error: could not find implicit value for parameter DS: fetch.DataSource[UserId, A]

[mikoSL]

Hello,

when I tried to run the code
def getUser(id: UserId): Fetch[User] = Fetch(id) // or, more explicitly: Fetch(id)(UserSource)

It showed error: error: could not find implicit value for parameter DS: fetch.DataSource[UserId, A].

I have tried another example from Fetch github
`implicit object ToStringSource extends DataSource[Int, String]{
override def name = "ToString"

override def fetchOne(id: Int): Query[Option[String]] = {
Query.sync({
println(s"[${Thread.currentThread.getId}] One ToString $id")
Option(id.toString)
})
}
override def fetchMany(ids: NonEmptyList[Int]): Query[Map[Int, String]] = {
Query.sync({
println(s"[${Thread.currentThread.getId}] Many ToString $ids")
ids.toList.map(i => (i, i.toString)).toMap
})
}
}

def fetchString(n: Int): Fetch[String] = Fetch(n) // or, more explicitly: Fetch(n)(ToStringSource)`

It had the same error. Errors: could not find implicit value for parameter DS: fetch.DAtaSource[Int, A].

Fetch is a very nice tool, I really want to learn how to use it, but I am stuck here.
I can not find any similar question from google.
Can you please help?