# Τεκμηρίωση του Django - 1.10.7

# Πηγαίος κώδικας για το django.contrib.postgres.forms.hstore

    import json

    from django import forms
    from django.core.exceptions import ValidationError
    from django.utils import six
    from django.utils.translation import ugettext_lazy as _

    __all__ = ['HStoreField']

    class HStoreField(forms.CharField):
        """
        A field for HStore data which accepts dictionary JSON input.
        """
        widget = forms.Textarea
        default_error_messages = {
            'invalid_json': _('Could not load JSON data.'),
            'invalid_format': _('Input must be a JSON dictionary.'),
        }

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

        def to_python(self, value):
            if not value:
                return {}
            if not isinstance(value, dict):
                try:
                    value = json.loads(value)
                except ValueError:
                    raise ValidationError(
                        self.error_messages['invalid_json'],
                        code='invalid_json',
                    )

            if not isinstance(value, dict):
                raise ValidationError(
                    self.error_messages['invalid_format'],
                    code='invalid_format',
                )

            # Cast everything to strings for ease.
            for key, val in value.items():
                value[key] = six.text_type(val)
            return value

        def has_changed(self, initial, data):
            """
            Return True if data differs from initial.
            """
            # For purposes of seeing whether something has changed, None is
            # the same as an empty dict, if the data or initial value we get
            # is None, replace it w/ {}.
            initial_value = self.to_python(initial)
            return super(HStoreField, self).has_changed(initial_value, data)