6/30/2025
This set of rules provides best practices for Django ORM development. It covers code organization, common patterns, performance optimization, security, testing, and tooling. It emphasizes proper directory structure, naming conventions, and avoiding anti - patterns. It also details techniques for performance, security, and how to use various tools for development, testing, and deployment.
## 1. Code Organization and Structure
### 1.1. Directory Structure Best Practices
- **Application-Centric Structure:** Organize your Django project around applications (apps), where each app represents a specific feature or module.
- **Dedicated 'models' Module:** Keep all model definitions within the `models.py` file of each app.
- **Separate Queries:** For complex queries, consider creating a `queries.py` or `managers.py` file within your app to house custom querysets and managers.
- **Consistent Naming:** Use consistent naming conventions for app and model names.
myproject/
├── myproject/
│ ├── __init__.py
│ ├── asgi.py
│ ├── settings.py
│ ├── urls.py
│ ├── wsgi.py
├── app1/
│ ├── __init__.py
│ ├── admin.py
│ ├── apps.py
│ ├── models.py
│ ├── managers.py # Custom managers and querysets
│ ├── views.py
│ ├── urls.py
│ ├── forms.py
│ ├── tests.py
│ └── migrations/
├── app2/
│ └── ...
└── manage.py
### 1.2. File Naming Conventions
- **Models:** Use singular nouns and CamelCase (e.g., `UserProfile`, `BlogPost`).
- **Fields:** Use lowercase with underscores (snake_case, e.g., `first_name`, `date_joined`).
- **Managers/Querysets:** Use descriptive names related to their functionality (e.g., `ActiveUsersManager`, `PublishedPostsQuerySet`).
- **Files:** Use lowercase with underscores (snake_case, e.g., `models.py`, `forms.py`, `urls.py`).
### 1.3. Module Organization
- **Keep Models Concise:** Limit the number of models in each app to a manageable amount (ideally under 10). If an app becomes too large, refactor it into smaller, more focused apps.
- **Avoid Circular Imports:** Be mindful of circular dependencies between models and other modules within the same app or across apps. Use string references in `ForeignKey` and `ManyToManyField` definitions to avoid immediate import requirements.
- **Utilize Abstract Base Classes:** For common fields across multiple models, define an abstract base class and inherit from it. This promotes code reuse and reduces redundancy. Don't forget to set `abstract = True` in the `Meta` class.
- **Consider Proxy Models:** Use proxy models (`proxy = True` in `Meta`) to change a model's behavior without altering the database schema. This is useful for adding methods or changing the default ordering.
### 1.4. Component Architecture
- **DRY (Don't Repeat Yourself):** Create reusable components such as custom model fields, managers, and querysets.
- **Model Mixins:** Use model mixins to add common functionality to multiple models (e.g., a mixin for soft deletion or timestamping).
- **Form Abstraction:** Create reusable form classes and widgets for data input and validation.
- **Template Tags and Filters:** Develop custom template tags and filters to simplify common tasks in templates related to model data.
### 1.5. Code Splitting Strategies
- **App-Based Splitting:** Organize models and related code within distinct Django apps.
- **Manager-Based Splitting:** Divide complex queries into custom managers and querysets.
- **Mixin-Based Splitting:** Utilize mixins to compartmentalize functionality across models.
- **Signal-Based Splitting:** Implement signals for decoupling operations, such as triggering tasks when a model is saved or deleted.
## 2. Common Patterns and Anti-patterns
### 2.1. Design Patterns
- **Repository Pattern:** Abstract data access logic behind a repository interface, allowing you to switch between different data sources without modifying the rest of your application.
- **Unit of Work Pattern:** Group multiple database operations into a single transaction to ensure atomicity and consistency.
- **Specification Pattern:** Encapsulate query logic into reusable specification objects, allowing you to combine and reuse queries across different parts of your application.
- **Model Decorators:** Use decorators to add functionality to models without modifying the original model class. Useful for things like caching calculated properties.
### 2.2. Recommended Approaches for Common Tasks
- **Filtering Data:** Use `filter()` and `exclude()` for efficient data retrieval.
- **Ordering Data:** Utilize `order_by()` to specify the order of results.
- **Aggregating Data:** Employ `aggregate()` to calculate summary statistics.
