dj-drf-utils 1.2.0

Useful functions and classes for Django and Django Rest Framework

dj-drf-utils

This package provides useful functions and classes to be used in Django projects, specially when working with Django Rest Framework. Below are some further explation about how to use this package and what each module inside it does.

The examples on this documentation are about movies and cinemas, having entities like Movie, Cinema, Room, and MovieSession.

Installation

First, run:

pip install dj-drf-utils

That's it!

helpers.py

This module provides three useful functions. Two of them are a more powerful and versatille version of get_object_or_404 and get_list_or_404, and the other is a handy shortcut.

get_object_or_error

Almost the same as django.shortcuts.get_object_or_404, but can raise any custom error class you want, allowing you to return more precise error messages. Another advantage of using this helper function, is that it prevents your application from crashing. For instance, in case you want to get an object by it's primary key, and it is of type uuid, but another data type is provided in the url, it will not crash, unlike the standard get_object_or_404. It expects the following arguments:

• klass -> The model that will be used for the query
• exception -> An error class inheriting from rest_framework.exceptions.APIException. If no exception is provided, then the standard django.http.Http404 class is used.
• **kwargs -> Keyword arguments representing all fields that should be used for the search, as many as you please.

For instance, in case you want to get a Room of a Cinema:

# exceptions.py

from rest_framework.exceptions import APIException, status


class CinemaNotFoundError(APIException):
    status_code = status.HTTP_404_NOT_FOUND
    default_detail = "Cinema not found"


class RoomNotFoundError(APIException):
    status_code = status.HTTP_404_NOT_FOUND
    default_detail = "Room not found in this cinema"

# request endpoint

"/cinemas/<cinema_id>/rooms/<room_id>/"

# views.py

from dj_drf_utils.helpers import get_object_or_error


cinema = get_object_or_error(Cinema, CinemaNotFoundError, pk=self.kwargs['cinema_id'])
room = get_object_or_error(Room, RoomNotFoundError, pk=self.kwargs['room_id'], cinema=cinema)

Note that in case a room id is valid, but the cinema id is not, an appropriated message will be returned. In case you would use get_object_or_404, you would get just a "Not found.". Having more than one lookup field, get_object_or_error makes much clearer what is the problem.

I highly encorage you to have a quick look at the source code, it's quite a simple concept.

---

get_list_or_error

Almost the same as django.shortcuts.get_list_or_404, but can raise any custom error class you want, allowing you to return more precise error messages. Another advantage of using this helper function, is that it prevents your application from crashing. For instance, in case you want to get a list, filtering it by some foreign key field, which is of type uuid, but another data type is provided in the url, it will not crash, unlike the standard get_list_or_404. Also, this function gives you the possiblity of not raising an exception when no values are found, so you could just return an empty list. It expects the following arguments:

• klass -> The model that will be used for the query
• exception -> An error class inheriting from rest_framework.exceptions.APIException. If no exception is provided, then the standard django.http.Http404 class is used.
• accept_empty -> A boolean argument, which defaults to False. When provided, determines if an empty result is acceptable or if it should raise exception.
• **kwargs -> Keyword arguments representing all fields that should be used for the search, as many as you please.

For instance, in case you want to list all MovieSessions of a Room in a Cinema:

# exceptions.py

from rest_framework.exceptions import APIException, status


class NoMovieSessionsError(APIException):
    status_code = status.HTTP_404_NOT_FOUND
    default_detail = "This room has no scheduled movie sessions"

# request endpoint

"/cinemas/<cinema_id>/rooms/<room_id>/movie-sessions/"

# views.py

from dj_drf_utils.helpers import get_object_or_error, get_list_or_error


cinema = get_object_or_error(Cinema, CinemaNotFoundError, pk=self.kwargs['cinema_id'])
room = get_object_or_error(Room, RoomNotFoundError, pk=self.kwargs['room_id'], cinema=cinema)
movie_sessions = get_list_or_error(MovieSession, NoMovieSessionsError, room=room)

I highly encorage you to have a quick look at the source code, it's quite a simple concept.

---

set_and_destroy

This function basically sets a new list of values in a foreign key field and erases any previous values that were related to klass. For it to work, you must set null=True in your model, otherwise, the values will not be subsitituted, they will only be added. It accepts the following parameters:

• klass -> The model on the side 1 of a 1:N relationship, the owner of the relation, in which the new values will be set
• attr -> A string version of the attribute corresponding to the related_name value in the foreign key field
• value -> A list (or any other iterable), containing new created instances of related_klass
• related_klass -> The model on the side N of a 1:N relationship, the one having the foreign key field
• **kwargs -> Keyword arguments used in a filter to determine which objects should be destroyed. It could be really anything, but usually you will want it to be something like klass=None, so that all objects that are no part of the relationship anymore can be descarded.

