Django Admin: JSONField default empty dict wont save in admin

问题

in my model defn i have

from django.contrib.postgres.fields import JSONField
.....
.......
.........

media_data=JSONField(default=dict)

I created a default admin

When i attempt to save without touching the field, i get a this field is required error.

It looks like a form validation issue because I can programatically save the model instance from code without issue.

Why is this happening?
have i missed something silly?

回答1:

1. What happening. when dive into the source code. we can see the following call stack:

    1) form.is_valid() 
       ->form.full_clean()
        -->form._clean_fields()
         ---> self.cleand_data[name] = field.clean(value)
    2) field.clean(value)
        -> self.to_python(value)
        -> self.validate(value)

when look into the source code ,you can find that,it's mainly because the empty_values check.

# These values, if given to validate(), will trigger the self.required check.
EMPTY_VALUES = (None, '', [], (), {})

as you can see the empty dict {} is as an empty value for JSONField. so it will raise Error.

2. What can we do? the Solution would be to customize the models.JSONField and forms.JSONField like below.

forms.py

from django.contrib.postgres import forms

class MyJSONField(forms.JSONField):
    empty_values = [None, "", [], ()]

db/fields.py

class MyJSONField(JSONField):
    def formfield(self, **kwargs):
        from ..forms import MyJSONField

        return super().formfield(**{"form_class": MyJSONField, **kwargs})

回答2:

Depending on your requirements, consider to use blank and/or null.

media_data=JSONField(blank=True, null=True)

回答3:

This caused problems for me recently, though with django-mysql rather than postgres and in a custom ModelForm rather than the admin interface.

I ended up overriding my model's save() method:

from django_mysql.models import JSONField

class yourModel(model):
    media_data=JSONField(default=dict, blank=True)

    def clean(self, *args, **kwargs):
        if self.media_data is None:
            self.media_data = "{}"

    def save(self, *args, **kwargs):
        self.clean()
        super().save(*args, **kwargs)

回答4:

i have similar problem previously. adding required=False in your form field will solve the problem.

class YourForm(forms.ModelForm):
    media_data = SimpleArrayField(JSONField(), required=False, widget=forms.Textarea, delimiter='|')

来源：https://stackoverflow.com/questions/55147169/django-admin-jsonfield-default-empty-dict-wont-save-in-admin