- **Creating and Updating Objects:** Use `create()` and `save()` for object manipulation.
- **Deleting Objects:** Use `delete()` for removing objects.
- **Prefetch Related:** Use `select_related` for ForeignKey and OneToOneField relationships, and `prefetch_related` for ManyToManyField and reverse ForeignKey relationships.
### 2.3. Anti-patterns and Code Smells
- **Overusing `raw()` Queries:** Prefer Django ORM methods over raw SQL queries to maintain database abstraction and security.
- **Ignoring Database Indexes:** Neglecting to add indexes to frequently queried columns can lead to significant performance bottlenecks. Use `db_index = True` and `Index` in Meta to specify indices.
- **Using `null=True` for String-Based Fields:** Avoid `null=True` for `CharField` and `TextField` fields. Use `blank=True` and an empty string (`''`) instead.
- **Creating Large Querysets without Pagination:** Avoid retrieving large datasets without pagination. Use Django's `Paginator` to break results into manageable chunks.
- **Performing Logic in Templates:** Keep templates focused on presentation. Move complex logic to views or custom template tags.
- **N+1 Query Problem:** Accessing related objects in a loop can cause the N+1 query problem. Use `select_related()` and `prefetch_related()` to mitigate this.
- **Inefficient Use of Exists/Count:** Prefer `exists()` over `count()` when simply checking for the existence of objects.
- **Unnecessary Database Hits:** Optimize data access patterns to minimize the number of database queries.
### 2.4. State Management
- **Database as Primary State:** Rely on the database as the single source of truth for application state.
- **Session Management:** Utilize Django's session framework for storing user-specific state.
- **Caching:** Implement caching strategies to reduce database load and improve response times.
- **Avoid Global Mutable State:** Minimize the use of global mutable state, as it can lead to unexpected behavior and concurrency issues.
### 2.5. Error Handling
- **Catch Database Exceptions:** Handle database exceptions (e.g., `IntegrityError`, `OperationalError`) gracefully.
- **Use Transactions:** Wrap multiple database operations in a transaction to ensure atomicity.
- **Log Errors:** Log errors and exceptions for debugging and monitoring purposes. Use `logger.exception()` to capture the traceback.
- **Custom Exception Handling Middleware:** Consider writing custom middleware to catch and handle database errors at a global level, providing user-friendly error messages.
- **Validate Data Before Saving:** Always validate data before saving it to the database to prevent errors and data inconsistencies. Use Django's built-in validators or create custom validators.
## 3. Performance Considerations
### 3.1. Optimization Techniques
- **Query Optimization:** Use `select_related` and `prefetch_related` to reduce the number of database queries.
- **Indexing:** Add indexes to frequently queried columns.
- **Caching:** Implement caching strategies for frequently accessed data.
- **Pagination:** Use pagination for large datasets.
- **Batch Operations:** Use `bulk_create`, `bulk_update` and `bulk_delete` for bulk operations.
- **Defer/Only:** use `defer` to exclude fields from the query or `only` to only include specific fields in the query.
- **Conditional Expressions:** Use `Case`, `When`, and `Value` within queries to perform conditional logic directly in the database.
### 3.2. Memory Management
- **Limit Queryset Size:** Avoid retrieving large datasets into memory. Use pagination or generators.
- **Use Generators:** For processing large datasets, use generators to process data in chunks.
- **Garbage Collection:** Understand Python's garbage collection mechanisms and how they affect memory usage.
- **Profiling:** Use profiling tools to identify memory leaks and optimize memory usage.
### 3.3. Rendering Optimization
- **Template Caching:** Cache frequently used templates to reduce rendering time.
- **Context Processors:** Minimize the data passed to templates via context processors.
- **Lazy Loading:** Use lazy loading for images and other resources to improve initial page load time. Consider using template tags like `{% static %}` and `{% get_static_prefix %}` effectively.
### 3.4. Bundle Size Optimization
- **Remove Unused Code:** Eliminate unused models, fields, and queries.
- **Optimize Static Files:** Minify and compress static files (CSS, JavaScript, images).
- **Code Splitting:** Split JavaScript and CSS into smaller chunks for efficient loading.
### 3.5. Lazy Loading
- **Load Related Data on Demand:** Use lazy loading for related data to improve initial performance. Consider using Django Rest Framework serializers with `depth=0` and selectively increasing the depth when needed.
