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Working with Django Models in Python: Best Practices

The Django framework provides a versatile toolset for managing your code and data. However, there are many strategies you can follow to build more stable products. Following best practices, Django models can become more secure, maintainable, and scalable. 

As a backend engineer at Django Stars, I’ve accumulated a lot of knowledge about Django and Python. This article discusses some of the Django models management best practices that can help save you time and effort.

These are some Django models best practices, including everyday tips and advanced techniques that I use to manage them. They range from fine-tuning fields and simplifying queries to improving security for object relationships.

Let’s start with the correct Django models name conventions. Although simple, these are invaluable for maintaining your databases.

A model should be named with a singular noun, representing a single entity. This makes understanding the relationship between models easier and avoids confusion.

Long model names are difficult to remember and type. Opt for concise names: for instance, use Feedback instead of CustomerFeedbackSurveyResponse.

Django models follow Python-based Pascal case naming conventions, meaning each word in the name should start with a capital letter and contain no underscores.

Abbreviations often introduce needless ambiguity. Instead of writing Addr, use the complete term Address.

Always avoid terms that are reserved by Django or Python. Don’t name models using terms like object, class, or get.

Model names should be aligned with the application name without duplicating it. If the app name is Blog, model names could include Post, Comment, and Tag.

Careful naming of relationship fields (special Django models field types establishing connections between different data models) contributes to a cleaner and more maintainable Django codebase.

A ManyToManyField should include a plural noun that reflects the related model. For instance, the field name could be Categories if a Product model has a ManyToManyField to a Category model.

A OneToOneField represents a one-to-one relationship and should be named using a singular noun that reflects the related model.

I always avoid vague or ambiguous names, as it helps prevent confusion when multiple relationship fields exist between the same models.

Always use lowercase letters and underscores for Django model fields names to prevent case sensitivity issues with database backends. For example, full_name instead of FullName.

Avoid using the same name for a related_name argument and a field within one class. On the other hand, having the same field name in different classes doesn’t affect the model.

Using the choices arguments correctly improves data integrity in Django models. It creates a central repository of predefined values, enforces model validation, and helps avoid hardcoding the values in the views. You can also use choices to limit user input per value to prevent unwanted queries.

When composing a list of tuples, use choices to define the valid values and human-readable names. This simple method minimizes the risk of inconsistent data entry.

While choices can be used with any field type, I prefer using CharField (string field storing text values) and IntegerField (numeric fields for integer values). Using choices with CharField can avoid using cryptic codes or abbreviations, while IntegerField helps avoid arbitrary numbers.

Defining the values as Constants or Enums helps make choices more maintainable and easily updatable. It also helps avoid hardcoding choice values throughout the codebase, which leads to many headaches and errors. For example, instead of using (‘A’, ‘Available’), use (AVAILABLE, ‘Available’), where AVAILABLE is a defined constant.

Choices don’t enforce constraints at the database level. While choices validate and display field values in forms and admin interfaces, their use can cause unexpected behavior. It’s better to ensure data integrity via other database-level methods like constraints, triggers, and custom validators.

The choices argument doesn’t alter the database schema, meaning you don’t need to perform database migrations when choices are added or removed. However, removal might cause errors in existing records that use old or removed choices. The solution might be to write a script that updates all records or deletes ones that are no longer relevant.

In new database models, both null and blank are set to False. These two values are easy to confuse, but they’re quite different.

In Django, the null argument indicates whether a database column can store null values. Setting null=False means the price column cannot have null values in the database. Meanwhile, the default value of null is False for most field types, except for the ForeignKey, OneToOneField, and ManyToManyField.

The blank argument is a Boolean validation-related value determining if the field can be empty. For example, if a Product model has a field named description that is a TextField, setting blank=True means that the description field can be left blank or empty in forms, indicating that the product has no description.

