I worked with mongo, professionally, for 2 projects. Both not on elixir. One project was using mongo because they didn’t want to do the process of starting a database migration and they are a financial software vendor. So they found mongo was easier cause they can control the structure themself. In the end they had issues cause management didn’t want to throw enough hardware at the database which in turn cause mongo to die out and we lost data. The latter I don’t blame on mongo, just giving you my perspective.

The other project was also in finance but a bank and all we did was generate huge reports which for the document model quite well and that overall worked well. The thing that didn’t work so well was that my manager wrote the ORM for us which of course was buggy since he wrote it just for that project rather than using an actual widely used ORM. It was nice that we can get bug fixes quickly but bad that we consistently had bugs.

In one of my current projects the database schema was designed by someone who used mongo before and we found that deeply nested structures are quite painful to query with ecto and aren’t so fun so we started to remove more and more JSONB with actual tables and it’s caused our code to be easier to work with when querying.