DiazCarrete: "Trying to learn persistent/esq…" - Hachyderm.io

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DiazCarrete @DiazCarrete@hachyderm.io

Trying to learn persistent/esqueleto

https://www.yesodweb.com/book/persistent

https://hackage.haskell.org/package/persistent
persistent-postgresql https://hackage.haskell.org/package/persistent-postgresql
the Persistent entity syntax https://hackage.haskell.org/package/persistent-2.14.6.3/docs/Database-Persist-Quasi.html
esqueleto https://hackage.haskell.org/package/esqueleto

Screen capture from the Yesod book.

However, there is one issue that newcomers are often bothered by: why are IDs and values completely separate? It seems like it would be very logical to embed the ID inside the value. In other words, instead of having:

data Person = Person { name :: String }
have

data Person = Person { personId :: PersonId, name :: String }

Well, there’s one problem with this right off the bat: how do we do an insert? If a Person needs to have an ID, and we get the ID by inserting, and an insert needs a Person, we have an impossible loop. We could solve this with undefined, but that’s just asking for trouble.

"One last trick you can do with attributes is to specify the names to be used for the SQL tables and columns. This can be convenient when interacting with existing databases."

Jan 11, 2025, 04:41 PM··Web

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