Admin form escapes postgres JSONField on ValidationError

[Rubén Díaz]

To reproduce this bug, let's assume we have this model:

class TestModel(models.Model):
    test_url = models.URLField()  # I've chosen URLField as an example but the specific type of field is irrelevant for this issue
    json_field = JSONField(default={})

The model is added to the admin site the standard way (admin.site.register()) so that we can add content easily. Now, if you go and submit the following:

test_url → test
json_field → {"hello": "hola"}

It'll trigger an expected ValidationError since it's not a valid URL. When the form is rendered and presented back to the user, the test_url will show the incorrect URL while the json_field will look like this: "{\"hello\": \"hola\"}". If the user corrects the test_url and submits the form again, the json_field that's being stored in the DB will be the escaped one.

I can't say if this only happens with admin forms or any form (e.g. model forms) since I have no time to run proper tests, but I hope this is enough to track down the issue.

[Tim Graham]

Duplicate of #25532

[Laurynas Riliskis]

I am running Django 2 and encounter the same problem. The same results are obtained is called though the admin interface.

>>> p = JSONTest.objects.get(instance="4550d7f3a28c4081af5b3ff5ac62ab60")
>>> p.data
'{}'
>>> p.save()
>>> p = JSONTest.objects.get(instance="4550d7f3a28c4081af5b3ff5ac62ab60")
>>> p.data
'"{}"'
>>> p.save()
>>> p = JSONTest.objects.get(instance="4550d7f3a28c4081af5b3ff5ac62ab60")
>>> p.data
'"\\"{}\\""'
>>> p.save()
>>> p = JSONTest.objects.get(instance="4550d7f3a28c4081af5b3ff5ac62ab60")
>>> p.data
'"\\"\\\\\\"{}\\\\\\"\\""'