Why does compilation fail with "not found: value Users"? - postgresql

Question

I want to retrieve a row from my default database postgres. I have table "Users" defined already.
conf/application.conf
db.default.driver=org.postgresql.Driver
db.default.url="jdbc:postgresql://localhost:5234/postgres"
db.default.user="postgres"
db.default.password=""
controllers/Application.scala
package controllers
import models.{UsersDatabase, Users}
import play.api.mvc._
object Application extends Controller {
def index = Action {
Ok(views.html.index(UsersDatabase.getAll))
}
}
models/Users.scala
package models
import java.sql.Date
import play.api.Play.current
import play.api.db.DB
import slick.driver.PostgresDriver.simple._
case class User(
id: Int,
username: String,
password: String,
full_name: String,
email: String,
gender: String,
dob: Date,
joined_date: Date
)
class Users(tag: Tag) extends Table[User](tag, "Users") {
def id = column[Int]("id")
def username = column[String]("username", O.PrimaryKey)
def password = column[String]("password")
def full_name = column[String]("full_name")
def email = column[String]("email")
def gender = column[String]("gender")
def dob = column[Date]("dob")
def joined_date = column[Date]("joined_date")
def * = (id, username, password, full_name, email, gender, dob, joined_date) <> (User.tupled, User.unapply)
}
object UsersDatabase {
def getAll: List[User] = {
Database.forDataSource(DB.getDataSource()) withSession {
Query(Users).list
}
}
}
While accessing http://localhost:9000/ it gives compilation error:
[error] .../app/models/Users.scala:36: not found: value Users
[error] Query(Users).list
[error] ^
[error] one error found
[error] (compile:compile) Compilation failed
How to resolve this error and access data properly?

Answer 1

The compilation error message says it all - there's no value Users to use in the scope.
Change the object UsersDatabase to look as follows:
object UsersDatabase {
val users = TableQuery[Users]
def getAll: List[User] = {
Database.forDataSource(DB.getDataSource()) withSession { implicit session =>
users.list
}
}
}
And the error goes away since you're using the local val users to list users in the database.
As described in Querying in the official documentation of Slick session val is an implicit value of list (as final def list(implicit session: SessionDef): List[R]), and hence implicit session in the block:
All methods that execute a query take an implicit Session value. Of
course, you can also pass a session explicitly if you prefer:
val l = q.list(session)