FindById in persistent

[Sudip Bhattarai]

I don't know if it's just a beginner problem, or insufficiency of the documentation, The getById is documented with following example.

personId <- insert $ Person "Michael" "Snoyman" 26
maybePerson <- get personId
case maybePerson of
Nothing -> liftIO $ putStrLn "Just kidding, not really there"
Just person -> liftIO $ print person


But  how do i do say  get person having id of 3?

maybePerson <- get 3  {- this doesn' twork with type mismatch-}
maybePerson <- get (PersonId 3)  {- this also doesn't work -}

[Sudip Bhattarai]

For schema below, How do I find a person by id 3?

share [mkPersist sqlSettings, mkMigrate "migrateAll"] [persistLowerCase|
Person
firstName String
lastName String
age Int Maybe
PersonName firstName lastName
deriving Show
|]

the Example provided in the persistent book says

personId <- insert $ Person "Michael" "Snoyman" 26
maybePerson <- get personId

But 
maybePerson <- get 3  will not compile.

[Michael Snoyman]

This section of the book gives a bit more information:

Persistent :: Yesod Web Framework Book- Version 1.6

You can use the toSqlKey function to help with this:

Database.Persist.Sql (stackage.org)

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[jsch...@gmail.com]

I just want to add some sentences because understanding this helped me once. Maybe it's already totally clear to you:

Often you don't need to convert from Int to PersonId.

For example in routes, you directly write

/persons/#PersonId

instead of

/persons/#Int

And if another entity points to a Person, than the type should also be PersonId instead of Int.