I got following errors after upgraded play framework from 2.5 to 2.6.
(It was able to compile with 2.5)
Scala version: 2.11.8
ambiguous reference to overloaded definition,
[error] both method emailAddress in trait Constraints of type => play.api.data.validation.Constraint[String]
[error] and method emailAddress in trait Constraints of type (errorMessage: String)play.api.data.validation.Constraint[String]
[error] match argument types (String)
[error] Constraints.emailAddress("test#sample.com")
^
Is there any way to use methods under Constraints with Play 2.6?
import play.api.data.validation._
val result = Constraints.emailAddress("test#sample.com")
emailAddress is a method which internally calls the another overridden method emailAddress(errorMessage: String = "error.email") method so if you call emailAddress with parameter that will give compilation error, so you can test it like this
val result = Constraints.emailAddress
result("test#sample.com")
Related
I was wondering why ScalaTest behaves differently compared to Specs2.
Specs2
"" must be equalTo 3
TestSpec.scala:11:26: type mismatch;
[error] found : Int(3)
[error] required: String
[error] "" must be equalTo 3
ScalaTest
3 should === ("r")
[info] Done compiling.
[info] TestTest:
[info] Dummy test
[info] - should fail *** FAILED ***
[info] "" did not equal 3 (PersistentTaskRuntimeTest.scala:21)
ScalaTest by default only fails at runtime, everything is compared as Any-to-Any.
There is the Supersafe plugin to get better checks (or TypeCheckedTripleEquals) but these feel like hacks as Specs2 just uses the scala compiler to require the types of the two values compared to be in a subtype/supertype relationship.
For reference this is the output when using TypeCheckedTripleEquals, mind the hacky CanEqual
TestTest.scala:21:7: types String and Int do not adhere to the type constraint selected for the === and !== operators; the missing implicit parameter is of type org.scalactic.CanEqual[String,Int]
[error] "" should === (3)
[error] ^
So what is the rationale behind this?
Less heavy for the scala compiler?
Less code to write for ScalaTest?
Less implicit magic (cryptic error messages)?
Pushing a commercial compiler plugin?
TypeCheckedTripleEquals is using generalised type constraints, for example, B <:< A in
implicit override def typeCheckedConstraint[A, B](implicit equivalenceOfA: Equivalence[A], ev: B <:< A): A CanEqual B
This is standard Scala functionality to enforce compile-time safety, and is used in many widespread Scala libraries. For example,
import org.scalactic.TypeCheckedTripleEquals
import org.scalatest._
class CompileTimeSafetySpec extends FlatSpec with Matchers with TypeCheckedTripleEquals {
"TypeCheckedTripleEquals" should "provide compile-time safety" in {
3 should === ("r")
}
}
gives compiler error
types Int and String do not adhere to the type constraint selected for the === and !== operators; the missing implicit parameter is of type org.scalactic.CanEqual[Int,String]
[error] 3 should === ("r")
I have been trying to create a Generic Dao over Slick 3.1.1 and it includes a generic filter that competes with JPA's findByExample, see the following files:
GenericDaoImpl.scala Generic level reusable across all Models
UserDao.scala Generic plus customizations for the User model
UserService.scala Wraps the UserDao into more services level functionality
In this last file I try to use the generic filter function to find a user by its registered email, like this:
// this will implicitly exec and wait indefinitely for the
// db.run Future to complete
import dao.ExecHelper._
def findByEmail(email: String): Option[UserRow] = {
userDao.filter(_.email === email).headOption
}
but this produces the compiler error:
[error] /home/bravegag/code/play-authenticate-usage-scala/app/services/UserService.scala:35: value === is not a member of String
[error] userDao.filter(email === _.email).headOption
[error] ^
[error] /home/bravegag/code/play-authenticate-usage-scala/app/services/UserService.scala:35: ambiguous implicit values:
[error] both value BooleanOptionColumnCanBeQueryCondition in object CanBeQueryCondition of type => slick.lifted.CanBeQueryCondition[slick.lifted.Rep[Option[Boolean]]]
[error] and value BooleanCanBeQueryCondition in object CanBeQueryCondition of type => slick.lifted.CanBeQueryCondition[Boolean]
[error] match expected type slick.lifted.CanBeQueryCondition[Nothing]
[error] userDao.filter(email === _.email).headOption
[error] ^
Can anyone advice on how the implicit declaration of the filter function below can be improved to solve this compiler error?
The implementation of the filter function (found in GenericDaoImpl.scala) is:
// T is defined above as T <: Table[E] with IdentifyableTable[PK]
override def filter[C <: Rep[_]](expr: T => C)
(implicit wt: CanBeQueryCondition[C]) : Future[Seq[E]] =
db.run(tableQuery.filter(expr).result)
As far as I can see you are simply lacking you profile API import in UserService.
Just add there this import: import profile.api._ and it should work.
EDIT: BTW I see many people building their own version of base CRUDs for Slick. Did you try some existing thin libraries doing just that e.g. here: https://github.com/VirtusLab/unicorn ? It's not really related to this question but it may be worth to take a look.
