pretty-print json in JSONField form field

[David Szotten]

Makes manual editing nicer

(json.dumps with indent)

[Tim Graham]

I'm not convinced this belongs in the form field. I think such logic belongs in a custom widget.

[David Szotten]

ah, that's a good suggestion

[David Szotten]

that solves my problem so happy to close, unless you think such a widget would make sense to include? (maybe to niche)

[Tim Graham]

I agree.

[minusf]

I would normally agree with a custom widget approach, however json is special.
In my understanding a custom widget would have to munge through the vanilla unindented
json.dumps() value returned by contrib.postgres.forms.JSONField.prepare_value().

django/contrib/postgres/forms/jsonb.py:

    def prepare_value(self, value):
        if isinstance(value, InvalidJSONInput):
            return value
        return json.dumps(value)

Probably meaning an ugly hack of json.loads() then json.dumps() round trip inside the custom widget...

For my use cases a simple json.dumps(value, indent=2) would already make
a huge difference in readability, no custom widget needed and problem solved.
Overriding that however is a mess...

models.py:

from django.contrib.postgres.fields import JSONField
from django.contrib.postgres.forms import JSONField as JSONFormField
from django.core.serializers.json import DjangoJSONEncoder


# XXX not exported from postgres.forms :/
class InvalidJSONInput(str):
    pass


# XXX JSONFormField would be a better name for forms.JSONField  :/
class IndentedJSONFormField(JSONFormField):

    def prepare_value(self, value):
        if isinstance(value, InvalidJSONInput):
            return value
        return json.dumps(value, indent=2)


class IndentedJSONField(JSONField):

    def formfield(self, **kwargs):
        return super().formfield(**{
            'form_class': IndentedJSONFormField,
            **kwargs,
        })


class Data(models.Model):
    data = IndentedJSONField(encoder=DjangoJSONEncoder, default=dict)