Reduce of empty array with no initial value

[Nalum]

Running the following on MongoDB 3.0.8 worked (I think I may have also been using an older version of the shell command): mongo --host localhost --eval "var collection = 'events', query = {'title': 'event title'};" database variety.js

The collection I'm querying has over 15 million documents in it. At the time that it worked it had between 12 and 13 million documents. If I run the query on the database and get a count there are ~350 documents.

We have recently upgraded to MongoDB 3.0.9 and running the same command gives the below output:

MongoDB shell version: 3.2.1
connecting to: localhost:27017/database
Variety: A MongoDB Schema Analyzer
Version 1.5.0, released 14 May 2015
Cannot use 'commands' readMode, degrading to 'legacy' mode
Using collection of "events"
Using query of { "title" : "event title" }
Using limit of 0
Using maxDepth of 99
Using sort of { "_id" : -1 }
Using outputFormat of "ascii"
Using persistResults of false
Using resultsDatabase of "varietyResults"
Using resultsCollection of "eventsKeys"
Using resultsUser of null
Using resultsPass of null
Using plugins of [ ]
2016-02-08T21:29:05.740+0000 E QUERY    [thread1] TypeError: reduce of empty array with no initial value :
createAsciiTable@variety.js:333:19
@variety.js:365:10
@variety.js:12:2

failed to load: variety.js

If there is anything else I can provide let me know.

[todvora]

Hi Luke,
Thank you for your bugreport! I'll try to replicate and fix this issue.

Everyone: maybe it's time to integrate some Docker magic, to be able to test on several different MongoDB versions...

Regards,
Tomas

[JamesCropcho]

Tomáš,

Now that we've got this Docker stuff mostly figured out, are you able to reproduce Luke's issue or not so much?

James

[todvora]

Hi James,
Unfortunately not, not with the current test suite. I am still looking for the cause of this issue.

Regards,
Tomas

[JamesCropcho]

Luke,

Please pardon—we don't seem able to reproduce. Are you still experience this issue? Any insight it weirdness of this collection which might cause an usual error? Or if not, that's fine, too; just trying to sleuth it out (ha).

James

[todvora]

Hi Luke,
It could be really helpful, if you could provide some minimized / anonymized collection to run tests against. Would it be possible?

It seems, that variety tries to print into the ascii table a row, which does not contain any values. But where is it come from... I could probably fix the consequence. But without knowing the original cause, it will bite us somewhere else next time.

Thanks,
Tomas

[Nalum]

@todvora @JamesCropcho I'll try get a sample of data to you over the weekend. I'm gonna run it again myself and see how it goes. It is possible that some of the new data cased the issue.

[JamesCropcho]

Luke and Tomáš, I'm going to close this ticket/issue for now. By all means please feel free to re-open when we get more information or insights. Hope you two are having a nice week. —James

[hdavidzhu]

Repro'ed. This happens when the query causes the db to not return any values. When the resulting array is empty [], we get this error.

[JamesCropcho]

Thank you for letting us know, David ( @hdavidzhu ). Wow, this sounds like it's likely quite a commonly encountered bug, and it's been around for two years! (Hence, our appreciation, once again.) I have re-opened the issue for consideration.

@todvora It's surprising that the test suite wouldn't catch this, at least if indeed happens any time the initial query to the target collection doesn't return values. What do you think?