Issues with Date JSON Serialization

[JohnOmernik]

I am having an issue where Python reports a circular reference.

I believe the the issue comes up here:

def json_iso_dttm_ser(obj):
"""
json serializer that deals with dates
>>> dttm = datetime(1970, 1, 1)
>>> json.dumps({'dttm': dttm}, default=json_iso_dttm_ser)
'{"dttm": "1970-01-01T00:00:00"}'
"""
if isinstance(obj, datetime):
obj = obj.isoformat()
return obj

(in utils.py)

Based on http://stackoverflow.com/questions/14249115/serializing-output-to-json-valueerror-circular-reference-detected

My data I am querying my data source directly (this is the exact query that caravel is trying to run) I get these results:

trans_day is selected as a dttm column... I am just confused at why this cirucular reference is coming up...

+-------------+--------+
| trans_day | cnt |
+-------------+--------+
| 2015-06-02 | 13265 |
| 2015-01-06 | 13031 |
| 2015-05-19 | 12875 |
| 2015-06-16 | 12746 |
| 2015-05-28 | 12724 |
| 2015-05-26 | 12692 |
| 2015-04-21 | 12617 |
| 2015-06-03 | 12410 |
| 2015-05-05 | 12317 |
| 2015-04-07 | 12308 |
+-------------+--------+

The full stack trace is:

Traceback (most recent call last):
File "/usr/local/lib/python2.7/dist-packages/flask/app.py", line 1836, in call
return self.wsgi_app(environ, start_response)
File "/usr/local/lib/python2.7/dist-packages/flask/app.py", line 1820, in wsgi_app
response = self.make_response(self.handle_exception(e))
File "/usr/local/lib/python2.7/dist-packages/flask/app.py", line 1403, in handle_exception
reraise(exc_type, exc_value, tb)
File "/usr/local/lib/python2.7/dist-packages/flask/app.py", line 1817, in wsgi_app
response = self.full_dispatch_request()
File "/usr/local/lib/python2.7/dist-packages/flask/app.py", line 1477, in full_dispatch_request
rv = self.handle_user_exception(e)
File "/usr/local/lib/python2.7/dist-packages/flask/app.py", line 1381, in handle_user_exception
reraise(exc_type, exc_value, tb)
File "/usr/local/lib/python2.7/dist-packages/flask/app.py", line 1475, in full_dispatch_request
rv = self.dispatch_request()
File "/usr/local/lib/python2.7/dist-packages/flask/app.py", line 1461, in dispatch_request
return self.view_functionsrule.endpoint
File "/usr/local/lib/python2.7/dist-packages/flask_appbuilder/security/decorators.py", line 26, in wraps
return f(self, _args, *_kwargs)
File "/usr/local/lib/python2.7/dist-packages/caravel/models.py", line 1294, in wrapper
return f(_args, *_kwargs)
File "/usr/local/lib/python2.7/dist-packages/caravel/views.py", line 557, in explore
payload = obj.get_json()
File "/usr/local/lib/python2.7/dist-packages/caravel/viz.py", line 269, in get_json
return self.json_dumps(payload)
File "/usr/local/lib/python2.7/dist-packages/caravel/viz.py", line 375, in json_dumps
return json.dumps(obj, default=utils.json_iso_dttm_ser)
File "/usr/lib/python2.7/json/init.py", line 251, in dumps
sort_keys=sort_keys, **kw).encode(obj)
File "/usr/lib/python2.7/json/encoder.py", line 207, in encode
chunks = self.iterencode(o, _one_shot=True)
File "/usr/lib/python2.7/json/encoder.py", line 270, in iterencode
return _iterencode(o, 0)
ValueError: Circular reference detected

[JohnOmernik]

So it doesn't seem to matter whether the grouped column (trans_day) is marked as dttm column. It has the same error no matter what. So It must be auto detected the YYYY-MM-DD format and trying to do something with it?

[xrmx]

Same here with 0.9.0, i got this on a new project when opening the page to create a new slice (http://127.0.0.1:8088/caravel/explore/table/3/)

I've added this to help debugging:

diff --git a/caravel/utils.py b/caravel/utils.py
index 7e3d4c0..f117576 100644
--- a/caravel/utils.py
+++ b/caravel/utils.py
@@ -221,6 +221,10 @@ def json_iso_dttm_ser(obj):
     """
     if isinstance(obj, datetime):
         obj = obj.isoformat()
+    else:
+        raise TypeError(
+             "Unserializable object {} of type {}".format(obj, type(obj))
+        )
     return obj

It explodes with this:

TypeError: Unserializable object 0 of type <class 'numpy.int64'>

This how my data is structured:

    ('metrica', 'TEXT'),
    ('disciplina', 'TEXT'),
    ('opera', 'TEXT'),
    ('casa_editrice', 'TEXT'),
    ('tipologia', 'TEXT'),
    ('data', 'DATE'),
    ('scuola', 'TEXT'),
    ('tipologia_utente', 'TEXT'),
    ('provincia', 'TEXT'),
    ('nazione', 'TEXT')