I want to send slick table as part of the akka actor message . So that the remote actor at the other end can connect to the database and can do CRUD operations on the mysql database. Am unable to get my head over the slick types and i find compiler/eclipse complaining. How can i get this done. Is it a good idea to pass slick queries as part of actor messages.
object RemoteActorMessages {
case class Create(table: Table[A])
case class RunQuery(query: Query[_, _, _])
case Result(code: Int, message: String)
}
class DBActor extends Actor {
def recieve = {
case Create(table) => createTable(table)
case RunQuery(query) => runQuery(query)
case ... //so on
}
}
def createTable(table: Table[M]): Future[A] = Future {
db.withSession(implicit session => tableQuery[table].ddl.create)
}
def runQuery(query: Query[_, _, _]): Future[A] = Future {
db.withSession { implicit session => {
query.run
}
}
}
warning: code might have some type errors.Discretion is appreciated from the viewers
I am confused about how to send results back to the sender of the messages. for example: query.list.run gives back list of model objects. So, how should i frame by Result message
I think this is a case of 'when you have a hammer everything becomes nails'. I believe this is not the right use case for the actors. A reason (not the only one) would be that DB operations are 'slow' and they would block the actor threads for a long time.
Arguably you want a service that manages the table operations, using Futures and a custom Execution Context to isolate the impact (for example, in Play is done like this). Something like:
object DBService {
def createTable() : Future[Boolean] = ???
...
}
Actors should only receive commands like CreateTable that then call the corresponding method in the service.
Incidentally, this would simplify your use case as the service could know more about the table and other Slick specifics, whilst the actor would be oblivious to them.
Not the only way, but arguably simpler.
Related
Consider following snippet; I have used WSClient here for some api calls via DI.
#Singleton
class SampleService #Inject()(ws: WSClient) {
def get(id:Long): JsValue ={
val trailingURL = s"/$id".toString
val wsRequest = ws.url(baseURL+trailingURL).addQueryStringParameters("access_token" -> authToken).get()
val wsResponse = Await.result(wsRequest, Duration.Inf)
Json.toJson(wsResponse.body)
}
}
And I need to write unit test for get method. I'm doing the following thing
val mockedWS = mock[WSClient]
val sparrowService = new SurveySparrowService(mockedWS)
"get method" should {
"return a valid result with valid id" in {
val result = sparrowService.get(66405)
println(result)
assert(result.toString == `the result i'll get`)
}
}
But the mocking fails and i get a null pointer exception in following line=>
val wsRequest = ws.url(baseURL+trailingURL).addQueryStringParameters("access_token" -> authToken).get()
Also when i'm using Json.toJson(wsResponse.body) i'm getting extra \ with each parameter in whole response.
can anyone help me solving these two problems. Thanks.
There is play-mockws, which exists solely because mocking a WSClient manually is really tedious.
// simulation of a GET request to http://dns/url
val ws = MockWS {
case (GET, "http://dns/url") => Action { Ok("http response") }
}
await(ws.url("http://dns/url").get()).body == "http response"
Further explanation:
Mocking a class / trait simply creates you an instance of that type out of thin air. You cannot do anything with that instance in general, calling any method on it will simply return null. If your code under test calls methods of this object, you must stub those methods with answers (i.e. simply return a prepared value).
For WSClient, this means you must stub the url method since this will be called by any code doing HTTP requests. But this method returns a WSRequest. So, you must mock this also... Any call on this new mock needs to be stubbed too, or else it will end in a NPE again. This really gets complicated very soon, and you probably don't understand your test code too well anymore. That's why play-mockws was created which makes it very easy to reason about calls to HTTP services in your Play application.
BTW, you may also combine play-mockws with the SIRD - String Interpolation Router DSL, which makes it even easier to extract values out of the routes or query parameters if you need to:
val ws = MockWS {
case GET(p"/$id") if id == "66405" =>
Action {
Results.Ok("...")
