How to use nextval with a newtyped ID? #172
Description
I have the following table:
newtype UserId = UserId { toInt32 :: Int32 }
deriving newtype (DBEq, DBType, Eq, Show)
deriving newtype instance DBType (PasswordHash a)
data User f = User
{ userId :: Column f UserId,
userName :: Column f Text,
userPassword :: Column f (PasswordHash Bcrypt)
}
deriving stock (Generic)
deriving anyclass (Rel8able)
And I'm trying to figure out how to insert a user. I have this snippet in a Yesod Handler
hashed <- liftIO <| hashPassword <| mkPassword password
let user = User {
userId = nextval "user_id_seq",
userName = lit username,
userPassword = lit hashed
}
Yesoder conn <- getYesod
liftIO $ run (insertUser user) conn
pure "registered"
But I'm getting
• Couldn't match type ‘GHC.Int.Int64’ with ‘UserId’
Expected: Column Expr UserId
Actual: Expr GHC.Int.Int64
• In the ‘userId’ field of a record
In the expression:
User
{userId = nextval "user_id_seq", userName = lit username,
userPassword = lit hashed}
In an equation for ‘user’:
user
= User
{userId = nextval "user_id_seq", userName = lit username,
userPassword = lit hashed}
|
87 | userId = nextval "user_id_seq",
| ^^^^^^^^^^^^^^^^^^^^^
I thought I might be able to do something like UserId <$> nextval "user_id_seq" to obtain an Expr UserId, but Expr doesn't have a Functor instance. I only have the fuzziest understanding of how expr works, so I assume there's some good reason for this. On reflection this probably doesn't make sense.
How do I handle this correctly? It seems like a pretty foundational use case.