I have created a simple routes:
class MyRoutes[F[_] : Async](service: MyService[F]) extends Http4sDsl[F] {
def routes: HttpRoutes[F] = HttpRoutes.of[F] {
case req#PUT -> Root / "bets" =>
for {
bet <- req.as[Bet]
created <- service.put(bet)
response <- Created(created)
} yield response
}
and a jsons implicits for input and output:
object jsons {
implicit def circeDecoder[A[_] : Sync, B: Decoder]: EntityDecoder[A, B] = jsonOf[A, B]
implicit def circeEncoder[A[_] : Sync, B: Encoder]: EntityEncoder[A, B] = jsonEncoderOf[A, B]
}
But when I ran this program via Postman, I got an error:
The request body was invalid. with 422 error code. I think it is something wrong with json encoder and decoder, because my request was very simple and clear:
{
"stake": 434,
"name": "Something"
}
I tried to add an implicit decoder into routes:
implicit val betDecoder: EntityDecoder[F, Bet] = jsonOf[F, Bet]
but it also did not help. Could anyone help me with that and tell how to create good encoder and decoder for jsons? I use circe library for parsing.
Ok, stupid me, I solved the problem.
I had (probably) wrong definition of Bet. It was:
case class Bet(betId: BetId, stake: BigDecimal, name: String)
case class BetId(betId: String) extends AnyVal
So I should to give Id as a parameter. I changed the code to this one:
case class Bet(betId: Option[BetId], stake: BigDecimal, name: String)
case class BetId(betId: String) extends AnyVal
and after this one everything works correctly.
Another question is - is it good practise or could it be done in better way?
Related
My question concerns the second solution offered by mixel here: Scala Circe with generics
Note that the trait named Auto in Circe has been renamed to AutoDerivation in the current version of Circe.
I am using the solution mixel provides in his StackOverflow solution but have not been able to get it to work. I have tried things like updating my Circe version to the most recent one and making sure the Macro Paradise plugin is imported, but still no luck.
Here is my code. The first is its own file, called CirceGeneric.
import io.circe._
import io.circe.parser._
import io.circe.generic.extras._
object CirceGeneric {
trait JsonEncoder[T] {
def apply(in: T): Json
}
trait JsonDecoder[T] {
def apply(s: String): Either[Error, T]
}
object CirceEncoderProvider {
def apply[T: Encoder]: JsonEncoder[T] = new JsonEncoder[T] {
def apply(in: T) = Encoder[T].apply(in)
}
}
object CirceDecoderProvider {
def apply[T: Decoder]: JsonDecoder[T] = new JsonDecoder[T] {
def apply(s: String) = decode[T](s)
}
}
}
object Generic extends AutoDerivation {
import CirceGeneric._
implicit def encoder[T: Encoder]: JsonEncoder[T] = CirceEncoderProvider[T]
implicit def decoder[T: Decoder]: JsonDecoder[T] = CirceDecoderProvider[T]
}
The second is a method for unit testing that uses the Akka function responseAs. The method appears in a class called BaseServiceTest.
def responseTo[T]: T = {
def response(s: String)(implicit d: JsonDecoder[T]) = {
d.apply(responseAs[String]) match {
case Right(value) => value
case Left(error) => throw new IllegalArgumentException(error.fillInStackTrace)
}
}
response(responseAs[String])
}
The idea is to convert the result of responseAs[String] (which returns a string) into a decoded case class.
The code is not behaving as expected. Intellij does not detect any missing implicits, but when compilation time comes around, I am getting problems. I should mention that the BaseServiceTest file contains imports for CirceGeneric._ and Generic._, so a missing import statement is not the problem.
[error] [...]/BaseServiceTest.scala:59: could not find implicit value for parameter d: [...]CirceGeneric.JsonDecoder[T]
[error] response(responseAs[String])
Either the implicit conversion from Decoder[T] to JsonDecoder[T] is not happening, or the Decoder[T] instance is not being created. Either way, something is wrong.
You still need a Decoder or JsonDecoder context bound on responseTo.
def responseTo[T : Decoder]: T = ...
This is because all your code, and indeed mixel's code in the linked answer, is about abstracting from a Decoder out to a JsonDecoder trait which can be used for cross-library support. But you still don't have any way of constructing one without an underlying Decoder instance.
Now, there are some ways of automatically generating Decoders for (for instance) case classes contained in circe.generics.auto, but at this point in your code
def responseTo[T]: T = {
def response(s: String)(implicit d: JsonDecoder[T]) = ...
...
}
you're asking the compiler to be able to provide an implicit JsonDecoder (i.e., in your setup, Decoder) instance for any arbitrary type. As the accepted answer to the linked question explains, that's not possible.