}
}
I'm working on a scala object in order to perform some testing
My start object is as follows
object obj1 {
def readvalue : IO[Float] = IO{
scala.io.StdIn.readFloat()
}
}
The testing should be
1- value of type FLOAT
2- should be less than 3
As we can not mock singleton objects I've used mocking functions here is what I've done.
class FileUtilitiesSpec
extends FlatSpec
with Matchers
with MockFactory
{
"value" should "be of Type Float" in {
val alpha = mockFunction[() => IO[Float]]
alpha.expects shouldBe a[IO[Float]]
}
"it" should "be less than 3" in {
val alpha = mockFunction[() => IO[Float]]
alpha.expects shouldBe <(3)
}
}
Im getting an error saying that :
MockFunction0-1() once (never called - UNSATISFIED) was not an instance of cats.effect.IO, but an instance of org.scalamock.handlers.CallHandler0
ScalaTestFailureLocation: util.FileUtilitiesSpec at (FileUtilitiesSpec.scala:16)
Expected :cats.effect.IO
Actual :org.scalamock.handlers.CallHandler0 ```
I would recommend reading the examples here as a starting point: https://scalamock.org/quick-start/
Using mock objects only makes sense if you are planning to use them in some other code, e.g. dependencies you do not want to make part of your module under test, or are beyond your control.
An example might be a database connection where you would depend on an actual system, making the code hard to test without simulating it.
The example you provided only has mocks, but no code using it, hence the error you are getting is absolutely correct. The mock expects to be used, but was not called.
The desired behaviour for a mocking library in this case is to make the test fail as the developer intended for this interaction with a mock to happen, but it was not recorded - so something is wrong.
No instance of play.api.libs.json.Format is available for models.AccountStatus in the implicit scope.
This is the code taken from a github page, and only class names and variable names are changed.
package models
import slick.jdbc.H2Profile._
import play.api.libs.json._
case class Account(id: Long, name: String, category: Int, status:AccountStatus)
object Account {
implicit val accountFormat = Json.format[Account]
}
sealed abstract class AccountStatus(val as:Int)
object AccountStatus{
final case object Draft extends AccountStatus(0)
final case object Active extends AccountStatus(1)
final case object Blocked extends AccountStatus(2)
final case object Defaulter extends AccountStatus(3)
implicit val columnType: BaseColumnType[AccountStatus] = MappedColumnType.base[AccountStatus,Int](AccountStatus.toInt, AccountStatus.fromInt)
private def toInt(as:AccountStatus):Int = as match {
case Draft => 0
case Active => 1
case Blocked => 2
case Defaulter => 3
}
private def fromInt(as: Int): AccountStatus = as match {
case 0 => Draft
case 1 => Active
case 2 => Blocked
case 3 => Defaulter
_ => sys.error("Out of bound AccountStatus Value.")
}
}
https://github.com/playframework/play-scala-slick-example/blob/2.6.x/app/models/Person.scala
So, this code needs to be added inside of the object AccountStatus code block since we need to use fromInt to transform an Int to an AccountStatus. This is a Reads defined for AccountStatus:
implicit object AccountStatusReads extends Reads[AccountStatus] {
def reads(jsValue: JsValue): JsResult[AccountStatus] = {
(jsValue \ "as").validate[Int].map(fromInt)
}
}
What's a Reads? It's just a trait that defines how a JsValue (the play class encapsulating JSON values) should be deserialized from JSON to some type. The trait only requires one method to be implemented, a reads method which takes in some json and returns a JsResult of some type. So you can see in the above code that we have a Reads that will look for a field in JSON called as and try to read it as an integer. From there, it will then transform it into an AccountStatus using the already defined fromInt method. So for example in the scala console you could do this:
import play.api.libs.json._
// import wherever account status is and the above reader
scala> Json.parse("""{"as":1}""").as[AccountStatus]
res0: AccountStatus = Active
This reader isn't perfect though, mainly because it's not handling the error your code will give you on out of bound numbers:
scala> Json.parse("""{"as":20}""").as[AccountStatus]
java.lang.RuntimeException: Out of bound AccountStatus Value.
at scala.sys.package$.error(package.scala:27)
at AccountStatus$.fromInt(<console>:42)
at AccountStatusReads$$anonfun$reads$1.apply(<console>:27)
at AccountStatusReads$$anonfun$reads$1.apply(<console>:27)
at play.api.libs.json.JsResult$class.map(JsResult.scala:81)
at play.api.libs.json.JsSuccess.map(JsResult.scala:9)
at AccountStatusReads$.reads(<console>:27)
at play.api.libs.json.JsValue$class.as(JsValue.scala:65)
at play.api.libs.json.JsObject.as(JsValue.scala:166)
... 42 elided
You could handle this by making the Reads handle the error. I can show you how if you want, but first the other part of a Format is a Writes. This trait, unsurprisingly is similar to reads except it does the reverse. You're taking your class AccountStatus and creating a JsValue (JSON). So, you just have to implement the writes method.