For instance, a Movie may have many Videos related to it, like teasers and trailers. In case you want to update a Movie, reseting its Videos:

# models.py

class Movie(models.Model):
    ...


class Video(models.Model):
    id = models.UUIDField(primary_key=True, editable=False, default=uuid4)
    title = models.CharField(max_length=127)
    url = models.URLField()

    movie = models.ForeignKey(Movie, on_delete=models.CASCADE, related_name="videos", null=True)

# serializers.py

from dj_drf_utils.helpers import set_and_destroy


class MovieSerializer(serializers.ModelSerializer):
    ...

    def update(self, instance: Movie, validated_data: dict):
      ...

      videos_data = validated_data.pop("videos", None)
      if videos_data:
          videos = [
            Video.get_or_create(**video, movie=instance)[0]
            for video in videos_data
          ]
          set_and_destroy(
              klass=instance,
              attr="videos",
              value=videos,
              related_klass=Video,
              movie=None,
          )

In the example above, we are first getting or creating video instances, in order to reuse the ones passed in the body of the request that may already be in our db. Each video can only be related to one movie, since it doesn't make sense that two movies have the same trailer or teaser. So when assigning this new list of videos to a movie, the set_and_destroy function safely deletes all videos having their movie foreign key equal to None.

I highly encorage you to have a quick look at the source code, it's quite a simple concept.

---

bulk_get_or_create

Despite the name of this function, it does not translate into a single database hit, unfortunatelly. But it is still better than a loop executing Model.objects.get_or_create in every iteration.

That's because this function combines filters and the bulk_create method. Django querysets are lazy, but in this function they are evaluated on every iteration. However, in the end only one INSERT query is performed.

---

Important!

Django's Model.objects.bulk_create method returns a list of newly created instances without ids when working with SQLite. Please, make sure to use PostgreSQL to avoid problems.

---

It expects the following parameters:

• klass -> The model whose values will be retrieved or created
• values -> A list of dictionaries having key value pairs demanded by klass
• only_create -> A boolean value. Defaults to False. In case you don't care about getting existing values, and just wants to create them, then you can set this arguments to True. It will result in just one database hit.
• kwargs -> Key value pairs with extra fields you want to use for filtering/creating instances of klass. It can be useful for foreign key fields

Usage example:

# serializers.py

from dj_drf_utils.helpers import bulk_get_or_create, set_and_destroy


class MovieSerializer(serializers.ModelSerializer):
    # ...

    def create(self, validated_data: dict) -> Movie:
        # ...

        videos_data = validated_data.pop("videos")

        # ...

        bulk_get_or_create(Video, videos_data, movie=movie)

        # ...

    def update(self, instance: Movie, validated_data: dict) -> Movie:
        # ...

        videos = validated_data.pop("videos", None)

        # ...

        if videos:
            set_and_destroy(
                klass=instance,
                attr="videos",
                value=bulk_get_or_create(Video, videos, movie=instance),
                related_klass=Video,
                movie=None,
            )

        # ...

Note that in the update method, we are combining set_and_destroy with bulk_get_or_create. That's totally a thing.

I highly encourage you to have a look at the source code, so that you can better understand what's happening under the hood. It's not complicated.

mixins.py

This module provides useful mixins to be used in Django Rest Framework generic views and viewsets.

SerializerByMethodMixin

This mixin overrides the get_serializer_class method of generic views. It's purpose is to dinamically define which serializer to use, depending on the request method. For this to be possible, a new class property should be set, it is:

• method_serializers -> It should be a dictionary having it's keys with the names of http methods and values as the serializer classes corresponding to each method. If the request method does not match any of the dict keys, it will return the value of self.serializer_class.

Below is an example:

# views.py

from dj_drf_utils.mixins import SerializerByMethodMixin


class MyBeautifulGenericView(SerializerByMethodMixin, ListCreateAPIView):
    queryset = MyWonderfulModel.objects.all()
    serializer_class = MyDefaultSerializer
    method_serializers = {
        "GET": MySerialzerToUseInGetRequests,
    }

---

SerializerByActionMixin

This mixin overrides the get_serializer_class method of viewsets. It's purpose is to dinamically define which serializer to use, depending on the viewset action. For this to be possible, a new class property should be set, it is:

• action_serializers -> It should be a dictionary having it's keys with the names of viewset actions and values as the serializer classes corresponding to each action. If the viewset action does not match any of the dict keys, it will return the value of self.serializer_class.