You need to delay the implicit resolution to the point where you know what type you're dealing with - in particular, that you can provide a Decoder[T] instance for it.
EDIT: In your response to your comment regarding what the point is if you can't create JsonDecoders for all types...
My understanding of the linked question is that they're trying to abstract away the circe library in order to allow swapping out the JSON library implementation. This is done as follows:
add the JsonDecoder type class
have a package json which contains implicits (using Circe) for constructing them automatically via the package object extending AutoDerivation
have external code only refer to JsonDecoder and import the implicits in the json package
Then all the JSON serialization and implicit resolution works out without ever needing the calling code to reference io.circe, and it's easy to switch over the json/JsonDecoder to another JSON library if desired. But you're still going to have to use the JsonDecoder context bound, and be restricted to working with types where such an implicit can be constructed. Which is not every type.
As a beginner to both scala and akka-http, I am trying to hook into the serialization aka marshalling process.
The project uses akka#2.5.2 and akka-http#10.0.10". Furthermore, it has the akka-http-spray-json dependency included.
In the codebase, we use Java.Util.Currency (It may be deprecated which is not important as I'd still like to know how to add a custom marshaller.)
Given this example controller:
def getCurrencyExample: Route = {
path("currencyExample") {
val currency: Currency = Currency.getInstance("EUR")
val code: String = currency.getCurrencyCode
val shouldBeFormated = collection.immutable.HashMap(
"currencyCode" -> code,
"currencyObject" -> currency
)
complete(shouldBeFormated)
}
}
I get a response like this where the currency object becomes empty:
{
currencyObject: { },
currencyCode: "EUR",
}
I expect something like:
{
currencyObject: "EUR",
currencyCode: "EUR",
}
The currency object should be transformed into a JSON string. And since I do not want to transform each response manually, I want to hook into marshalling process and have it done in the background.
I want to add a custom marhaller only for Java.Util.Currency objects, yet even reading up on the docs I am very unsure how to proceed.
There are multiple approaches described, and I am not sure which fits my need, or where to start.
I tried creating my own CurrencyJsonProtocol:
package com.foo.api.marshallers
import java.util.Currency
import spray.json.{DefaultJsonProtocol, JsString, JsValue, RootJsonFormat}
object CurrencyJsonProtocol extends DefaultJsonProtocol {
implicit object CurrencyJsonFormat extends RootJsonFormat[Currency] {
override def read(json: JsValue): Currency = {
Currency.getInstance(json.toString)
}
override def write(obj: Currency): JsValue = {
JsString(obj.getCurrencyCode)
}
}
}
yet the mere existence of the file breaks my project:
[error] RouteDefinitons.scala:90:16: type mismatch;
[error] found : scala.collection.immutable.HashMap[String,java.io.Serializable]
[error] required: akka.http.scaladsl.marshalling.ToResponseMarshallable
[error] complete(shouldBeFormated)
[error] ^
[error] one error found
[error] (Compile / compileIncremental) Compilation failed
and I have no idea why. (It was crashing due to my package name being called marshaller. That completely broke the compilation of the project.
From what I understand, you have all the pieces, you just need to put them together.
Spray json provides support for marshalling common types, such as Int, String, Boolean, List, Map, etc. But it doesn't know how to marshall 'Currency'. And to solve that you have created a custom marshaller for 'Currency' objects. You just need to plug it in the right place. All that you have to do is import the marshaller from your CurrencyJsonProtocol into your Controller like below:
import CurrencyJsonProtocol._
Also make sure you have the below imports as well:
import spray.httpx.SprayJsonSupport._
import spray.json.DefaultJsonProtocol._
And spray-json should automatically pick that up.
To understand how it works, you need to understand about implicits in scala. Although it looks like magic when you come from java-world like me, I can assure you it's not.
I´m using Spray support for years. Maybe i should try another one. Anyway, in Spray, a custom formatter for a type is simple. An example of the squants.market.currency https://github.com/typelevel/squants
import squants.market.{ Currency, Money }
import squants.market._
trait MoneyJsonProtocol extends DefaultJsonProtocol {
implicit object CurJsonFormat extends JsonFormat[Currency] {
def write(currency: Currency): JsValue = JsString(currency.code)
def read(value: JsValue): Currency = value match {
case JsString(currency) =>
defaultCurrencyMap.get(currency) match {
case Some(c) => c
case None => // throw an exception, for example
}
case _ => // throw another exception, for example
}
}
implicit def toJavaBigDecimal(b: math.BigDecimal): java.math.BigDecimal = b.underlying
}
Do you have a JsonFormat[Currency]? If yes, just fix it...
