JSONFieldFormMixin for Django ModelForm with JSON field

forms.py

# the mixin

class JSONFieldFormMixin(object):
    """
    Given that a model has some kind of TextField ``json_storage_field`` with
    a string of JSON formatted data inside, this mixin adds handling of this
    field to a ModelForm.

    It will read the text field, convert to Python dict, fill the form fields
    that are given via ``json_fields`` and on saving will write this back to
    the JSON field, updating just the fields that are included in the ModelForm.

    Attributes:
        json_storage_field: which field of the model holds the JSON data, should only be text

    Attributes on form.Meta:
        json_fields: the fields to read and save, need to be model fields defined on ModelForm
    """
    json_storage_field = "meta"

    def get_from_json_field(self):
        return json.loads(getattr(self.instance, self.json_storage_field) or "{}")

    def __init__(self, *args, **kwargs):
        super(JSONFieldFormMixin, self).__init__(*args, **kwargs)
        if self.instance:
            meta_json = self.get_from_json_field()
            for field in self.Meta.json_fields:
                if meta_json.get(field):
                    self.fields[field].initial = meta_json.get(field)

    def save(self, *args, **kwargs):
        meta_json = self.get_from_json_field()
        for field in self.Meta.json_fields:
            meta_json[field] = self.cleaned_data[field]
        setattr(self.instance, self.json_storage_field, json.dumps(meta_json))
        return super(JSONFieldFormMixin, self).save(*args, **kwargs)


# example model


class Solution(models.Model):
    name = models.CharField(max_length=255)
    description = models.TextField(blank=True)
    url = models.URLField("URL", blank=True)
    meta = models.TextField(blank=True)
    
    
# example ModelForm    
    

class SolutionForm(JSONFieldFormMixin, ModelForm):
    currency = forms.CharField(required=False)
    info = forms.CharField(required=False)

    class Meta:
        model = Solution
        json_fields = ('currency', 'info')
        fields = ('name', 'description', 'url') + json_fields