Comment by tomhoule | Hacker News Reader

Comment by tomhoule | Hacker News Reader

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(prisma migrate team member here)

The development flow in migrate (the `migrate dev`) command is quite pedantic: it will check things like migrations missing from your migrations folder but already applied to the dev database, or migrations that were modified since they were applied (via a checksum) and guide you towards resolving the problem. That can happen because of merges, but even more commonly when you are just switching branches locally, or editing migrations.

We're also looking into ways to integrate with your CI and review process to provide more insight, for example when your branch gets stale and you need to "rebase" your migrations on the migrations from the main branch. It's something we are actively exploring, and we're more than happy to get your feedback and ideas on github/slack :)

My personal view is that _some level_ of consciousness of the migration process (schema and data) will always be required from developers on large enough projects. What we can do is build tools that help people getting their migrations right, but it can't be completely automated. There's a lot more to do, now that we have a stable, production ready foundation.

Thank you for your clarification.

I like to think about a single migration being a function and a migration history multiple functions being composed.

Category theory's main subject (I think) is composition and a lot of good ideas can be taken from there (see this paper: "Functorial Data Migration"[1]).

There is an obvious relationship between a schema and the data, and a migration operates on both. The schema might be versioned, but unless you use a Schema-less database (ie: MongoDB) and handle the data versioning application side, your data is not.

Any document/graph-based database can avoid this problem by assigning a version to your documents (like apiVersion+kind in Kubernetes), then the application should know how to process each version of the data.

In an SQL database, it would require different tables which complexify the data model.

IMHO, in every case, you need to handle some of the logic application side or maintain an history of your data (bye-bye storage space?).

[1] - http://math.mit.edu/~dspivak/informatics/CD-FDM.pdf

Ooh it's interesting you mention David Spivak's work, I got interested into it recently. Some of these ideas are being commercialized by https://conexus.com/ (he's a co-founder). You might also be interested by Project Cambria[1] for novel ideas about data and schema migrations based on lenses.

We haven't gone in the fancy direction yet, because we wanted to first have the tool our users told us they were missing - namely a migration tool similar to what other ORMs have, but playing on the strengths of the Prisma schema. But these novel ideas about migrations are definitely something we always read with a lot of interest and love to discuss — I hope we get to implement something radical like that some day.

[1]: https://www.inkandswitch.com/cambria.html

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