elephants VS hasql-th

💡 Remember that you can see the complete code in the repo.

💡 If you want to follow allow at home, the repository contains all the imports and data types — we omit most of them from the tutorial for simplicity.

All the other tables look quite similar; see the repo for the rest of the boilerplate. One interesting bit is foreign keys / referencing other primary keys; for example, product_id and category_id in the mapping table look like are defined as PrimaryKey ProductT f (not Columnar f Int64):

See the repo for the rest of the boilerplate.

Hasql is an ecosystem of libraries. To keep it simple, let’s limit ourselves to core hasql, hasql-transaction, and hasql-th. We’re using hasql 1.6.3.2 published in 2023.

unexpected '&'

https://github.com/nikita-volkov/hasql-th#error-example-1

There is also a Haskell port of the original PostgreSQL parser, implemented using megaparsec, which makes it highly flexible and hackable: https://github.com/nikita-volkov/hasql-th#implementation

I'd consider hasql-th a good example in what concerns databases. Otherwise, I just use aeson together with deriving-aeson and lens-aeson.