
  3. pymongo Installed: Install it using: 
pip install pymongo

Updating Documents in MongoDB

MongoDB provides two primary methods to update documents:

  1. update_one(): Updates the first document that matches a query.
  2. update_many(): Updates all documents that match a query.

Syntax

Update One Document

collection.update_one(filter, update, upsert=False)
  • filter: A query object specifying the condition.
  • update: The new values to set, increment, or modify.
  • upsert (optional): Creates a new document if no match is found.

Update Multiple Documents

collection.update_many(filter, update, upsert=False)

Examples

Example 1: Update One Document

Update the first document where the name field is “John”:

import pymongo

# Connect to MongoDB
client = pymongo.MongoClient("mongodb://localhost:27017/")
db = client["mydatabase"]
collection = db["customers"]

# Update one document
query = {"name": "John"}
new_values = {"$set": {"city": "New York"}}

result = collection.update_one(query, new_values)
print(f"Matched: {result.matched_count}, Modified: {result.modified_count}")

Example 2: Update Multiple Documents

Update all documents where the status is “active” to set status to “inactive”:

# Update multiple documents
query = {"status": "active"}
new_values = {"$set": {"status": "inactive"}}

result = collection.update_many(query, new_values)
print(f"Matched: {result.matched_count}, Modified: {result.modified_count}")

Example 3: Increment a Field

Increment the age field by 1 for all documents:

# Increment age by 1
query = {}
increment = {"$inc": {"age": 1}}

result = collection.update_many(query, increment)
print(f"Matched: {result.matched_count}, Modified: {result.modified_count}")

Example 4: Use upsert

If no document matches the query, create a new one:

# Upsert example
query = {"name": "Alice"}
new_values = {"$set": {"age": 30, "city": "Boston"}}

result = collection.update_one(query, new_values, upsert=True)
print(f"Matched: {result.matched_count}, Upserted ID: {result.upserted_id}")

Common Update Operators

MongoDB provides several operators for updates:

  1. $set: Sets the value of a field.
  2. $inc: Increments a field by a specified value.
  3. $unset: Removes a field.
  4. $push: Adds an item to an array.
  5. $pull: Removes items from an array.

Exercises

  1. Update Age: Write a script to set the age of all users named “Tom” to 40.
  2. Bulk Update: Increment the salary of all employees in “HR” by 500.
  3. Array Updates: Add a new skill to the skills field for all employees.

Error Handling

Handle Update Errors

try:
    query = {"name": "NonExistent"}
    update = {"$set": {"city": "Unknown"}}
    result = collection.update_one(query, update)
    if result.matched_count == 0:
        print("No matching document found.")
    else:
        print("Document updated successfully.")
except Exception as e:
    print(f"An error occurred: {e}")

Common Issues

  1. No Matching Documents:
    • If no document matches the query, matched_count will be 0.
  2. Invalid Update Syntax:
    • Ensure your update object uses valid MongoDB operators like $set or $inc.
  3. Accidental Updates:
    • Double-check your query to avoid unintentional changes to multiple documents.

Why Learn MongoDB Updates with Python?

Effective document updates are essential for maintaining a dynamic and relevant database. Python’s pymongo makes the process intuitive, allowing for flexible and scalable operations.

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