Postgres JDBC in scala unable to run two queries without restarting sbt - postgresql

Question

I am connecting to a postgres database with scala (2.9.2).
First time I make a SELECT (by running the code with 'run' in the sbt terminal in IntelliJ) it works well, but if I do 'run' again in the sbt shell I get an error that claims:
[error] (run-main) java.sql.SQLException: No suitable driver found for jdbc:postgresql://localhost/db
java.sql.SQLException: No suitable driver found for jdbc:postgresql://localhost/db
at java.sql.DriverManager.getConnection(DriverManager.java:602)
at java.sql.DriverManager.getConnection(DriverManager.java:185)
at SequenceGenerator$.connect(Validator.scala:50)
at SequenceGenerator$.generate(Validator.scala:54)
at Main$.main(Validator.scala:32)
at Main.main(Validator.scala)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
I have installed the postgres connector through sbt, this row in my build.sbt file.
libraryDependencies += "postgresql" % "postgresql" % "9.1-901.jdbc4"
This is my code for making a SELECT:
object SequenceGenerator{
def connect() = {
DriverManager.getConnection("jdbc:postgresql://localhost/db","user", "pass")
}
def generate() = {
val db = connect()
val st = db.createStatement
val res = st.executeQuery("SELECT value from table LIMIT 2")
while( res.next) {
println(res.getString("value"))
}
}
}

Answer 1

We had to add this to our integration tests startup to get around the same issue with the mysql jdbc driver:
Class.forName("com.mysql.jdbc.Driver").newInstance
I'm not sure why SBT unloads the driver, but something like this would probably work for you:
object SequenceGenerator{
//Use whatever your jdbc driver class should be here, I'm just guessing
Class.forName("org.postgresql.Driver").newInstance
def connect() = {
DriverManager.getConnection("jdbc:postgresql://localhost/db","user", "pass")
}
def generate() = {
val db = connect()
val st = db.createStatement
val res = st.executeQuery("SELECT value from table LIMIT 2")
while( res.next) {
println(res.getString("value"))
}
}
}

Answer 2

The main problem is that you are trying to load the driver using the old DriverManager approach. You have to use Database.forDataSource approach in slick and use a proper Database Pool like C3P0.
I think this is a classloading issue between Slick, SBT and the Driver.
Obviously make sure that the driver is in the classpath.