DateTimeField does not handle empty values correctly (#3726)

[mjparker777]

Closes #3726

Added code to handle None and empty string.
Also added outputs in testing.

[jpadilla]

Like #2869 (comment) says maybe we should also check out if TimeField needs any fixing. That could be a separate PR as well.

[mjparker777]

You are correct. I updated the timefield and the test output for timefield also.

[mjparker777]

FYI - I see that someone added a string conversion in datefield:

            if (isinstance(value, str)):
                value = datetime.datetime.strptime(value, '%Y-%m-%d').date()

I think this is problematic.
First the format is very specific. It requires the order of Y m d and the - as the separator.
I dont think this should be carried into the time and datetime fields (I actually think it should be removed). This would require string conversion methods for each that would require covering all of the possible string representations for each.

The datetime, date, and time fields have options to allow the fields to not be required so covering empty options is needed but other than that it should be the correct object i.e. datetime, date or time.

Thoughts? If you agree then this pull request should be good to go.

[mjparker777]

I am not sure what the labels mean? Does the "Needs further review" apply to me or someone else? Are we good on this?

[tomchristie]

You shouldn't need to handle the None case explicitly, as I believe that's handled as a catch all.

What's the behavior if you don't include this?

Is this behavior in order to catch empty strings and return None for them? (In which case I suspect this may be valid)

[mjparker777]

Hi Tom - If None is passed in then when it gets to this method it is an empty string ''.
With completed = serializers.DateTimeField(required=False) and completed is None you see this output:

2015-12-17 18:58:53,631 ERROR RequestDetailsHandler::get::371 
Traceback (most recent call last):
  File "/x/local/aitv2/automatic_integration_v2/eci/handlers/RequestDetailsHandler.py", line 368, in get
    return response.Response(RequestDetailsResponseSerializer(response_data).data,
  File "/Users/miparker/.virtualenvs/aitv3/lib/python2.7/site-packages/rest_framework/serializers.py", line 503, in data
    ret = super(Serializer, self).data
  File "/Users/miparker/.virtualenvs/aitv3/lib/python2.7/site-packages/rest_framework/serializers.py", line 239, in data
    self._data = self.to_representation(self.instance)
  File "/Users/miparker/.virtualenvs/aitv3/lib/python2.7/site-packages/rest_framework/serializers.py", line 472, in to_representation
    ret[field.field_name] = field.to_representation(attribute)
  File "/Users/miparker/.virtualenvs/aitv3/lib/python2.7/site-packages/rest_framework/serializers.py", line 614, in to_representation
    self.child.to_representation(item) for item in iterable
  File "/Users/miparker/.virtualenvs/aitv3/lib/python2.7/site-packages/rest_framework/serializers.py", line 472, in to_representation
    ret[field.field_name] = field.to_representation(attribute)
  File "/Users/miparker/.virtualenvs/aitv3/lib/python2.7/site-packages/rest_framework/serializers.py", line 472, in to_representation
    ret[field.field_name] = field.to_representation(attribute)
  File "/Users/miparker/.virtualenvs/aitv3/lib/python2.7/site-packages/rest_framework/fields.py", line 1071, in to_representation
    value = value.isoformat()
AttributeError: 'str' object has no attribute 'isoformat'

[tomchristie]

Minor point, but it'd be good if DateField mirrored these in layout too - i.e. move this https://github.com/tomchristie/django-rest-framework/pull/3731/files#diff-af402f515db75c7c6754453cf15455d9L1123 to the top of the method.

Otherwise I think this is looking good, tho just some clarification on exactly what those tests end up with if we don't include the fix would be helpful. Is it only the blank string case that is currently broken?

[mjparker777]

Hi Tom -
Modified datefield to match the other two.

If None is passed in then when it gets to this method (to_representation(self, value)) it (value) is an empty string ''.
With completed = serializers.DateTimeField(required=False) and completed is None you see this output:

2015-12-17 18:58:53,631 ERROR RequestDetailsHandler::get::371 
Traceback (most recent call last):
  File "/x/local/aitv2/automatic_integration_v2/eci/handlers/RequestDetailsHandler.py", line 368, in get
    return response.Response(RequestDetailsResponseSerializer(response_data).data,
  File "/Users/miparker/.virtualenvs/aitv3/lib/python2.7/site-packages/rest_framework/serializers.py", line 503, in data
    ret = super(Serializer, self).data
  File "/Users/miparker/.virtualenvs/aitv3/lib/python2.7/site-packages/rest_framework/serializers.py", line 239, in data
    self._data = self.to_representation(self.instance)
  File "/Users/miparker/.virtualenvs/aitv3/lib/python2.7/site-packages/rest_framework/serializers.py", line 472, in to_representation
    ret[field.field_name] = field.to_representation(attribute)
  File "/Users/miparker/.virtualenvs/aitv3/lib/python2.7/site-packages/rest_framework/serializers.py", line 614, in to_representation
    self.child.to_representation(item) for item in iterable
  File "/Users/miparker/.virtualenvs/aitv3/lib/python2.7/site-packages/rest_framework/serializers.py", line 472, in to_representation
    ret[field.field_name] = field.to_representation(attribute)
  File "/Users/miparker/.virtualenvs/aitv3/lib/python2.7/site-packages/rest_framework/serializers.py", line 472, in to_representation
    ret[field.field_name] = field.to_representation(attribute)
  File "/Users/miparker/.virtualenvs/aitv3/lib/python2.7/site-packages/rest_framework/fields.py", line 1071, in to_representation
    value = value.isoformat()
AttributeError: 'str' object has no attribute 'isoformat'