MongoDB: Error while using translate ValueError: max() iterable argument is empty

[amotl]

@delusion8399 added a report at crate/mongodb-cratedb-migration-tool#25. Because we are archiving that repository, we are adding the report here instead.

Hi, getting this error while using translate

    type = max(types, key=lambda item: types[item]["count"])
ValueError: max() arg is an empty sequence

[amotl]

Dear @delusion8399,

in order to approach that problem, maybe you can share your collection schema with us, and a few samples worth of data? We would love to add corresponding improvements to make the program more robust.

With kind regards,
Andreas.

[amotl]

Silly Reproduction

I have been able to reproduce the problem on a narrow scope:

$ python3.10

>>> types = {}
>>> max(types, key=lambda item: types[item]["count"])
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: max() arg is an empty sequence

Thoughts

I guess your collection may use a MongoDB data type the program does not know about, trips on it, and fails to convey that flaw in a good way. If you could tell us about all data types used within the collection at hand, it could already give us more hints to investigate more closely. Thanks!

[amotl]

Dear @delusion8399,

that patch improved quite a few edge case situations in the MongoDB table loader.

• MongoDB: Various fixes and improvements #216

Maybe you would like to give it another try after upgrading to the most recent version of cratedb-toolkit?

With kind regards,
Andreas.

[amotl]

I've just been able to spot this shape of schema information on real-world data, which seems to trip that very error. So, I may assume a fix is neigh.

"items": {
    "count": 1,
    "types": {
        "ARRAY": {
            "count": 1,
            "types": {}
        }
    }
}

Most probably, it is about empty arrays/lists, where naturally an inner type can't be derived from.

[delusion8399]

Thank you so much for taking this so seriously.
I was able to do that manually using CSV dump.

Anyways If In future I got such case I would definitely use and contribute to this tool.