Alternative representation of Entity

[tchoutri]

At present time, Entity is a typeclass and we pass the dictionary implicitly to the functions.

It is suggested by @dminuoso that it could be a record with a phantom type:

type role Entity nominal

data Entity (a :: Type) = Entity
  { tableName :: Text
  , primaryKey :: Field
  , fields :: Vector Field
  , schema :: Maybe Text
  }

Question coming from a remark of @kozross:
Can we do more to avoid sneaky/accidental retagging?
Like Entity User -> Entity Group for instance?

The constructor should not be exposed otherwise this is going to end badly.

Discussion is open.

[tchoutri]

Personally I'm tempted to take this approach:

type role Entity nominal

-- | The constructor is not exported
data Entity (a :: Type) = Entity
  { _tableName :: String
  , _primaryKey :: String
  , _schema :: Maybe String
  , _fields :: [String]
  }
  deriving stock (Eq, Show)

entity :: String
       -> String
       -> Maybe String
       -> [String]
       -> Entity a
entity = Entity

instance HasField "tableName" (Entity r) String where
    getField e = e._tableName

instance HasField "primaryKey" (Entity r) String where
    getField e = e._primaryKey

instance HasField "schema" (Entity r) (Maybe String) where
    getField e = e._schema

instance HasField "fields" (Entity r) [String] where
    getField e = e._fields