implicit object AccountStatusWrites extends Writes[AccountStatus] {
def writes(as: AccountStatus): JsValue = {
JsObject(Seq("as" -> JsNumber(as.as)))
}
}
Then this can be used to serialize that class to JSON like so:
scala> Json.toJson(Draft)
res4: play.api.libs.json.JsValue = {"as":0}
Now, this is actually enough to get your error to go away. Why? Because Json.format[Account] is doing all the work we just did for you! But for Account. It can do this because it's a case class and has less than 22 fields. Also every field for Account has a way to be converted to and from JSON (via a Reads and Writes). Your error message was showing that Account could not have a format automatically created for it because part of it (status field) had no formatter.
Now, why do you have to do this? Because AccountStatus is not a case class, so you can't call Json.format[AccountStatus] on it. And because the subclasses of it are each objects, which have no unapply method defined for them since they're not case classes. So you have to explain to the library how to serialize and deserialize.
Since you said you're new to scala, I imagine that the concept of an implicit is still somewhat foreign. I recommend you play around with it / do some reading to get a grasp of what to do when you see that the compiler is complaining about not being able to find an implicit it needs.
Bonus round
So, you might really not want to do that work yourself, and there is a way to avoid having to do it so you can do Json.format[AccountStatus]. You see Json.format uses the apply and unapply methods to do its dirty work. In scala, these two methods are defined automatically for case classes. But there's no reason you can't define them yourself and get everything they give you for free!
So, what do apply and unapply look like type signature wise? It changes per class, but in this case apply should match Int => AccountStatus (a function that goes from an int to an AccountStatus). So it's defined like so:
def apply(i: Int): AccountStatus = fromInt(i)
and unapply is similar to the reverse of this, but it needs to return an Option[Int], so it looks like
def unapply(as: AccountStatus): Option[Int] = Option(as.as)
with both of these defined you don't need to define the reads and writes yourself and instead can just call
// this is still inside the AccountStatus object { ... }
implicit val asFormat = Json.format[AccountStatus]
and it will work in a similar fashion.
.P.S. I'm traveling today, but feel free to leave any comments if some of this doesn't make sense and I'll try to get back to you later on
I'm trying to learn Scala and the Play Framework at the same time. Scala looks to me like it has a lot of really cool ideas, but one of my frustrations is trying to understand all of the different syntaxes for methods/functions/lambdas/anonymous functions/etc.
So I have my main application controller like so:
object Application extends Controller {
def index = Action {
Ok(views.html.index("Your new application is ready."))
}
}
This tells me I have a singleton Application that has one method, index, that returns what type?? I was expecting index to have a definition more like:
def index(req: Request) : Result = { ... }
Looking at Play Framework's documentation, it looks as though Action is a trait, that transforms a request to a result, by I'm having a hard time understanding what this line is saying:
def index = Action { ... }
I come from a Java background, so I don't know what this is saying? (this statement feels like it's saying "method index = [some interface Action]", which doesn't make sense to me; it seems something beautiful is happening, but it is magic to me, and I feel uneasy with magic in my code ;))
When you invoke an object as if it were a function, that's translated into a call to apply. I.e.:
foo(bar)
is translated into
foo.apply(bar)
So, inside index you are calling the Action object as if it were a function, which means you are actually calling Action.apply.
The return type of index is omitted because the compiler can infer it to be the return type of Action.apply (which I guess from the name is Unit).
So the short answer to this question is that there's some stuff going on behind the scenes that makes the above work: namely that the compiler is inferring types, and in Scala, objects with an apply method can get called as if they were functions.
So what's going on here is that this code:
def index = Action {
Ok("Hello World!")
}
...is equivalent to (or rather shorthand for) this code:
def index : Action[AnyContent] = Action.apply(
(req: Request[AnyContent]) => {
Ok(views.html.index("Hello World!"))
} : Result
)
The magic is happening here: ... = Action {...}. Action {...} says "call Action with this anonymous function {...}".
Because Action.apply is defined as apply(block: => Result): Action[AnyContent], all of the argument-/return- types can be inferred.