- **Database Views:** Create database views for complex queries to improve performance.
- **QuerySet Iterators:** Instead of converting large querysets into lists, iterate over them using `.iterator()` for memory efficiency.
## 4. Security Best Practices
### 4.1. Common Vulnerabilities and Prevention
- **SQL Injection:** Prevent SQL injection by using Django ORM methods instead of raw SQL queries. Always parameterize your queries.
- **Cross-Site Scripting (XSS):** Sanitize user input and escape output in templates.
- **Cross-Site Request Forgery (CSRF):** Use Django's CSRF protection mechanisms.
- **Authentication and Authorization:** Implement robust authentication and authorization mechanisms.
- **Session Hijacking:** Secure sessions using HTTPS and appropriate session settings.
### 4.2. Input Validation
- **Use Django Forms:** Employ Django Forms for validating user input.
- **Sanitize User Input:** Sanitize user input to prevent XSS attacks.
- **Validate Data Types:** Validate data types to prevent database errors.
- **Limit Input Length:** Restrict input length to prevent buffer overflows.
- **Custom Validators:** Create custom validators for complex validation logic.
- **Consider using DRF Serializers:** Use Django Rest Framework Serializers to add an extra layer of validation to your models and data.
### 4.3. Authentication and Authorization
- **Use Django's Built-in Authentication:** Leverage Django's built-in authentication framework.
- **Implement Role-Based Access Control (RBAC):** Define roles and permissions for different user types.
- **Enforce Password Policies:** Enforce strong password policies.
- **Use Multi-Factor Authentication (MFA):** Implement MFA for sensitive accounts.
- **Rate Limiting:** Implement rate limiting to prevent brute-force attacks.
### 4.4. Data Protection
- **Use HTTPS:** Use HTTPS to encrypt data in transit.
- **Encrypt Sensitive Data:** Encrypt sensitive data at rest.
- **Store Passwords Securely:** Store passwords using a strong hashing algorithm (e.g., bcrypt, Argon2).
- **Regularly Back Up Data:** Regularly back up your database.
- **Audit Logging:** Implement audit logging to track user activity and data changes.
### 4.5. Secure API Communication
- **Use API Keys:** Use API keys for authenticating API requests.
- **Implement OAuth 2.0:** Implement OAuth 2.0 for secure API authorization.
- **Validate API Input:** Validate API input to prevent injection attacks.
- **Rate Limiting:** Implement rate limiting to prevent API abuse.
- **API Versioning:** Use API versioning to manage changes to your API.
## 5. Testing Approaches
### 5.1. Unit Testing
- **Test Model Methods:** Unit test model methods to ensure they behave as expected.
- **Test Custom Managers:** Unit test custom managers to verify their query logic.
- **Test Validators:** Unit test validators to ensure they correctly validate data.
- **Mock Database Dependencies:** Use mocking to isolate model tests from the database.
### 5.2. Integration Testing
- **Test Views and Models:** Integrate test views and models to ensure they work together correctly.
- **Test Forms and Models:** Integrate test forms and models to verify data validation and persistence.
- **Use Test Fixtures:** Use test fixtures to create consistent test data.
- **Test Database Interactions:** Test database interactions to ensure they are efficient and correct.
### 5.3. End-to-End Testing
- **Test User Workflows:** End-to-end test user workflows to ensure they are functional and user-friendly.
- **Test API Endpoints:** End-to-end test API endpoints to ensure they are secure and functional.
- **Use Selenium or Similar Tools:** Use Selenium or similar tools for automating end-to-end tests.
- **Test Across Different Browsers:** Test across different browsers to ensure compatibility.
### 5.4. Test Organization
- **Organize Tests by App:** Organize tests by app to improve maintainability.
- **Use Descriptive Test Names:** Use descriptive test names to clearly indicate what is being tested.
- **Follow a Consistent Test Structure:** Follow a consistent test structure to improve readability.
- **Use Test Runners:** Use test runners to automate test execution.
### 5.5. Mocking and Stubbing
- **Mock Database Queries:** Mock database queries to isolate tests from the database.
- **Stub External Dependencies:** Stub external dependencies to control test environments.
