Time Series Table: group-by keys must be strings

[rumbin]

Make sure these boxes are checked before submitting your issue - thank you!

• I have checked the superset logs for python stacktraces and included it here as text if any
• I have reproduced the issue with at least the latest released version of superset
• I have checked the issue tracker for the same issue and I haven't found one similar

Superset version

0.20.3

Expected results

Any groupable column or combination of columns can be used to group by, when creating a Time Series Table slice

Actual results

Rendering the slice fails if…

• …more than one groupable column is selected; error: 'keys must be a string'
• …only one column is selected for grouping but the column is of type int instead of str

Steps to reproduce

…self explanatory, I suppose…

[scott-retair]

I met the same issue

[SpyderRivera]

If you are grouping by an int, is it really an int? Or is it an id that can be cast as a string?

[mistercrunch]

Could not reproduce on master can you confirm?

[tvorogme]

Same issue

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.