Right now trying to instantiate a new JSONConverter to register Jackson's Scala module.
private def getConverter(implicit m: ClassTag[T]) = {
new JSONConverter[T](classTag[T].runtimeClass, bucketName)
JSONConverter.registerJacksonModule(DefaultScalaModule)
converter
}
The above code sits in a standard Scala trait that looks like trait Writeable[T] { }.
The problem with the above code is that Scala seems to be having a difficult time with Types. Compiler error is:
[error] found : Class[_$1] where type _$1
[error] required: Class[T]
[error] val converter = new JSONConverter[T](classTag[T].runtimeClass, bucketName(clientId))
[error] ^
[error] one error found
Anyone know the source or easy fix of this issue? Thanks!
Update
Although #wingedsubmariner had an answer that allowed this to originally compile, as soon as I went to write more code the issue cascaded further. I'll show an example:
val o = bucketLookup(clientId).fetch(id, classTag[T].runtimeClass).withConverter(converter).withRetrier(DB.retrier).r(DB.N_READ).execute()
At withConverter the compiler throws the same error:
[error] found : com.basho.riak.client.convert.JSONConverter[T]
[error] required: com.basho.riak.client.convert.Converter[_$1] where type _$1
[error] val o = bucketLookup(clientId).fetch(id, classTag[T].runtimeClass).withConverter(converter).withRetrier(DB.retrier).r(DB.N_READ).execute()
I even tried doing the same type casting using converter.asInstanceOf[JSONConverter[T]] but inheritance (JSONConverter<T> extends Converter<T>) seems to cascade the issue. Any ideas here?
runtimeClass is retuning a Class with the wrong type parameter. Try:
new JSONConverter(classTag[T].runtimeClass.asInstanceOf[Class[T]], bucketName(clientId))
import scala.slick.driver.MySQLDriver.simple._
class RichTable[T](tag: Tag, name: String) extends Table[T](tag, name) {
case class QueryExt[B](q: Query[RichTable.this.type, B]) {
def whereEq[C](col: RichTable.this.type => Column[C], c: C) = {
q.filter { fields =>
col(fields) === c
}
}
}
}
Then it complains
[error] /home/jilen/workspace/play-slick/src/main/scala/play/slick/SlickQueryExtension.scala:10: value === is not a member of slick.driver.MySQLDriver.simple.Column[C]
[error] col(fields) === c
[error] ^
[error] /home/jilen/workspace/play-slick/src/main/scala/play/slick/SlickQueryExtension.scala:9: ambiguous implicit values:
[error] both value BooleanColumnCanBeQueryCondition in object CanBeQueryCondition of type => scala.slick.lifted.CanBeQueryCondition[scala.slick.lifted.Column[Boolean]]
[error] and value BooleanOptionColumnCanBeQueryCondition in object CanBeQueryCondition of type => scala.slick.lifted.CanBeQueryCondition[scala.slick.lifted.Column[Option[Boolean]]]
[error] match expected type scala.slick.lifted.CanBeQueryCondition[Nothing]
[error] q.filter { fields =>
[error] ^
[error] two errors found
[error] (compile:compile) Compilation failed
[error] Total time: 0 s, completed Mar 6, 2014 1:21:48 AM
There have been questions about this, but the answers did not work for 2.0
How to parametrize Scala Slick queries by WHERE clause conditions?
Slick doesn't have any information about C, so it doesn't know if it can and how it should map it to a database value and if it can use === on it. So you get a type error. You will have to use Scala's type system to restrict the type to one for which Slick knows how to map it. You can do this by providing a so-called Context Bound, in this case :BaseColumnType.
def whereEq[C:BaseColumnType](col: RichTable.this.type => Column[C], c: C) = {
q.filter { fields =>
col(fields) === c
}
}
BaseColumnType is provided by Slick and using it in this way basically tells the Scala compiler to look for an implicit value of type BaseColumnType[C] in scope, where you call whereEq. Because then it is usually known what C will actually be. Slick comes with BaseColumnType[Int], BaseColumnType[String], etc. so at the call site, the Scala compiler can find one when your C is really an Int or String in that particular call and this way pass the info further to Slick.
Same for LiuTiger's question. abstract class Crud[..., PK:BaseColumnType] should do the trick, a trait doesn't work with context bounds. When implementing an abstract DAO be prepared to face a lot of challenges and get to the edges of your Scala type system skills and learn quite a bit about type inference order, implicit parameters, etc.
I'm trying to use the sequenceU function on a List of Validation objects, but I keep on getting the error:
type mismatch;
found : G.M[List[G.A]]
required: scalaz.package.ValidationNEL[com.gaiam.gcsis.ws.validation.DataError,List[com.gaiam.gcsi.entities.plan.Service]]
[ERROR] val services: ValidationNEL[DataError, List[Service]] = valServices.sequenceU
I have two types here. The DataError class is a scala class (non-case class). The Service class is a Java class.
And here is the code where I receive this error.
val valServices: List[ValidationNEL[DataError, Service]] = XXX
val services: ValidationNEL[DataError, List[Service]] = valServices.sequenceU
Any thoughts on why I keep getting the type mismatch? I am on 7.0.0-M7.
You are probably on a 2.9.x version of Scala. Add -Ydependent-method-types as a compiler option