Django 1.9 JSONField order_by

问题:

I have the following django model that contains JSONField:

class RatebookDataEntry(models.Model):
    data = JSONField(blank=True, default=[])
    last_update = models.DateTimeField(auto_now=True)

    class Meta:
        verbose_name_plural = 'Ratebook data entries'

And data field contains this json:

{
    "annual_mileage": 15000, 
    "description": "LEON DIESEL SPORT COUPE", 
    "body_style": "Coupe", 
    "range_name": "LEON", 
    "co2_gkm_max": 122, 
    "manufacturer_name": "SEAT"
}

Can I sort queryset by one of the data fields? This query doesn't work.

RatebookDataEntry.objects.all().order_by("data__manufacturer_name")

回答1:

As Julien mentioned ordering on JSONField is not yet supported in Django. But it's possible via RawSQL using PostgreSQL functions for jsonb. In OP's case:

from django.db.models.expressions import RawSQL
RatebookDataEntry.objects.all().order_by(RawSQL("data->>%s", ("manufacturer_name",)))

回答2:

Since Django 1.11, django.contrib.postgres.fields.jsonb.KeyTextTransform can be used instead of RawSQL

from django.contrib.postgres.fields.jsonb import KeyTextTransform

qs = RatebookEntry.objects.all()
qs = qs.annotate(manufacturer_name=KeyTextTransform('manufacturer_name', 'data'))
qs = qs.order_by('manufacturer_name')
# or...
qs = qs.order_by('-manufacturer_name')

On Django 1.10, you'll have to subclass KeyTransform yourself:

from django.contrib.postgres.fields.jsonb import KeyTransform

class KeyTextTransform(KeyTransform):
    operator = '->>'
    nested_operator = '#>>'
    _output_field = TextField()

Note: the difference between KeyTransform and KeyTextTransform is that KeyTransform will return the JSON representation of the object, whereas KeyTextTransform will return the value of the object.

For example, if data is {"test": "stuff"}, KeyTextTransform will return 'stuff', whereas KeyTransform will return '"stuff"' (which can be parsed by json.loads)

回答3:

Following Daniil Ryzhkov answer and Eugene Prikazchikov comment, you should be able to sort ASC and DESC on JSON data fields without annotating your queryset, by using both RawSQL and OrderBy. Also, you can perform case insensitive sorting by adding LOWER:

from django.db.models.expressions import RawSQL, OrderBy

RatebookDataEntry.objects.all().order_by(OrderBy(RawSQL("LOWER(data->>%s)", ("manufacturer_name",)), descending=True))

To compare integers fields, you can cast as integer:

RatebookDataEntry.objects.all().order_by(OrderBy(RawSQL("cast(data->>%s as integer)", ("annual_mileage",)), descending=True))

回答4:

This is an upcoming feature which has already been added and will be released in Django 2.1, expected release of August 2018.

See https://code.djangoproject.com/ticket/24747 and https://github.com/django/django/pull/8528 for details.

回答5:

The documentation does not mention this possibility. It seems you cannot use order_by based on a JSONfield for the moment.