If not, you should follow the doc and create:
as domain model, specific result type to hold the answer e.g. case class CurrencyResult(currency: Currency, code: String)
in trait JsonSupport: a JsonFormat[Currency]
in trait JsonSupport: a JsonFormat[CurrencyResult]
As an alternative to point 1 above, you can probably type your map as: Map[String, JsValue].
I would like to design a base trait/class in Scala that can produce the following json:
trait GenericResource {
val singularName: String
val pluralName: String
}
I would inherit this trait in a case class:
case class Product(name: String) extends GenericResource {
override val singularName = "product"
override val pluralName = "products"
}
val car = Product("car")
val jsonString = serialize(car)
the output should look like: {"product":{"name":"car"}}
A Seq[Product] should produce {"products":[{"name":"car"},{"name":"truck"}]} etc...
I'm struggling with the proper abstractions to accomplish this. I am open to solutions using any JSON library (available in Scala).
Here's about the simplest way I can think of to do the singular part generically with circe:
import io.circe.{ Decoder, Encoder, Json }
import io.circe.generic.encoding.DerivedObjectEncoder
trait GenericResource {
val singularName: String
val pluralName: String
}
object GenericResource {
implicit def encodeResource[A <: GenericResource](implicit
derived: DerivedObjectEncoder[A]
): Encoder[A] = Encoder.instance { a =>
Json.obj(a.singularName -> derived(a))
}
}
And then if you have some case class extending GenericResource like this:
case class Product(name: String) extends GenericResource {
val singularName = "product"
val pluralName = "products"
}
You can do this (assuming all the members of the case class are encodeable):
scala> import io.circe.syntax._
import io.circe.syntax._
scala> Product("car").asJson.noSpaces
res0: String = {"product":{"name":"car"}}
No boilerplate, no extra imports, etc.
The Seq case is a little trickier, since circe automatically provides a Seq[A] encoder for any A that has an Encoder, but it doesn't do what you want—it just encodes the items and sticks them in a JSON array. You can write something like this:
implicit def encodeResources[A <: GenericResource](implicit
derived: DerivedObjectEncoder[A]
): Encoder[Seq[A]] = Encoder.instance {
case values # (head +: _) =>
Json.obj(head.pluralName -> Encoder.encodeList(derived)(values.toList))
case Nil => Json.obj()
}
And use it like this:
scala> Seq(Product("car"), Product("truck")).asJson.noSpaces
res1: String = {"products":[{"name":"car"},{"name":"truck"}]}
But you can't just stick it in the companion object and expect everything to work—you have to put it somewhere and import it when you need it (otherwise it has the same priority as the default Seq[A] instances).
Another issue with this encodeResources implementation is that it just returns an empty object if the Seq is empty:
scala> Seq.empty[Product].asJson.noSpaces
res2: String = {}
This is because the plural name is attached to the resource at the instance level, and if you don't have an instance there's no way to get it (short of reflection). You could of course conjure up a fake instance by passing nulls to the constructor or whatever, but that seems out of the scope of this question.
This issue (the resource names being attached to instances) is also going to be trouble if you need to decode this JSON you've encoded. If that is the case, I'd suggest considering a slightly different approach where you have something like a GenericResourceCompanion trait that you mix into the companion object for the specific resource type, and to indicate the names there. If that's not an option, you're probably stuck with reflection or fake instances, or both (but again, probably not in scope for this question).
For example suppose I have
case class Test(a: String, b: String)
...
implicit val testFormat = jsonFormat2(Test.apply)
and a json with an extra c field:
val test = "{\"a\": \"A\", \"b\": \"B\", \"c\": \"C\"}"
then I want to find a way (config/param/whatever) to make the following line throw and exception:
test.parseJson.convertTo[Test]
It's very hard to work this out from reading the source code and github documentation.
I didn't see anything in the library that provides that functionality, so I created a wrapper that does a quick check on the number of fields present before delegating the read call to the supplied formatter.
case class StrictRootFormat[T](format: RootJsonFormat[T], size: Int) extends RootJsonFormat[T] {
def read(json: JsValue): T = {
if(json.asJsObject.fields.size > size) deserializationError("JSON has too many fields: \n " + json.toString())
else format.read(json)
}
def write(obj: T): JsValue = format.write(obj)
}
Usage:
implicit val testFormat = StrictRootFormat(jsonFormat2(Test.apply), 2)
You could enhance the read implementation so that you don't need to supply the "size" argument.
