Introduction to Django-Filter and How to Implement Tricky Requirements

Django-Filter is a very useful third-party library that makes great use of Django ORM's features. You can extend existing APIs with very little code to implement various filtering functions~

Scenario

Part of the Model definition code. You can see that the requirement model includes these three fields: keyword keyword, region region, and requirement status require_status

class Require(models.Model):
    """需求"""
    keyword = models.CharField('需求关键字', max_length=1000, blank=True)
    region = models.ForeignKey(Region, verbose_name='落地实施区域', null=True, on_delete=models.SET_NULL)
    require_status = models.IntegerField('需求进行状态', choices=RequireStatusChoice.choices)

Next is the ViewSet code. In DRF, after simple route configuration you can get the requirement list, but real-world scenarios definitely require more than this

class RequireViewSet(viewsets.ModelViewSet):
    """需求记录"""
    serializer_class = RequireSerializer
    queryset = Require.objects.all()

The product needs many features. For this requirement module specifically, we need:

• Search requirements by keyword
• Filter requirements by implementation region
• Filter requirements by requirement progress status

If we were using Java, we'd definitely have to dutifully write a few extra lines of code to implement this. But! Life is short, I use Python!

How could we Python users possibly yield to implementing such a simple feature? When it's time to be lazy, we must be lazy. If there's no way to be lazy, we still have to force ourselves to be lazy hhh~

Simple Usage of Django-Filter

Let's see how we implement this with Django-Filter. First, install Django-Filter:

pip install django-filter

Add it to settings.py:

INSTALLED_APPS = [
    ...
    'django_filters',
]

Then just configure it in the ViewSet:

from django_filters.rest_framework import DjangoFilterBackend

class RequireViewSet(viewsets.ModelViewSet):
    """需求记录"""
    serializer_class = RequireSerializer
    queryset = Require.objects.all()
    filter_backends = [DjangoFilterBackend, SearchFilter]
    # 参与分类筛选的字段
    filter_fields = ['require_status', 'region']
    # 参与搜索的字段: search=关键词
    search_fields = ['keyword']

After configuration, you can filter and search on top of the original API. Assume the endpoint is: http://127.0.0.1/require/

Search

http://127.0.0.1/require/?search=关键词

Filter by Region

http://127.0.0.1/require/?region=1

Filter by Requirement Status

http://127.0.0.1/require/?require_status=2

The result is perfect. Just simple configuration can implement so many features. That's the benefit of being lazy (standing on the shoulders of giants). These CRUD features don't really involve much technical skill anyway—the authors of the framework and third-party libraries have already implemented them for us, so we can just use them~

But then the frontend folks came up with a new requirement: the requirement status require_status needs to filter requirements with multiple statuses at once, for example filtering requirements with status numbers 2-9 at the same time... This is a pain. Django-Filter only supports one by default. What to do...

But don't worry. I believe no problem can stump my Stack Overflow, so I searched a bunch of keywords, tried four or five methods provided by helpful netizens, and sure enough found the best solution...

Filtering Multiple Values at Once

First, define a custom Filter. Here I use commas to split each parameter. The code is as follows:

from django_filters import Filter,FilterSet

class ListFilter(Filter):
    def filter(self, qs, value):
        if not value:
            return qs
        # For django-filter versions < 0.13, use lookup_type instead of lookup_expr
        self.lookup_expr = 'in'
        values = value[0:1000].split(',')
        return super(ListFilter, self).filter(qs, values)

class RequireStatusFilter(FilterSet):
    require_statuses = ListFilter(field_name='require_status')
    class Meta:
        from apps.require.models import Require
        model = Require
        fields = ['require_statuses', 'region']

Then modify our ViewSet. You can see that filter_fields is no longer needed, because it's already defined in RequireStatusFilter

class RequireViewSet(viewsets.ModelViewSet):
    """需求记录"""
    serializer_class = RequireSerializer
    queryset = Require.objects.all()
    permission_classes = [permissions.IsAuthenticated]
    filter_backends = [DjangoFilterBackend, SearchFilter]
    filter_class = RequireStatusFilter
    search_fields = ['keyword']

How to Use

Absolutely delightful

http://127.0.0.1/require/?region=1&require_status=1,2,3,4,5,6,7,8,9

Gossip

Finally, a bit of gossip: today the father of Python tweeted that he joined Microsoft, and the father of Delphi/C#/TypeScript posted congratulations in the comments, hahaha

References

• Stack Overflow question: https://stackoverflow.com/questions/31029792/djangofilterbackend-with-multiple-ids
• Official documentation: https://django-filter.readthedocs.io/