A common misconception is that setting null=True on a CharField or TextField would allow no data. However, both null and an empty string would signify no data, creating needless ambiguity. It’s better to default to an empty string for these field types.

The Meta class is a nested class inside a model class that provides metadata and configuration options for the model.

I explicitly name the model and the fields. This can be done with verbose_name and verbose_name_plural — human-readable names for the model used in the admin interface and error messages. Another way is to use app_label to specify the app’s name for migrations.

Setting the ordering attribute in your model’s Meta class helps organize how objects will be listed by default. For instance, ordering = (‘name’, ‘-price’) sorts objects by name in ascending order and by price in descending order. However, be cautious — sorting can impact performance. If you need it, consider adding an index for quicker retrievals.

Using the db_table attribute lets you define the name of the database table for your model, like db_table = ‘shop_product’. This is a handy way to avoid table name clashes in your database.

Employing UniqueConstraint instead of the older unique_together helps enforce uniqueness in multi-column fields. This ensures there can’t be two instances of the model with identical values. It works at the database level, adding an extra layer of integrity.

The indexes option can speed up queries. By using indexes instead of deprecated index_together, you can improve query performance for specific combinations of fields (like names, categories, and statuses).

With the constraints attribute, you can specify custom database-level constraints using models that inherit from models.BaseConstraint. For example, a check constraint can be applied to the price field to ensure it’s always greater than zero.

Indexes can speed up the read operations on the database, such as filtering, sorting, or joining.

Setting unique=True on a model field ensures its value will be one-of-a-kind within the database table. This indexing is handled automatically by Django. For instance, if your Product model features a SKU field, making it unique prevents duplicate SKUs.

I use db_index=True for often queried fields with a wide range of unique values. For example, applying it to a Product model will speed up the queries that filter by this field.

• Indexes can add overhead, as you must update them whenever a record is added, updated, or deleted.
• Indexes consume disk space; for example, if your model’s name field has a max length of 255 characters, indexing uses 255 bytes for every record.
• Indexes require regular maintenance, as they become fragmented or unbalanced over time due to frequent changes in the status values.

Custom managers can significantly streamline your query processes but require deliberate configuration and usage. 

You can use custom managers to allow for tailored query sets to chain data retrieval. If your Product model has a custom manager called available with a method by_category, you can filter for available books with Product.available.by_category(‘books’).

Custom managers from parent models don’t pass down automatically in case of multi-table inheritance. For instance, if a Book model inherits from a Product model with an available custom manager, the Book model would lack this manager unless explicitly declared.

If the related model uses a custom manager, related objects may not be applied automatically. You should name them explicitly to avoid issues. Meanwhile, the associated objects are accessed easily if your models are related through a ForeignKey or OneToOneField.

If you have several custom managers, Django will default to the first one defined. The Product model uses available and discontinued managers to query objects by default. To access the discontinued ones, you need to specify them.

You can use Product.objects.all() to get all products as a query set. However, this default is overridden if you use custom managers. Be mindful of this, especially if your codebase expects the default manager to be present.

By adopting these practices, you can proactively handle database exceptions.

By using transaction.atomic(), you ensure that all database operations are executed consistently. If exceptions like IntegrityError or OperationalError occur, the database will rollback, preserving its integrity.

Always log critical details such as the type of exception, its message, and the traceback. I recommend using methods like logger.exception() to capture full metadata, including timestamps.

Middleware can collect database exceptions that happen in any view function or other class in a centralized way. This is useful for logging or returning responses after database errors.

Use Django’s separate databases and test cases to detect database issues preemptively. These features cover a wide variety of testing scenarios and support rollback.

Check model fields with built-in or custom validators to catch inconsistencies before they reach the database. This can help to avoid IntegrityError or DatabaseError category errors that might occur due to invalid values or decimal places.

There are a few ways to calculate the number of records for a particular model in Django, but I prefer ModelName.objects.count().