- **Use Django's `override_settings` Decorator:** Use Django's `override_settings` decorator to modify settings during tests.
- **Use `patch` for Mocking:** Use `unittest.mock.patch` for mocking objects and functions.
## 6. Common Pitfalls and Gotchas
### 6.1. Frequent Mistakes
- **Not Using Indexes:** Forgetting to add indexes to frequently queried columns.
- **Overusing `null=True`:** Using `null=True` for string-based fields.
- **Ignoring Database Transactions:** Not using database transactions for critical operations.
- **Creating Large Querysets:** Creating large querysets without pagination.
- **Performing Logic in Templates:** Performing logic in templates instead of views.
- **N+1 Query Problem:** Not addressing the N+1 query problem.
### 6.2. Edge Cases
- **Unicode Handling:** Handling Unicode characters correctly.
- **Time Zones:** Dealing with time zones accurately.
- **Concurrency Issues:** Managing concurrency issues in multi-threaded environments.
- **Database-Specific Differences:** Handling database-specific differences.
### 6.3. Version-Specific Issues
- **Deprecated Features:** Being aware of deprecated features and migrating to newer alternatives.
- **Compatibility Changes:** Handling compatibility changes between Django versions.
### 6.4. Compatibility Concerns
- **Python Version:** Ensuring compatibility with the supported Python versions.
- **Database Compatibility:** Ensuring compatibility with the chosen database.
- **Third-Party Libraries:** Ensuring compatibility with third-party libraries.
### 6.5. Debugging
- **Use Django's Debug Toolbar:** Use Django's Debug Toolbar for profiling and debugging.
- **Inspect Database Queries:** Inspect database queries to identify performance bottlenecks.
- **Log Errors and Exceptions:** Log errors and exceptions for debugging purposes.
- **Use a Debugger:** Use a debugger to step through code and inspect variables.
- **Read Stack Traces Carefully:** Read stack traces carefully to understand the source of errors.
## 7. Tooling and Environment
### 7.1. Recommended Development Tools
- **IDE:** PyCharm, VS Code with Python extension.
- **Database Client:** pgAdmin, MySQL Workbench, DB Browser for SQLite.
- **Virtual Environment Manager:** virtualenv, pipenv, conda.
- **Debug Toolbar:** Django Debug Toolbar.
- **Profiling Tools:** cProfile, line_profiler.
### 7.2. Build Configuration
- **Use a Virtual Environment:** Use a virtual environment to isolate project dependencies.
- **Specify Dependencies:** Specify dependencies in a `requirements.txt` or `Pipfile`.
- **Use a Build System:** Use a build system (e.g., Make, Fabric) to automate build tasks.
- **Configure Static File Handling:** Configure static file handling correctly for production.
### 7.3. Linting and Formatting
- **Use a Linter:** Use a linter (e.g., pylint, flake8) to enforce code style.
- **Use a Formatter:** Use a formatter (e.g., black, autopep8) to automatically format code.
- **Configure Editor Integration:** Configure editor integration to automatically lint and format code on save.
- **Follow PEP 8:** Adhere to PEP 8 style guidelines.
### 7.4. Deployment
- **Use a Production-Ready Web Server:** Use a production-ready web server (e.g., Gunicorn, uWSGI).
- **Use a Reverse Proxy:** Use a reverse proxy (e.g., Nginx, Apache) to handle static files and load balancing.
- **Use a Database Server:** Use a dedicated database server (e.g., PostgreSQL, MySQL).
- **Configure Caching:** Configure caching to improve performance.
- **Secure Deployment:** Secure the deployment environment with appropriate firewalls and security settings.
- **Use Environment Variables:** Store sensitive configuration data (e.g., database passwords, API keys) in environment variables.
### 7.5. CI/CD Integration
- **Use a CI/CD System:** Use a CI/CD system (e.g., Jenkins, Travis CI, GitLab CI) to automate testing and deployment.
- **Run Tests Automatically:** Run tests automatically on every commit.
- **Deploy Automatically:** Deploy automatically on successful builds.
- **Use Infrastructure as Code:** Use infrastructure as code (e.g., Terraform, Ansible) to automate infrastructure provisioning.
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By consistently applying these best practices, you'll establish a robust foundation for building high-quality Django applications that are performant, maintainable, and secure.