Below is an example:

# views.py

from dj_drf_utils.mixins import SerializerByActionMixin


class MyBeautifulViewSet(SerializerByActionMixin, ModelViewSet):
    queryset = MyWonderfulModel.objects.all()
    serializer_class = MyDefaultSerializer
    action_serializers = {
        "create": MySerializerToUseInCreateActions,
        "update": MySerialzerToUseInUpdateActions,
        "partial_update": MySerialzerToUseInPartialUpdateActions,
    }

---

SerializerByDetailActionsMixin

This mixin overrides the get_serializer_class method of viewsets. It's purpose is to dinamically define which serializer to use, depending on the viewset action. If it is a detail action, that is, one of retrieve, update, partial_update and destroy, then self.detail_serializer_class will be returned. Else, the default self.serializer_class is used. For this to be possible, a new class property should be set, it is:

• detail_serializer_class -> It's value should be a serializer class. This property defines which serializer to use in detail actions.

Below is an example:

# views.py

from dj_drf_utils.mixins import SerializerByDetailActionsMixin


class MyBeautifulViewSet(SerializerByDetailActionsMixin, ModelViewSet):
    queryset = MyWonderfulModel.objects.all()
    serializer_class = MyDefaultSerializer
    detail_serializer_class = MyDetailSerializer

---

SerializerBySafeActionsMixin

This mixin overrides the get_serializer_class method of viewsets. It's purpose is to dinamically define which serializer to use, depending on the viewset action. If it is a safe action, then self.safe_serializer_class will be returned. Else, the default self.serializer_class is returned. A safe action is an action listed in the safe_actions class property. For this to be possible, a new class property should be set, it is:

• safe_serializer_class -> Its value should be a serializer class. This property defines which serializer to use in safe actions.

You can totally customize what is a "safe action". For that, you could change the value of self.safe_actions.

• safe_actions -> It should be a list[str], which each item representing a viewset action, considered safe for that viewset. The default value is ["list", "retrieve"]

Below is an example:

# views.py

from dj_drf_utils.mixins import SerializerBySafeActionsMixin


class MyBeautifulViewSet(SerializerBySafeActionsMixin, ModelViewSet):
    queryset = MyWonderfulModel.objects.all()
    serializer_class = MyDefaultSerializer
    safe_serializer_class = MySafeSerializer

managers.py

This module provides a custom user manager as a shortcut for whoever wants to customize django's authentication system to use a different field instead of username for login. It can be really anything, like email, phone, cpf, etc.

CustomUserManager

A custom user manager that inherits from django.contrib.auth.models.BaseUserManager. Its purpouse in life is mainly to provide an easy and simple way to implement a login and register system that expects another field instead of username.

But what if you desired to customize your users in a way that other info is also required for user creation? No problem, this class is highly customizable.

Instead of having to override the create and create_superuser methods of BaseUserManager, you can inherit from CustomUserManager and then simply set some class properties at your will. They work as follows:

• auth_field_name -> Defaults to "email". Defines what is the name of the field that should be used for login (besides password, of course). Note that this field must exist in your user model, having a unique constraint.
• user_is_staff -> Defaults to False. Defines the starting staff status of newly created users
• user_start_active -> Defaults to True. Defines if a user account should start in active state. In cases where users have to confirm their account in some way before getting access, you may wish to set this property to False
• super_is_staff -> Defaults to True. Defines the starting staff status of newly created superusers
• super_start_active -> Defaults to True. Defines if a superuser account should start in active state. Usually you'll want this value to be True, but you're totally free to change it, depending on your needs.
• required_fields -> Defaults to []. It should be a list[str]. This property defines which fields are required to be provided upon user creation, besides self.auth_field_name and password. The fields is_staff, is_superuser and is_active should also not be present in this list. It is worth noting that all fields defined here, must also be defined in your user model. Otherwise, a ValidationError is raised.

