Importing chart over API fails if the chart was built on top of a virtual dataset

[krsnik93]

Importing chart over API fails if the chart was built on top of a virtual dataset. I exported the chart with the /chart/export endpoint and then tried POSTing the resulting .zip to /chart/import.

Expected results

Expect chart to get uploaded successfully.

Actual results

Feb 19 15:17:45 superset gunicorn[10599]:   File "/usr/local/lib/python3.8/site-packages/superset/models/slice.py", line 103, in cls_model
Feb 19 15:17:45 superset gunicorn[10599]:     return ConnectorRegistry.sources[self.datasource_type]
Feb 19 15:17:45 superset gunicorn[10599]: KeyError: 'view'
Feb 19 15:17:45 superset gunicorn[10599]: During handling of the above exception, another exception occurred:
Feb 19 15:17:45 superset gunicorn[10599]: Traceback (most recent call last):
Feb 19 15:17:45 superset gunicorn[10599]:   File "/usr/local/lib/python3.8/site-packages/superset/charts/api.py", line 993, in import_
Feb 19 15:17:45 superset gunicorn[10599]:     command.run()
Feb 19 15:17:45 superset gunicorn[10599]:   File "/usr/local/lib/python3.8/site-packages/superset/charts/commands/importers/dispatcher.py", line 66, in run
Feb 19 15:17:45 superset gunicorn[10599]:     raise exc
Feb 19 15:17:45 superset gunicorn[10599]:   File "/usr/local/lib/python3.8/site-packages/superset/charts/commands/importers/dispatcher.py", line 55, in run
Feb 19 15:17:45 superset gunicorn[10599]:     command.run()
Feb 19 15:17:45 superset gunicorn[10599]:   File "/usr/local/lib/python3.8/site-packages/superset/commands/importers/v1/__init__.py", line 71, in run
Feb 19 15:17:45 superset gunicorn[10599]:     raise self.import_error()
Feb 19 15:17:45 superset gunicorn[10599]: superset.charts.commands.exceptions.ChartImportError: Import chart failed for an unknown reason

How to reproduce the bug

1. Create a virtual dataset in SQL Lab
2. Create a chart on top of that dataset
3. Export chart via REST API /chart/export endpoint with:
   curl -v --cookie "session=<your_cookie>" --output <filename>.zip http://<your_host>/api/v1/chart/export/?q=[<your_chart_id>]
4. Try to import resulting .zip file with:
   curl 'http://<your_host>/api/v1/chart/import/' \ -X POST \ -H 'Cookie: session=<your_cookie>' \ -H "X-CSRF-Token: <your_csrf_token>" \ -F formData=@<filename>.zip \ -F overwrite=true \ --compressed \ --insecure

Environment

(please complete the following information):

• superset version: 1.0.0
• python version: 3.8.7
• node.js version: v12.20.1

Checklist

Make sure to follow these steps before submitting your issue - thank you!

• I have checked the superset logs for python stacktraces and included it here as text if there are 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.

[junlincc]

@dpgaspar could you please take a look? thanks Daniel!

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