Slick/Scala: What is a Rep[Bind] and how do I turn it into a value?

Question

I'm trying to figure out Slick (the Scala functional relational model). I've started to build a prototype in Slick 3.0.0 but of course... most of the documentation is either out of date or incomplete.

I've managed to get to a point where I can create a schema and return an object from the database.

The problem is, what I'm getting back is a "Rep[Bind]" and not the object I would expect to get back. I can't figure out what to do this this value. For instance, if I try something like rep.countDistinct.result, I get a crash.

Here's a quick synopsis of the code... some removed for brevity:

class UserModel(tag: Tag) extends Table[User](tag, "app_dat_user_t") {
    def id = column[Long]("n_user_id", O.PrimaryKey)
    def created = column[Long]("d_timestamp_created")

    def * = (id.?, created) <> (User.tupled, User.unapply)
}

case class User(id: Option[Long], created: Long)

val users = TableQuery[UserModel]

(users.schema).create

db.run(users += User(Option(1), 2))

println("ID is ... " + users.map(_.id)) // prints "Rep[Bind]"... huh?

val users = for (user <- users) yield user

println(users.map(_.id).toString) // Also prints "Rep[Bind]"...

I can't find a way to "unwrap" the Rep object and I can't find any clear explanation of what it is or how to use it.

Just a little more info: Most of the documentation I've found suggestions that I could do something like "users.foreach(println)" but, users.foreach is undefined. — Zaphod, May 08 '15 at 21:00

score 12 · Accepted Answer · edited Dec 29 '17 at 16:17

Rep[] is a replacement to the Column[] datatype used in slick .

users.map(_.id) returns values of the Column('n_user_id') for all rows

val result : Rep[Long] = users.map(_.id)

users.map(_.id) // => select n_user_id from app_dat_user_t;

The obtained value is of type Column[Long] [ which is now Rep[Long] ]. You cannot directly print values of the above resultSet as it is not of any scala collection type

You can first convert it to some scala collection and then print it as below :
```
var idList : List[Long] = List()
users.map(_.id).forEach(id =>
idList = idList :+ id
)
```
println(idList)** // if you need to print all ids at once

else you can simply use :

users.map(_.id).forEach(id =>
println(id)
) // print for each id

And ,

val users = TableQuery[UserModel] // => returns Query[UserModel, UserModel#TableElementType, Seq])

val users = for (user <- users) yield user // => returns Query[UserModel, UserModel#TableElementType, Seq])

both mean the same , So you can directly use the former and remove the latter

Slick/Scala: What is a Rep[Bind] and how do I turn it into a value?

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