Add no-users option to DumpImporter and DumpExporter

[ranaldmiao]

At the moment, when exporting a contest using cmsDumpExporter, there is no option to omit information related to users during the export.
Thus, any user which is related to the contest (participants, admin, etc..) will also be included in the dump file. When importing this dump file into another CMS instance, cmsDumpImporter will attempt to create these users. If existing users with the same username exists, this will result in database IntegrityError, causing the import to fail.

This PR introduces the option to export a contest without any user information via cmsDumpExporter. (i.e. Just the tasks itself).

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This change is 

[codecov]

Codecov Report

Merging #1165 (f41a5d8) into master (91a32fc) will increase coverage by 0.13%.
The diff coverage is 90.32%.

@@            Coverage Diff             @@
##           master    #1165      +/-   ##
==========================================
+ Coverage   63.68%   63.82%   +0.13%     
==========================================
  Files         233      233              
  Lines       17113    17131      +18     
==========================================
+ Hits        10899    10934      +35     
+ Misses       6214     6197      -17     

Flag	Coverage Δ
functionaltests	47.62% <9.67%> (+<0.01%)	⬆️
unittests	44.14% <90.32%> (+0.04%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
cmscontrib/DumpImporter.py	69.90% <85.71%> (+0.38%)	⬆️
cmscontrib/DumpExporter.py	73.78% <92.85%> (+1.10%)	⬆️
cms/db/util.py	66.66% <100.00%> (+13.33%)	⬆️
cms/db/base.py	87.12% <0.00%> (-2.98%)	⬇️
cms/service/workerpool.py	66.11% <0.00%> (-2.23%)	⬇️
cms/service/esoperations.py	83.33% <0.00%> (-0.70%)	⬇️
cms/service/EvaluationService.py	74.62% <0.00%> (-0.50%)	⬇️
cms/grading/Job.py	89.28% <0.00%> (-0.45%)	⬇️
cms/io/service.py	71.51% <0.00%> (ø)
cms/db/filecacher.py	79.20% <0.00%> (ø)
... and 6 more

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[andreyv]

Thanks.

Observe that this feature is conceptually very similar to a contest loader: there is some task data and one wants to import it. Just for clarification, do you use it for a similar purpose, e.g., prepare a contest on a staging server and import it on a testing/production server?

[ranaldmiao]

Yes, this is for the purpose you mentioned. The 'staging' server as well as the testing/production server are both CMS.

At the moment, this is done by exporting the contest (using cmsDumpExporter) from the staging CMS instance and then re-importing them into the production instance using cmsDumpImporter.

Would you recommend looking into implementing a ContestLoader that reads from a cms dump exporter format?

[andreyv]

Thanks for the explanation.

I think the "recommended" and more robust solution would be to prepare the contest using one of the loader formats in the first place, and import it both on the staging and production servers.

But I suppose a complementary solution like this one can be added as well, if it is useful. In this case, you should also add the same option to DumpImporter.py to keep it synchronized with DumpExporter.py.

[ranaldmiao]

@andreyv Requested changes have been made, do review when you have the time.

Thanks once again :)

[andreyv]

Thanks, it looks good now.

I see that you added tests and also fixed a bug that could cause DumpImporter to import everything instead of skipping items as requested — nice!

I added some minor changes in f41a5d8:

• In DumpExporter, simplify the user-related class list and only check classes that can be reached from root (from Contest and Task classes). The other previously listed classes, including User, should not appear there.
• In DumpImporter, also skip Announcement. Otherwise it could indirectly import Admins as well when importing a full dump with -X.
• Whitespace and indentation fixes.

I'll merge this MR in a few days if you have no further comments.

[andreyv]

Merged!