The ModelName.objects.count() method leverages the SQL COUNT function to calculate the number of rows. It doesn’t fetch the data for calculations, so you get information without extra processing overhead.

Meanwhile, len(ModelName.objects.all()) fetches all the data from the database into Python before doing the count. This can be especially burdensome if you’re dealing with large datasets.

Getting an ID directly from the related field (book.author.id) can be inefficient. It requires loading the related object from the database.

I recommend using book.author_id instead of book.author.id. In Django, each ForeignKey field automatically comes with an _id attribute that directly references the ID of the related object. In a model with an author ForeignKey field linked to an Author model, author_id can access or update the author’s identity without invoking an additional database query. 

I used the exists() query set method to find objects in models efficiently. Unlike the filter() method, exists() doesn’t retrieve all the matching data. It also avoids generating exceptions that get() if there are no matches or multiple matches.

Model inheritance speeds up engineering by letting you reuse common fields, extend the functionality of existing models, and organize them.

Consider using abstract base classes when you have common fields in multiple models. An abstract base class won’t create its own database table but serves as a centralized repository for shared attributes. This simplifies code maintenance, as changes to the base class propagate to all inheriting models.

Proxy models help change a model’s behavior without altering the underlying database schema. To create a proxy model, simply set proxy =True in the model’s Meta class.

I use multi-table inheritance only for specialized fields or methods of some subclasses. Other than that, it’s best to avoid it, as it creates a table for each model in the inheritance chain, thus complicating queries.

Django automatically creates a primary key field named ID for each model, but you can define a custom primary key field. 

The primary_key=True lets you appoint a unique value as the primary key. For instance, if you have a Product model with an SKU (Stock Keeping Unit), setting primary_key=True on this field eliminates the default ID field.

Using sequential IDs generated by an AutoField exposes you to the risk of inadvertently leaking system information. It’s better to use random, unique, and hard-to-guess IDs. For example, UUIDField, as your primary key, generates a universally unique identifier for each object.

Use appropriate relationship fields to enforce data consistency and validation rules for the related objects.

It’s essential to specify on_delete behavior to specify what should happen when a referenced object gets deleted. Django offers several options like models.CASCADE, models.PROTECT, and models.SET_NULL for enhanced control.

Employing database transactions helps you ensure that either all or none of the operations are committed. If any exception occurs within the code block, all the database operations will be rolled back.

A Many-to-Many relationship generates an extra table that contains pairs of primary keys from the related models. This table may also store additional relationship data. You should set permissions for this additional table to limit unauthorized access or changes.

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Following efficient practices lays a foundation for successful projects. It lets you optimize your team’s performance without acquiring technical debt. But the tips we explored here are just a sample.

At Django Stars, we like to go beyond the basics. If you’re interested, we can share even more Django tools to improve your web development projects.

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Frequently Asked Questions

What common field types can I use to define a Django model?

You can use a range of field types: CharField for text, IntegerField for integers, DateField for date values, and ForeignKey for relational data. Each type serves a specific purpose and helps in optimizing database storage, retrieval, and updating.

How to improve the performance of Django models?

To optimize your models, I recommend using appropriate field types, Django naming conventions, and constraints for attributes. You should also use indexing techniques to speed up queries. Opt for the _id attribute when dealing with ForeignKey fields to reduce database queries. In addition, use exists() instead of filter() for quick object checks.

What are Django security best practices when working with models?

Avoid using raw SQL queries or unsafe methods that expose your data to SQL injection attacks. Use non-predictable IDs (like UUIDField), define appropriate permissions and authentication mechanisms, and validate your data before saving.

What are some common mistakes when working with Django models?

Common errors include inefficient naming, improper field handling, and incorrect query set methods for object checks. The lack of specified on_delete behavior in relationship fields is another pitfall. Make sure each model class handles only one type of data and functionality. Dividing your logic into smaller, manageable functions can also prevent your models from becoming overburdened.

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