CODEWITHSUNDEEP
postgresqlhaskellderivingpostgresql-simple
Razumov
Razumov

Reputation: 324

Deriving FromRow on a type with [String] field

I am building a haskell server with a postgres database. I am using postgresql-simple to query the db.

I have the following type:

data Reading = Reading
  { id :: UUID
  , title :: String
  , authors :: [String]
  , startDate :: Day
  , finishDate :: Maybe Day
  }
  deriving (Eq, Show, Generic, FromRow)

This results in the following compiler error:

No instance for (Database.PostgreSQL.Simple.FromField.FromField
                        [String])
       arising from a use of ‘Database.PostgreSQL.Simple.FromRow.$dmfromRow’

In the documentation, I do not see an instance defined for [String]. It seems like one should exist. Is there one I can use or should I be thinking about defining my own?

Edit:

I can define

instance FromRow Reading where
  fromRow =
    Reading
      <$> field
      <*> field
      <*> (fromPGArray <$> field)
      <*> field
      <*> field

But this goes into cumbersome territory.

Upvotes: 0

Views: 68

Answers (0)

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