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post.scala

val IdArg = Argument("id", IntType)
val NameArg = Argument("name", StringType)

val Mutation = ObjectType("Mutation", fields[ShopRepository, Unit](
      Field("addCategory", CategoryType,
        arguments = IdArg :: NameArg :: Nil,
        resolve = c => c.ctx.addCategory(c.arg(IdArg), c.arg(NameArg))
      )
  ))