8000 primary_key mismatch with sum in MySQL · Issue #24 · flyerhzm/eager_group · GitHub
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primary_key mismatch with sum in MySQL #24

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maxigs opened this issue Dec 29, 2021 · 2 comments
Open

primary_key mismatch with sum in MySQL #24

maxigs opened this issue Dec 29, 2021 · 2 comments

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@maxigs
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maxigs commented Dec 29, 2021

I found a issue with MySQL (or MariaDB in my case) and using sum aggregation.

The Primary keys on the DB query seem to be returned with string primary_keys. Which then does not match the primary_key of the given record for mapping the values.

As the tests only run against sqlite this issue does not seem present. But i thought it might be interesting for someone else.

My change can be seen here: https://github.com/maxigs/eager_group/blob/master/lib/eager_group/preloader.rb#L48
(I just copied the whole class into an initializer in my rails project for now, so i could test it with real database)
@flyerhzm
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@maxigs hmmm...I didn't face such issue.
This change will break if someone use uuid as primary key

@maxigs
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maxigs commented Dec 31, 2021

@flyerhzm

You are corret. I know it's not a real fix, that's why i did not create a pull-request, but still found it might be usefull for someone else facing a similar issue.

I spent a couple hours debugging, why some numbers did not add up, until i fould thataggregate_hash was returning a hash with string-keys, for a model where primary-keys are integers. So every sum was retuning zero values.
It only happend with sum not any other method. Also it only happend in a real application using MariaDB, not with the tests in the gem itself (using SQLite).
Might rather be a issue in Activerecord or even Mysql driver, not sure - unfortunately i did not have more time to dig even deeper so far.

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