My Yesod Model

User
    ident Text
    password Text Maybe
    UniqueUser ident
    deriving Typeable
Email
    email Text
    userId UserId Maybe
    verkey Text Maybe
    UniqueEmail email
Comment json -- Adding "json" causes ToJSON and FromJSON instances to be derived.
    message Text
    userId UserId Maybe
    deriving Eq
    deriving Show

 -- By default this file is used in Model.hs (which is imported by Foundation.hs)