> This isn't really vendor lock-in, though. It's simply a technical/design lock-in. Going from unstructured to structured data presents problems, and if you do that, it's rightfully up to you to fix.
This is true, but it's also kind of vendor lock-in because there's a whole query language and aggregation pipeline for Mongo that's completely different to other databases. If I was using an RDBMS and was switching from MySQL to Postgres I think I would likely have a much easier time, because fundamentally it's all SQL (I know, there are differences between Postgres and MySQL, but it's a lot less, and a good ORM will smooth some of it out for you - at least initially)
I think this is basically equivalent to your example of not being able to easily move from AWS to Google Cloud because of their different APIs.
This is true, but it's also kind of vendor lock-in because there's a whole query language and aggregation pipeline for Mongo that's completely different to other databases. If I was using an RDBMS and was switching from MySQL to Postgres I think I would likely have a much easier time, because fundamentally it's all SQL (I know, there are differences between Postgres and MySQL, but it's a lot less, and a good ORM will smooth some of it out for you - at least initially)
I think this is basically equivalent to your example of not being able to easily move from AWS to Google Cloud because of their different APIs.
It doesn't seem like SQL-to-Mongo is impossible to implement, because there is third-party tooling for that (which I haven't tried): https://studio3t.com/knowledge-base/articles/sql-query/