I would like to create a smart recursion prevention mechanism. I would like to be able to annotate a piece of code somehow, to mark that it should not be executed in recursion, and if it is indeed executed in recursion, then I want to throw a custom error (which can be caught to allow executing custom code when this happens)
Here is my attempt until here:
import scala.collection.mutable.{Set => MutableSet, HashSet => MutableHashSet }
case class RecursionException(uniqueID:Any) extends Exception("Double recursion on " + uniqueID)
object Locking {
var locks:MutableSet[Any] = new MutableHashSet[Any]
def acquireLock (uniqueID:Any) : Unit = {
if (! (locks add uniqueID))
throw new RecursionException(uniqueID)
}
def releaseLock (uniqueID:Any) : Unit = {
locks remove uniqueID
}
def lock1 (uniqueID:Any, f:() => Unit) : Unit = {
acquireLock (uniqueID)
try {
f()
} finally {
releaseLock (uniqueID)
}
}
def lock2[T] (uniqueID:Any, f:() => T) : T = {
acquireLock (uniqueID)
try {
return f()
} finally {
releaseLock (uniqueID)
}
}
}
and now to lock a code segment I do:
import Locking._
lock1 ("someID", () => {
// Custom code here
})
My questions are:
Is there any obvious way to get rid of the need for hard coding a unique identifier? I need a unique identifier which will actually be shared between all invocations of the function containing the locked section (so I can't have something like a counter for generating unique values, unless somehow scala has static function variables). I thought on somehow
Is there any way to prettify the syntax of the anonymouse function? Specifically, something that will make my code look like lock1 ("id") { /* code goes here */ } or any other prettier look.
A bit silly to ask in this stage, but I'll ask anyway - Am I re-inventing the wheel? (i.e. does something like this exist?)
Wild final thought: I know that abusing the synchronized keyword (at least in java) can gaurantee that there would be only one execution of the code (in the sense that no multiple threads can enter that part of the code at the same time). I don't think it prevents from the same thread to execute the code twice (although I may be wrong here). Anyway, if it does prevent it, I still don't want it (even thoug my program is single threaded) since I'm pretty sure it will lead to a deadlock and won't report an exception.
Edit: Just to make it clearer, this project is for error debugging purposes and for learning scala. It has no real useage other than easily finding code errors at runtime (for detecting recursion where it shouldn't happen). See the comments to this post.
Not quite sure what you're aiming at, but a few remarks:
First, you do not need to do lock1 and lock2 to distinguish Unit and the other type. Unit is a proper value type, the generic method will work for it too. Also, you should probably use a call by name argument => T, rather than a function () => T, and use two argument lists:
def lock[T] (uniqueID:Any)(f: => T) : T = {
acquireLock (uniqueID)
try {
f
} finally {
releaseLock (uniqueID)
}
}
Then you can call with lock(id){block} and it looks like common instructions such as if or synchronized.
Second, why do you need a uniqueId, why make Lock a singleton? Instead, make Lock a class, an have as many instances as you would have had ids.
class Lock {
def lock[T](f: => T): T = {acquireLock() ...}
}
(You may even name your lock method apply, so you can just do myLock{....} rather than myLock.lock{...})
Multithreading aside, you now just need a Boolean var for acquire/releaseLock
Finally, if you need to support multithreading, you have to decide whether several thread can enter the lock (that would not be recursion). If they can, the boolean should be replaced with a DynamicVariable[Boolean] (or maybe a java ThreadLocal, as DynamicVariable is an InheritableThreadLocal, which you may or may not want). If they cannot, you just need to synchronize access in acquire/releaseLock.
Is there any obvious way to get rid of the need for hard coding a unique identifier?
Since for what you said on the comments this is not prod code, I guess you could use the functions hashCode property like this:
def lock1 (f:() => Unit) : Unit = {
acquireLock (f.hashCode)
try {
f()
} finally {
releaseLock (f.hashCode)
}
Is there any way to prettify the syntax of the anonymouse function?
With the before-mentioned change the syntax should be prettier:
lock1 {
If you're planning on keeping the identifier (if hashcode doesn't cut it for you) you can define your method like this:
def lock1 (uniqueID:Any)(f:() => Unit) : Unit = {
That will let you call the lock1 method with:
lock("foo") {
}
Cheers!