Accessing postgres using slick is not working - postgresql

Question

I have following environment scala2.11.8 / akka 2.4.8 / slick 3.1.1 / postgreSQL 9.6
I have done following configuration in application.conf
mydb {
driver = "slick.driver.PostgresDriver$"
db {
url = "jdbc:postgresql://localhost:5432/mydb"
driver = org.postgresql.Driver
user="postgres"
password="postgres"
numThreads = 10
connectionPool = disabled
keepAliveConnection = true
}
}
The DB access is done in class
package mib
import slick.driver.PostgresDriver.api._
import scala.concurrent.ExecutionContext.Implicits.global
class DBAccess {
import scala.concurrent.Future
import scala.concurrent._
import scala.concurrent.duration._
import slick.backend.DatabaseConfig
import slick.driver.JdbcProfile
import slick.driver.PostgresDriver
import slick.driver.PostgresDriver.api._
import slick.jdbc.JdbcBackend.Database
println("creating database")
val dbConfig: DatabaseConfig[PostgresDriver] = DatabaseConfig.forConfig("mydb")
val db = dbConfig.db
try{
val accesspoints = TableQuery[mibPoint]
// SELECT * FROM users WHERE username='john'
val q = for (a <- accesspoints) yield a.mib_id
val dbAction = q.result
val f: Future[Seq[String]] = db.run(dbAction)
Await.result(f, Duration.Inf)
f.onSuccess { case s => println(s"Result: $s") }
}
catch
{
case _: Throwable =>println("got some exception")
}
finally
db.close
}
// this is a class that represents the table I've created in the database
class mibPoint(tag: Tag) extends Table[(String, Double,Double)](tag, "mib_non_info") {
def mac_id = column[String]("mib_id",O.PrimaryKey)
def lat = column[Double]("lat")
def lng = column[Double]("lng")
def * = (mib_id, lat,lng)
}
This class is called from APP object as
object wmib extends App {
val mWBootStrapper = new bootStrap
mWBootStrapper.ReadProperties();
val mdB = new DBAccess
}
However after running, I always get the output as "got some exception"
I have tried to enable logging using slf4j/logback but still i do not see much in the logs.
The above seems like very trivial and probably i am missing something obvious.
Thanks in advance,
Vishal
I added the exception handling as suggested by sarvesh. That was cool and thank you.
However my problem vanished and there was no exception.
What happened?
Earlier in the day, I had attempted to access the DB using the java JDBC way.
i.e. just to check that there is nothing wrong with DB and DB access.
In the process, I downloaded and added the postgresDriver in the classpath. Earlier that was not the case.
Since the driver was now in the path, the code just worked.
Since I was not printing the exception, i was not realizing the error.
I then removed the driver jar AND i got the following error.
01:44:08.224 [mydb.db-1] DEBUG slick.jdbc.JdbcBackend.statement - Preparing statement: select "mib_id" from "mibpoint"
01:44:08.224 [mydb.db-1] DEBUG slick.jdbc.DriverDataSource - Driver org.postgresql.Driver not already registered; trying to load it
java.lang.ClassNotFoundException: org.postgresql.Driver
at java.lang.ClassLoader.findClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at slick.util.ClassLoaderUtil$$anon$1.loadClass(ClassLoaderUtil.scala:12)
at slick.jdbc.DriverDataSource$$anonfun$init$2.apply(DriverDataSource.scala:60)
at slick.jdbc.DriverDataSource$$anonfun$init$2.apply(DriverDataSource.scala:58)
at scala.Option.getOrElse(Option.scala:121)
Thanks to all for helping.
Vishal

Answer 1

I was running into the same connection issues when first using Slick. I submitted this PR with details on how to connect up a local Postgres server.
https://github.com/slick/slick/issues/1861#issuecomment-387616310.
But basically try edit your build.sbt and application.conf files:

Answer 2

The 2020 answer:
You have to make sure of two things:
Add the driver to the build.sbt's libraryDependencies: "org.postgresql" % "postgresql" % "42.2.5". That will cause java.sql.DriverManager's method getDrivers (which is used by slick in class DriverDataSource) to find the driver org.postgresql.Driver
Make sure that the database url in application.conf is following the JDBC's full-url pattern, as described in the source code: https://github.com/slick/slick/blob/42d787b4950fe876569b5fd68e98c4e0379ac83c/slick/src/main/scala/slick/jdbc/DatabaseUrlDataSource.scala#L9. For example: postgresql://user:password#localhost:5432/postgres.
My full configuration is:
build.sbt
libraryDependencies ++= Seq(
...,
"org.postgresql" % "postgresql" % "42.2.5"
)
application.conf
slick-postgres {
profile = "slick.jdbc.PostgresProfile$"
db {
dataSourceClass = "slick.jdbc.DatabaseUrlDataSource"
properties = {
driver = "org.postgresql.Driver"
url = "postgresql://postgres:postgres#localhost:5432/postgres"
}
}
}

Answer 3

I added the exception handling as suggested by sarvesh. That was cool and thank you. However my problem vanished and there was no exception. What happened? Earlier in the day, I had attempted to access the DB using the java JDBC way. i.e. just to check that there is nothing wrong with DB and DB access. In the process, I downloaded and added the postgresDriver in the classpath. Earlier that was not the case. Since the driver was now in the path, the code just worked. Since I was not printing the exception, i was not realizing the error. I then removed the driver jar AND i got the following error.
01:44:08.224 [mydb.db-1] DEBUG slick.jdbc.JdbcBackend.statement - Preparing statement: select "mib_id" from "mibpoint"
01:44:08.224 [mydb.db-1] DEBUG slick.jdbc.DriverDataSource - Driver org.postgresql.Driver not already registered; trying to load it
java.lang.ClassNotFoundException: org.postgresql.Driver
at java.lang.ClassLoader.findClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at slick.util.ClassLoaderUtil$$anon$1.loadClass(ClassLoaderUtil.scala:12)
at slick.jdbc.DriverDataSource$$anonfun$init$2.apply(DriverDataSource.scala:60)
at slick.jdbc.DriverDataSource$$anonfun$init$2.apply(DriverDataSource.scala:58)
at scala.Option.getOrElse(Option.scala:121)
Thanks to all for helping. Vishal

Answer 4

mydb {
dataSourceClass = "slick.jdbc.DatabaseUrlDataSource"
properties = {
driver = "slick.driver.PostgresDriver$"
url = "postgres://postgresql:postgresql#localhost:5432/mydb"
}
}
Or.. you can try something like,
mydb = {
dataSourceClass = "org.postgresql.ds.PGSimpleDataSource"
properties = {
url = "jdbc:postgresql://localhost:5432/mydb"
user = "postgres"
password = "postgres"
}
numThreads = 10
}

Answer 5

You need the Postgres Driver on the classpath:
Try adding "org.postgresql" % "postgresql" % "42.1.4" to your libraryDependencies.