Unable to enter json in django admin

Question

In my model I have the following field -

data_fields = ArrayField(models.JSONField(null=True, blank=True), blank=True, null=True)

In order to test this out, I entered the following in the data_field in the django admin -

[{"key": "name", "label": "Name"}, {"key": "amount", "label": "Amount"}]

But I get an error saying

Item 1 in the array did not validate: Enter a valid JSON.
Item 2 in the array did not validate: Enter a valid JSON.
Item 3 in the array did not validate: Enter a valid JSON.
Item 4 in the array did not validate: Enter a valid JSON.

I only get this error if there are multiple key-value pairs in the JSON. If there is only one JSON element with one key-value pair, it works. If there are multiple elements in the array, or there are multiple key-value pairs in the JSON field, I get the error above.

Why is this happening, and how do I fix it?

Answer 1

This is one of the many reasons not to use an ArrayField or JSONField in the first place ^{[django-antipatterns]}. ArrayFields are, as far as I know, not very well supported in databases nor in Django, and that results in all sorts of querying problems, and problems with forms. Here for example it will split on a comma, so the first item looks like {"key": "name", that is indeed not valid JSON, the proof of this behavior is that it sees four elements, not two. It thus does not know when to split, and as a result passes incorrect items to the JSON deserializer.

That being said, why not just use a JSONField ^[Django-doc], after all, a list is a JSON blob, so using:

data_fields = models.JSONField(null=True, blank=True, default=list)

But still, if the structure is fixed, like the JSON blob seems to be, I would advise using an inline:

class Parent(models.Model):
    pass


class ParentDataField(models.Model):
    parent = models.ForeignKey(
        Parent, related_name='data_fields', on_delete=models.CASCADE
    )
    key = models.CharField(max_length=128)
    label = models.CharField(max_length=128)

in fact, we even can ensure that for the same parent, the key only occurs at most once:

class Parent(models.Model):
    pass


class ParentDataField(models.Model):
    parent = models.ForeignKey(
        Parent, related_name='data_fields', on_delete=models.CASCADE
    )
    key = models.CharField(max_length=128)
    label = models.CharField(max_length=128)

    class Meta:
        constraints = [
            models.UniqueConstraint(
                fields=('parent', 'key'), name='unique_key_per_parent'
            )
        ]

and then work with an inline:

from django.contrib import admin


class ParentDataFieldInline(admin.TabularInline):
    model = ParentDataField


class ParentAdmin(admin.ModelAdmin):
    inlines = [
        ParentDataFieldInline,
    ]