Refactors You Need To Know for Your Django Project | by Rico Tadjudin | Apr, 2022

Photograph by Chris Ried on Unsplash

** Notice: This text is written for the needs of a person evaluation for CSUI’s Software program Engineering Venture Course 2022. **

Refactoring is likely one of the most necessary practices you will need to do for your entire tasks. Even when your tasks are comparatively small and easy, refactoring code is all the time inspired and is the most effective observe for extra readable, easy, and cleaner code. On this article, I’ll be displaying you some issues that may be refactored if you’re utilizing Django (particularly Django REST Framework) as your framework of alternative! Let’s go!

You Need to Know These Refactors!
(Django Models) Custom Model Manager
(Django Models) Select Related and Prefetch Related
(Django REST Views) Class Based Views with Mixins and Generics

In these examples, I’ll be utilizing these fashions that I’ve made for my Software program Engineering Venture Course 2022.

(Django Fashions) Customized Mannequin Supervisor

In keeping with Django Documentations, “Mannequin Managers in Django is an interface by means of which database question operations are supplied to Django fashions.”

You won’t notice this, however you most likely have used Django’s mannequin supervisor when utilizing Django Fashions. If you write Time period.objects.all(), the ‘objects’ in the course of the default supervisor are supplied to all fashions by Django.

Right here’s the place issues get fascinating: you may make your personal customized mannequin supervisor that may do different issues handy to you and your mannequin.

For instance, if I wish to get all programs in a selected time period (i.e., time period “2021/2022–1”), and I need them to be ordered by the course’s title, then usually we’d most likely write this:


To be sincere with you, there isn’t a large downside with this, however in the event you’ll be utilizing this actual filtering and ordering a number of instances in your code, you’ll see that you simply’re going to repeat the code time and again. This lengthy filter and ordering can cut back the readability of your code. Issues can enhance in the event you use a customized mannequin supervisor and QuerySet, like this for instance:

Don’t overlook to assign the brand new customized supervisor to the mannequin. You may overwrite the default ‘objects’ supervisor or create a brand new customized supervisor with a distinct title. For this, I’ll be overwriting the default ‘objects’ supervisor.

With this, you are able to do the identical factor as earlier than by scripting this:


You might see that it’s extra readable than the code earlier than, and it’s less complicated with out repeating the .filter and .order_by. Certain, this instance could not appear to enhance the code a lot, however you need to use customized managers for no matter you need and wish. This may considerably enhance your code readability and stop you from repeating your code.

(Django Fashions) Choose Associated and Prefetch Associated

Chances are you’ll not know but about select_relatedand prefetch_related, however these capabilities supplied by Django are actually helpful. For my part, a must have for improved database question efficiency. It is because when you’ve gotten already queried a bunch of objects to a QuerySet, and then you definately wish to entry its overseas key object’s attribute, Django will question the database once more for each overseas key attribute of each object you’re calling.

Take a guess: if the code under is executed, what number of queries does Django make to the database?

programs = Course.objects.filter(credit score=4) #for instance returns 2 objfor course in programs:
print(course.time period.title)

Chances are you’ll assume that it must be one, proper? It ought to question the database when Course.objects.filter is executed? I’m sorry, however that reply is inaccurate. The appropriate reply is there can be three database question calls.

How? Clearly, the primary question is on the filter. After that, as a result of there are two Course objects in queryset, programs, and the code asks for a overseas key’s attribute, (course.time period.title), then for each iteration of the for loop, Django will make a further question name to the database.

It is because the preliminary Course.objects.filter doesn’t have the data of the time period’s title. Think about in the event you’re doing 1,000 iterations or extra. You’ll be querying the database 1,000 instances for this alone.

To stop this from occurring, you need to use select_relatedand prefetch_relatedto get these overseas key attributes on the preliminary filter question. You may seek for the variations between the 2, however in brief, you utilize select_relatedwhen the item attribute is a single object (like OneToOneField or a ForeignKey), whereas you utilize prefetch_relatedif you’re going to get greater than a single object or a set of issues (ManyToManyFieldsor reverse ForeignKey’s).

programs = Course.objects.filter(credit score=4).select_related("time period")for course in programs:
print(course.time period.title)

By including select_related("time period"), you’ll question all the data of the overseas key “time period” of programs objects within the first question. Due to that, Django wouldn’t want to question the database for each iteration of the for loop.

This can considerably enhance your database question efficiency (extra like stopping large quantities of database querying), and I personally assume it makes your code extra readable by explicitly telling readers you’ll need these attributes of a sure overseas key later.

(Django REST Views) Class-Primarily based Views with Mixins and Generics

** Notice: I’ll be discussing class-based views for the Django REST Framework. Class-based views for Django are a bit totally different, and you may see the Django documentation for extra data **

Class-based views are most likely already well-known by many Django customers. However for my part, you must use class-based views sparsely. For complicated views, I feel class-based views would possibly decrease readability (for many who are usually not fluent in class-based views) and lacks flexibility.

However for easy views, notably REST views in Django REST Framework (DRF), you undoubtedly ought to use class-based views with the supplied mixins and generics because it’s considerably extra easy, wants much less code, and improves readability (for others who already know class-based views).

For instance, with function-based views, I might write GetAndDeleteTermViews like this, preserving in thoughts that you must make the serializer to your mannequin first for serializing the information. On this case, I’ve named mine TermSerializer:

There’s no large downside functionally with the above code. It ought to work positive because it’s alleged to. However you’ll be able to see with extra complicated logic, it will get so much messier. There could be much more strains of code, and/or much more ifs and elifs. This could decrease the readability of your code. Right here’s the identical performance with class-based views, mixins, and generics:

As you’ll be able to see, it’s much more easy and readable. One different benefit is all of the errors that will occur (like 404 when the item doesn’t exist) are already dealt with by Django. This can take much less growth time and enhance readability for readers who’ve a fundamental understanding of class-based views.

I feel these are important refactors that you will need to take into account in your Django tasks. These are undoubtedly not all of the issues that it is advisable refactor. You need to seek for extra issues that want refactoring, however I discover lots of people new to Django are usually not conscious of issues like mannequin supervisor and select_related/prefetch_related in Django.

All the hassle you set in refactoring code will certainly repay with a extra clear, easy, readable, and improved code.

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