django-bulk-hooks 0.1.96

Hook-style hooks for Django bulk operations like bulk_create and bulk_update.

django-bulk-hooks

⚡ Bulk hooks for Django bulk operations and individual model lifecycle events.

django-bulk-hooks brings a declarative, hook-like experience to Django's bulk_create, bulk_update, and bulk_delete — including support for BEFORE_ and AFTER_ hooks, conditions, batching, and transactional safety. It also provides comprehensive lifecycle hooks for individual model operations.

✨ Features

• Declarative hook system: @hook(AFTER_UPDATE, condition=...)
• BEFORE/AFTER hooks for create, update, delete
• Hook-aware manager that wraps Django's bulk_ operations
• NEW: HookModelMixin for individual model lifecycle events
• Hook chaining, hook deduplication, and atomicity
• Class-based hook handlers with DI support
• Support for both bulk and individual model operations
• NEW: Safe handling of related objects to prevent RelatedObjectDoesNotExist errors

🚀 Quickstart

pip install django-bulk-hooks

Define Your Model

from django.db import models
from django_bulk_hooks.models import HookModelMixin

class Account(HookModelMixin):
    balance = models.DecimalField(max_digits=10, decimal_places=2)
    # The HookModelMixin automatically provides BulkHookManager

Create a Hook Handler

from django_bulk_hooks import hook, AFTER_UPDATE, Hook
from django_bulk_hooks.conditions import WhenFieldHasChanged
from .models import Account

class AccountHooks(HookHandler):
    @hook(AFTER_UPDATE, model=Account, condition=WhenFieldHasChanged("balance"))
    def log_balance_change(self, new_records, old_records):
        print("Accounts updated:", [a.pk for a in new_records])
    
    @hook(BEFORE_CREATE, model=Account)
    def before_create(self, new_records, old_records):
        for account in new_records:
            if account.balance < 0:
                raise ValueError("Account cannot have negative balance")
    
    @hook(AFTER_DELETE, model=Account)
    def after_delete(self, new_records, old_records):
        print("Accounts deleted:", [a.pk for a in old_records])

Advanced Hook Usage

class AdvancedAccountHooks(HookHandler):
    @hook(BEFORE_UPDATE, model=Account, condition=WhenFieldHasChanged("balance"))
    def validate_balance_change(self, new_records, old_records):
        for new_account, old_account in zip(new_records, old_records):
            if new_account.balance < 0 and old_account.balance >= 0:
                raise ValueError("Cannot set negative balance")
    
    @hook(AFTER_CREATE, model=Account)
    def send_welcome_email(self, new_records, old_records):
        for account in new_records:
            # Send welcome email logic here
            pass

🔒 Safely Handling Related Objects

One of the most common issues when working with hooks is the RelatedObjectDoesNotExist exception. This occurs when you try to access a related object that doesn't exist or hasn't been saved yet.

The Problem

# ❌ DANGEROUS: This can raise RelatedObjectDoesNotExist
@hook(AFTER_CREATE, model=Transaction)
def process_transaction(self, new_records, old_records):
    for transaction in new_records:
        # This will fail if transaction.status is None or doesn't exist
        if transaction.status.name == "COMPLETE":
            # Process the transaction
            pass

The Solution

Use the safe_get_related_attr utility function to safely access related object attributes:

from django_bulk_hooks.conditions import safe_get_related_attr

# ✅ SAFE: Use safe_get_related_attr to handle None values
@hook(AFTER_CREATE, model=Transaction)
def process_transaction(self, new_records, old_records):
    for transaction in new_records:
        # Safely get the status name, returns None if status doesn't exist
        status_name = safe_get_related_attr(transaction, 'status', 'name')
        
        if status_name == "COMPLETE":
            # Process the transaction
            pass
        elif status_name is None:
            # Handle case where status is not set
            print(f"Transaction {transaction.id} has no status")

Complete Example

from django.db import models
from django_bulk_hooks import hook
from django_bulk_hooks.conditions import safe_get_related_attr

class Status(models.Model):
    name = models.CharField(max_length=50)

class Transaction(HookModelMixin, models.Model):
    amount = models.DecimalField(max_digits=10, decimal_places=2)
    status = models.ForeignKey(Status, on_delete=models.CASCADE, null=True, blank=True)
    category = models.ForeignKey('Category', on_delete=models.CASCADE, null=True, blank=True)

class TransactionHandler:
    @hook(Transaction, "before_create")
    def set_default_status(self, new_records, old_records=None):
        """Set default status for new transactions."""
        default_status = Status.objects.filter(name="PENDING").first()
        for transaction in new_records:
            if transaction.status is None:
                transaction.status = default_status
    
    @hook(Transaction, "after_create")
    def process_transactions(self, new_records, old_records=None):
        """Process transactions based on their status."""
        for transaction in new_records:
            # ✅ SAFE: Get status name safely
            status_name = safe_get_related_attr(transaction, 'status', 'name')
            
            if status_name == "COMPLETE":
                self._process_complete_transaction(transaction)
            elif status_name == "FAILED":
                self._process_failed_transaction(transaction)
            elif status_name is None:
                print(f"Transaction {transaction.id} has no status")
            
            # ✅ SAFE: Check for related object existence
            category = safe_get_related_attr(transaction, 'category')
            if category:
                print(f"Transaction {transaction.id} belongs to category: {category.name}")
    
    def _process_complete_transaction(self, transaction):
        # Process complete transaction logic
        pass
    
    def _process_failed_transaction(self, transaction):
        # Process failed transaction logic
        pass

Best Practices for Related Objects

1. Always use safe_get_related_attr when accessing related object attributes in hooks
2. Set default values in BEFORE_CREATE hooks to ensure related objects exist
3. Handle None cases explicitly to avoid unexpected behavior
4. Use bulk operations efficiently by fetching related objects once and reusing them

class EfficientTransactionHandler:
    @hook(Transaction, "before_create")
    def prepare_transactions(self, new_records, old_records=None):
        """Efficiently prepare transactions for bulk creation."""
        # Get default objects once to avoid multiple queries
        default_status = Status.objects.filter(name="PENDING").first()
        default_category = Category.objects.filter(name="GENERAL").first()
        
        for transaction in new_records:
            if transaction.status is None:
                transaction.status = default_status
            if transaction.category is None:
                transaction.category = default_category
    
    @hook(Transaction, "after_create")
    def post_creation_processing(self, new_records, old_records=None):
        """Process transactions after creation."""
        # Group by status for efficient processing
        transactions_by_status = {}
        
        for transaction in new_records:
            status_name = safe_get_related_attr(transaction, 'status', 'name')
            if status_name not in transactions_by_status:
                transactions_by_status[status_name] = []
            transactions_by_status[status_name].append(transaction)
        
        # Process each group
        for status_name, transactions in transactions_by_status.items():
            if status_name == "COMPLETE":
                self._batch_process_complete(transactions)
            elif status_name == "FAILED":
                self._batch_process_failed(transactions)

This approach ensures your hooks are robust and won't fail due to missing related objects, while also being efficient with database queries.