Below is an example of how you may customize the behaviour of this class:

# managers.py

from dj_drf_utils.managers import CustomUserManager


class MyOwnUserManager(CustomUserManager):
    user_start_active = False
    required_fields = ["first_name", "last_name"]

In order to implement a login with email feature, for instance, you have to make some minor changes to your user model. Below are some settings that may come in handy for you to define in your model:

# models.py

from .managers import MyOwnUserManager
from django.db import models
from django.contrib.auth.models import AbstractUser


class MyUser(AbstractUser):
    email = models.EmailField(unique=True)

    username = None

    objects = MyOwnUserManager()

    USERNAME_FIELD = objects.auth_field_name
    REQUIRED_FIELDS = objects.required_fields

The email property is defined as unique, since it's gonna be used for login (as per the USERNAME_FIELD property). The objects property may be either the standard dj_drf_utils.managers.CustomUserManager or your own manager that inherits from it. In the example above, we are using our own user manager, with some minor customizations. REQUIRED_FIELDS refer to the fields you are prompted when creating a superuser (it must not include the value defined for USERNAME_FIELD or "password"). Defining it to objects.required_fields prevents you from making mistakes and being redundant. Note that in the example above we are droping the username column, but that's not necessary if you still want to have a username in your user model.

action_patterns.py

Viewsets have the advantage of abstracting away the work of defining routes explicitly, but routers have some limits. They can only go to a certain depth in producing urls.

For instance, let's imagine a simple application, where you have Bands and Albums. In case you wish to list all Albums of a Band, you could make a request to an enpoint like /bands/<band_id>/albums/. That's totally possible with routers. But what if you want a detail route for an Album of a Band? A route like /bands/<band_id>/albums/<album_id>/ would make sense, right? But routers aren't able to go to such an extent. And you could totally imagine bigger urls in real, bigger applications.

So defining our routes manually gives us a lot more control. Everything comes with a tradeoff though. When manually defining routes for generic views, you can easily assign each view class to their routes, using the as_view method. But viewsets are different. One viewset class can be assigned to more than one route. So for that to work, you've gotta do something like this.

In order to simplify things, and abstract away some boiler plate code, this module provides the standard viewset actions mapped to their corresponding http method. Of course, you may have additional actions, customized according to your own needs. In this case, you can config them on your own. But the standard ones are all set here.

Usage example:

# urls.py

from django.urls import path
from dj_drf_utils.action_patterns import STANDARD_DETAIL_PATTERN, STANDARD_PATTERN

from . import views


cinema_view = views.CinemaViewSet.as_view(STANDARD_PATTERN)
cinema_detail_view = views.CinemaViewSet.as_view(STANDARD_DETAIL_PATTERN)

urlpatterns = [
    path("", cinema_view),
    path("<cinema_id>/", cinema_detail_view),
]

But routers are still so cool and so simple to use. So a very good alternative is drf-nested-routers. It really makes it easier to deal with all of this. The drf-nested-routers library is designed to solve exactly this problem, and even more.

admin.py

This module provides a CustomUserAdmin class. It inherits from django.contrib.auth.admin.UserAdmin. Have you ever created a custom user model, added it to admin and then realized that your users passwords were being created unhashed? Then you searched the internet and found out that django provides a UserAdmin class that does the job. But what if you customized your authentication system, and you're using another field instead of username? In this case, it throws an error, saying that there is no username field.

In order to make things easier, this module provides a class that abstracts away all the boring configurations you would need to do.

CustomUserAdmin

This class inherits from django.contrib.auth.admin.UserAdmin. It's purpose in life is to abstract away some boring configurations you may need, when you're using a custom user model. The advantage is to have the same features that Django standard UserAdmin class provides, but in a custom user model, having a field other than username used for authentication.

This class automaticaly figures out what is your user model, as long as it is pointed to by AUTH_USER_MODEL setting in settings.py. Also, it takes the care of first checking for the fields you set in your user model before referencing them. But the password field is mandatory.

Below is an usage example:

# admin.py

from dj_drf_utils.admin import CustomUserAdmin
from .models import User

admin.site.register(User, CustomUserAdmin)

In case you want to customize some kind of behaviour, you totally can, but you will have to overwrite the properties entirely. For instance, if you need to change the columns of list_display, you could do something like this:

# admin.py

from dj_drf_utils.admin import CustomUserAdmin
from .models import User

class MyOwnUserAdmin(CustomUserAdmin):
    list_display = ['id', 'email', 'first_name', 'last_name', 'birth_date', 'is_staff', 'is_superuser']

admin.site.register(User, MyOwnUserAdmin)

Not so bad.