Is it possible to treat a primary key as an Int64? about esqueleto HOT 1 CLOSED

-- Must use this qualified lookup, else will get:
--     * Couldn't match type ‘BaseBackend backend’ with ‘SqlBackend'
import qualified Database.Esqueleto.Internal.Sql as EIS

-- ...

    E.case_
        [ E.when_ (p E.^. ProductKind E.==. (E.val $ BookProductType))
            -- Force Haskell to accept the underlying value as the required return Value.
            -- Not very safe, but at least the function clearly indicates that.
            E.then_ $ EIS.veryUnsafeCoerceSqlExprValue $ mBook E.?. BookProductId
        ]
        (E.else_ E.nothing)

-- ...