Updating and Deleting Data

Introduction

Welcome to the fifth lesson in our course. In this lesson, we will focus on how to update and delete items in a NoSQL database . Being able to modify and remove data is essential for maintaining accurate and up-to-information in your applications. You will learn how to update specific fields in existing records, delete individual records, and efficiently remove multiple records at once. These skills are fundamental for managing data in any NoSQL environment.

Updating Fields in Firestore Documents

To update data in Firestore, you can modify specific fields within a document without replacing the entire document. This is done by referencing the document you want to update and specifying the fields and new values. Here is an example of updating the content field of a document in the UserPosts collection, where the document ID is john_post1: Pythonfrom google.cloud import firestore db = firestore.Client() # Reference to the document doc_ref = db.collection('UserPosts').document('john_post1') # Update the 'content' field doc_ref.update({ 'content': 'Updated World!' }) This operation changes only the specified field, leaving the other fields in the document unchanged. You must provide the correct document reference to ensure the update is applied to the intended item.

Deleting Documents in Firestore

To remove a document from a collection in Firestore, you use the delete() method on the document reference. This will permanently remove the document and all its fields from the database. Here is how you would delete a document with the ID john_post2 from the UserPosts collection: Python from google.cloud import firestore db = firestore.Client() # Reference to the document doc_ref = db.collection('UserPosts').document('john_post2') # Delete the document doc_ref.delete() Once deleted, the document and its data cannot be recovered. Make sure to double-check the document reference before performing a delete operation.

Deleting Multiple Documents At Once

Firestore allows you to perform batch operations, which can include deleting multiple documents in a single request. This is useful for efficiently removing several documents at once. Here is an example of deleting two documents from the UserPosts collection using a batch operation: Python from google.cloud import firestore db = firestore.Client() batch = db.batch() # References to the documents to delete doc_ref1 = db.collection('UserPosts').document('john_post1') doc_ref2 = db.collection('UserPosts').document('anna_post1') # Add delete operations to the batch batch.delete(doc_ref1) batch.delete(doc_ref2) # Commit the batch operation batch.commit() Batch operations help reduce the number of separate requests and can make your data management tasks more efficient.

Join the 1M+ learners on CodeSignal

Be a part of our community of 1M+ users who develop and demonstrate their skills on CodeSignal

Method 1: Using the `@firestore.transactional` Decorator

Python

from google.cloud import firestore

db = firestore.Client()

@firestore.transactional
def update_user_balance(transaction, user_ref, amount):
    # Read the current balance
    user_doc = user_ref.get(transaction=transaction)
    current_balance = user_doc.get('balance')
    
    # Check if sufficient funds
    if current_balance >= amount:
        # Update the balance
        new_balance = current_balance - amount
        transaction.update(user_ref, {'balance': new_balance})
        return True
    else:
        return False

# Usage
user_ref = db.collection('Users').document('john_doe')
transaction = db.transaction()
success = update_user_balance(transaction, user_ref, 50)

from google.cloud import firestore

db = firestore.Client()

@firestore.transactional
def update_user_balance(transaction, user_ref, amount):
    # Read the current balance
    user_doc = user_ref.get(transaction=transaction)
    current_balance = user_doc.get('balance')
    
    # Check if sufficient funds
    if current_balance >= amount:
        # Update the balance
        new_balance = current_balance - amount
        transaction.update(user_ref, {'balance': new_balance})
        return True
    else:
        return False

# Usage
user_ref = db.collection('Users').document('john_doe')
transaction = db.transaction()
success = update_user_balance(transaction, user_ref, 50)

The @firestore.transactional decorator automatically handles transaction retry logic. When you use this decorator:

Automatic Retries: Firestore will automatically retry the transaction up to 5 times if it encounters contention (when another transaction modifies the same documents simultaneously)
Rollback Triggers: The transaction will be rolled back and retried when:
- Another transaction modifies documents that your transaction has read
- Network errors occur during the transaction
- Temporary server errors are encountered
Failure Conditions: The transaction will fail permanently (no more retries) when:
- All 5 retry attempts are exhausted
- Application logic errors occur (like Python exceptions in your code)
- Documents don't exist when expected
- Security rules violations happen

This automatic retry mechanism means your transactional function may execute multiple times, so ensure your logic is idempotent (safe to run multiple times with the same result).

Method 2: Using Transaction Objects Directly

Python

from google.cloud import firestore

db = firestore.Client()

def transfer_funds(from_user_id, to_user_id, amount):
    transaction = db.transaction()
    
    @firestore.transactional
    def update_in_transaction(transaction):
        # References to both user documents
        from_ref = db.collection('Users').document(from_user_id)
        to_ref = db.collection('Users').document(to_user_id)
        
        # Read both balances
        from_doc = from_ref.get(transaction=transaction)
        to_doc = to_ref.get(transaction=transaction)
        
        from_balance = from_doc.get('balance')
        to_balance = to_doc.get('balance')
        
        # Check sufficient funds
        if from_balance >= amount:
            # Update both balances atomically
            transaction.update(from_ref, {'balance': from_balance - amount})
            transaction.update(to_ref, {'balance': to_balance + amount})
            return True
        else:
            return False
    
    return update_in_transaction(transaction)

from google.cloud import firestore

db = firestore.Client()

def transfer_funds(from_user_id, to_user_id, amount):
    transaction = db.transaction()
    
    @firestore.transactional
    def update_in_transaction(transaction):
        # References to both user documents
        from_ref = db.collection('Users').document(from_user_id)
        to_ref = db.collection('Users').document(to_user_id)
        
        # Read both balances
        from_doc = from_ref.get(transaction=transaction)
        to_doc = to_ref.get(transaction=transaction)
        
        from_balance = from_doc.get('balance')
        to_balance = to_doc.get('balance')
        
        # Check sufficient funds
        if from_balance >= amount:
            # Update both balances atomically
            transaction.update(from_ref, {'balance': from_balance - amount})
            transaction.update(to_ref, {'balance': to_balance + amount})
            return True
        else:
            return False
    
    return update_in_transaction(transaction)

This example demonstrates a funds transfer between two users, which is a classic use case for transactions. The function creates a transaction object and defines a nested transactional function that reads both users' current balances, verifies sufficient funds, and then atomically updates both accounts. This approach ensures that either both the debit and credit operations succeed together, or neither happens at all, preventing scenarios where money could be lost or created due to partial updates.

Introduction

Updating Fields in Firestore Documents

Deleting Documents in Firestore

Deleting Multiple Documents At Once

Join the 1M+ learners on CodeSignal

Understanding Firestore Transactions

Why Transactions Matter

Using Transactions in Firestore

Method 1: Using the `@firestore.transactional` Decorator

Method 2: Using Transaction Objects Directly

When to Use Transactions

Summary and Upcoming Practices