[edit]
So, i got a quick and dirty solution, thanks to Edmondo1984, I don't know if it's the best solution. I don't handle null values with pattern matching at the write function. You can read more details about my problem after this editing. Here is my code now:
object DBNames extends DefaultJsonProtocol {
implicit val pkFormat: JsonFormat[Pk[Int]] = new JsonFormat[Pk[Int]] {
def write(obj: Pk[Int]): JsValue = JsNumber(obj.get)
def read(json: JsValue): Pk[Int] = json.asJsObject.getFields("id") match {
case Seq(JsNumber(id)) => new Pk[Int] { id.toInt }
case _ => throw new DeserializationException("Int expected")
}
}
implicit val nameFormat = jsonFormat2(Name)
jsonFormat2 will implicitly use pkFormat to parse Pk[Int] values.
In my controller class I have this:
def listNames() = Action {
val names = DBNames.findAll()
implicit val writer = DBNames.nameFormat
var json = names.toJson
Ok(json.toString()).as("application/json")
}
I had to get the nameFormat from my model and make it implicit, so bars.toJson could use it to parse the Seq[Name] names.
[/edit]
I'm trying to use Play! Framework with Scala, I'm new to Scala programming and Play Framework, and everything seems nice, but I'm working on this problem during several hours and didn't find a solution.
I have a Case Class:
case class Name (id: Pk[Int], name: String)
And an object to deal with MySql. I created a implicit val nameFormat = jsonFormat2(Name) to deal with JSON.
object DBNames extends DefaultJsonProtocol {
implicit val nameFormat = jsonFormat2(Name)
var parser =
{
get[Pk[Int]]("id") ~
get[String]("name") map {
case id ~ name => Name(id,name)
}
}
def findAll():Seq[Name] =
{
DB.withConnection {
implicit connection =>
SQL("select * from names").as(DBNames.parser *)
}
}
def create(name: Name){
DB.withConnection {
implicit connection =>
SQL("insert into names (name) values ({name})").on(
'name -> name.name
).executeUpdate()
}
}
}
But when I try to compile it, Play! gives me this result:
[error] D:\ProjetosJVM\TaskList\app\models\Names.scala:20: could not find implicit value for evidence parameter of type models.DBNames.JF[anorm.Pk[Int]]
It seems like he couldn't find a way to parse the id value, since it is a Pk[Int] value.
So, by reading this: https://github.com/spray/spray-json I didn't found a way to parse it without creating a complete object parser like they show in the documentation:
object MyJsonProtocol extends DefaultJsonProtocol {
implicit object ColorJsonFormat extends RootJsonFormat[Color] {
def write(c: Color) = JsObject(
"name" -> JsString(c.name),
"red" -> JsNumber(c.red),
"green" -> JsNumber(c.green),
"blue" -> JsNumber(c.blue)
)
def read(value: JsValue) = {
value.asJsObject.getFields("name", "red", "green", "blue") match {
case Seq(JsString(name), JsNumber(red), JsNumber(green), JsNumber(blue)) =>
new Color(name, red.toInt, green.toInt, blue.toInt)
case _ => throw new DeserializationException("Color expected")
}
}
}
}
I have a "big" (actually small) project where I want to make most of things work with Ajax, so I think this is not a good way to do it.
How can I deal with JSON objects in this project, where almost all case classes will have a "JSON parser", without creating large ammounts of code, like the snippet above? And also, how can I make it work with an Seq[Name]?
You don't need to write a complete parser. The compiler says:
[error] D:\ProjetosJVM\TaskList\app\models\Names.scala:20: could not find implicit
value for evidence parameter of type models.DBNames.JF[anorm.Pk[Int]]
The scala compiler is looking for an implicit parameter of type JF[anorm.Pk[Int]] and there is no such an implicit parameter in scope. What is JF[anorm.Pk[Int]]? Well, you need to know the library and I didn't, so I had browsed spray-json source and found out:
trait StandardFormats {
this: AdditionalFormats =>
private[json] type JF[T] = JsonFormat[T] // simple alias for reduced verbosity
so JF[T] is just an alias for JsonFormat[T]. It all make sense: PK[Int] is a class coming from Anorm and spray-json provides out-of-the-box json support for standard types, but does not even know Anorm exists So you have to code your support for Pk[Int] and make it implicit in scope.
You will have code like the following:
object DBNames extends DefaultJsonProtocol {
implicit val pkFormat : JsonFormat[Pk[Int]] = new JsonFormat[Pk[Int]] {
//implementation
}
// rest of your code
}
If you have just started with Scala, you would probably have to read more about implicits and their resolution. I am providing you with a minimal answer: once you have provided the right implementation, your code will compile. I suggest you to refer to the javadoc of anorm.Pk and of JsonFormat to understand how to implement it correctly for your type.
Pk looks like scala.Option and in StandardFormats source code inside spray-json you find the JsonFormat implementation for Option, from which you can copy