I’m trying to create a Post request path using the Akka HTTP Server and the Scala programming language.
After I successfully make and receive the post request data, I would like to access the value of the country field inside the device parameter.
What is the best way to access this parameter?
I am using SprayJSON as the marshaller.
The current code gives the error Found: Option[Option[String]] Required: String.
Again, the request is processed successfully, I just can’t figure out how to access the value of the country field inside the device parameter.
The code is as below.
The case classes:
case class Geo(country: Option[String])
case class Device(id: String, geo: Option[Geo])
case class dataRequest(id: String, device: Option[Device])
The Post Request path:
Path(“submit”) {
Post {
Entity(as[dataRequest]) { data_request_params =>
data_request_params.device.map(dev => dev.geo.map(geo => {
val geoDevice = geo.country
}))
}
}
}
The request body:
{
“id”: “fghq1I123”,
“device”: {
“id”: “0004a672f”,
“geo”: {
“Country”: “AU”
}
}
}
It seems the problem you have, based on the question you asked in your previous post is not with akka neither akka-http. It's with the type system of scala.
First you need to understand how the Option class work, and at the same time what is the difference between map and flatMap.
map method has the signature Option[A].map[B](A => B): Option[B]. Which means, it will transform the value contained inside the Option (if the Option is of type Some, otherwhise it will not do anything) from A to B. For example:// this produces a `Option[Int]`
val optionInt: Option[Int] = Option(1)
// this produces a `Option[String]` because the return type of the function I'm passing as parameter is a `String`
val optionString: Option[String] = optionInt.map(int => int.toString)
// this produces a `Option[Option[Boolean]` because the return type of the function is an `Option[Int]`
// remember that the map method expect a function A => B and returns B
// in the following example B is of type of Option
val optionOptionBoolean: Option[Option[Boolean]] =
optionInt
.map(int =>
optionString
.map(string => int == string)
)
flatMap method has the signature Option[A].flatMap[B](A => Option[B]): Option[B]. As you can see, the function expected is an Option[B] and the return type is Option[B]. This is the one that does the magic you need for this specific case// a class with an Option field
case class NestedOption(optionInt: Option[Int])
// a class with a field that is an Option of another class that contains an Option field
case class Root(nestedOption: Option[NestedOption])
val nestedOption: Option[NestedOption] = Some(NestedOption(1))
val root: Root = Root(nestedOption)
// to access the nested Option field and transform from Option[Int] to Option[String]
val optionString = root
.flatMap( nestedOption => // I have access to the field `nestedOption` of Root
nestedOption
.optionInt // this field is of type Option, where I can call `map`
.map( int => i.toString) // returning an Option[String] for the `flatMap`
)
// this can also be written much cleaner using for yield
val optionString = for {
nestedOption <- root
int <- nestedOption.nestedOption.optionInt
} yield int.toString
To fix the error in your code
Path(“submit”) {
Post {
Entity(as[dataRequest]) { data_request_params =>
// the code below will return an Option of the value type you return in the last line
// if some of the `Option`s are None, you will get a `None`
val anotherOption = for {
device <- data_request_params.device
geo <- device.geo
country <- geo.country
} yield // the logic you need to apply here
}
}
}
Here you have a good link to learn more about Option
At the same time, I suggest to first learn the basics of Scala.